# Patent

## Title
Method and system for solubilizing protein

## Abstract

A process for solubilization of protein including application of an alkali, such as lime, and heating. The process may also involve lime recovery and may be accomplished in a single stage or two stages to separate protein solubilized from labile and recalcitrant sources. Systems and devices for use in such process, including a continuous stirred tank reactor and a plug flow reactor are also involved.

## Background
PRIORITY CLAIM
The present application is a Continuation-in-Part under 35 U.S.C. §120 of U.S. patent applications Ser. No. 10/703,985, titled “Process for Solubilizing Protein”, filed Nov. 7, 2003 and published as US 2004/0152881 on Aug. 5, 2004, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/424,668, titled “Process for Solubilizing Protein” filed Nov. 7, 2002. The present application also claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 60/576,180, titled “Method and System for Solubilizing Protein”, filed Jun. 1, 2004.


JOINT RESEARCH AGREEMENT
The inventions described herein were made pursuant to a Joint Research Agreement as set forth in 35 U.S.C. §103 (c)(3). The parties to the Joint Research Agreement are Terrabon, Inc. and Texas Engineering Experiment Station, a component of the Texas A&M University System.
FIELD OF THE INVENTION
The present invention relates to a process for solubilizing protein, particularly protein from sources in which protein is not readily solubilized. Some embodiments provide a process for destroying prions in solubilized protein.
BACKGROUND OF THE INVENTION
The growing world population has increased food requirements drastically during the past decades, leading to a bigger demand for protein sources for domesticated animals. The increased population also generates an increasing amount of waste that can be a valuable source for producing animal feed.
Processes for protein solubilization from biological sources are useful in turning protein in waste into valuable protein sources. Accordingly, a number of such process have been previously developed. Some processes function only with easily solubilized proteins. Others have been designed to improve solubilization of protein from sources where protein is not easily solubilized, such as chicken feathers.
Thermo-chemical treatments promote the hydrolysis of protein-rich materials, splitting complex polymers into smaller molecules, improving their digestibility, and generating products that enable animals to meet their needs for maintenance, growth, and production with less total feed.
One previous process for the solubilization of protein in chicken feathers involves steam treatment. In this process feathers are treated with steam to make feather meal. The process increases the solubility or digestibility of protein in the feathers only slightly.
Another previous process involves acid treatment of protein sources. The treatment hydrolyzes amino acids, but conditions are usually so harsh that many amino acids are destroyed. Also the acid conditions encourage the formation of disulfide bonds rather than the destruction of such bonds, which would aid solubility.
Additionally, conditions in previous systems may not be suitable for the destruction of prions in the original protein source.
SUMMARY OF THE INVENTION
The present invention includes a novel process for the solubilization of proteins. The process generally involves supplying an alkali, such as lime, to a biological source to produce a slurry. Protein in the slurry is hydrolyzed to produce a liquid product. The slurry may be heated to assist in hydrolysis. A solid residue may also result. This residue may be subjected to further processes of the present invention.
Some embodiments may also be used to separate high-quality protein for use in monogastric feed from low-quality protein which may be used in ruminant feed.
When some processes are used with plant protein sources, removal of the protein provides the additional benefit of simultaneously increasing the enzymatic digestibility of the plant fiber remaining in the solid residue.
According to one specific embodiment, the invention includes a method of solubilizing protein. The method may include applying an alkali to a protein source to form a slurry; heating the slurry to a temperature sufficient to allow hydrolysis of protein in the protein source to obtain a reaction liquid; separating solids from the reaction liquid; neutralizing the reaction liquid with acid or an acid source to produce a neutralized liquid; concentrating the neutralized liquid to produce concentrated liquid and water; and returning the water to the slurry before or during the heating step.
According to another specific embodiment, the invention includes a system for solubilizing protein. The system may include a heated reactor able to react a protein source and an alkali to produce a reaction liquid. It may also include a solid/liquid separator able to separate solids from the reaction liquid. The system may also have a neutralization tank able to allow addition of acid to the reaction liquid to produce a neutralized liquid and a concentration tank able to concentrate neutralized liquid and to produce a concentrated liquid and water. The system may further include a conduit able to pass water from the concentration tank to the heated reactor and at least one heat exchanger able to exchange process heat.
Additional advantages of some embodiments of the invention include:
Mixtures of labile and recalcitrant proteins may be processed simultaneously.
Presently existing plug flow reactors may be used.
Waste reduction is coupled with food or protein supplement production.
Protein digestibility increases significantly when it is solubilized.
The process is simple and allows recovery of some components and heat.
Food safety is improved if prions are destroyed.
Grinding increases the reaction rate of protein digestion, allowing for increased product concentration and decreased product degradation.
Nonreactive components may be purged.
The protein product may be concentrated and dried.
Microorganisms may be destroyed.
The invention also includes reactor systems suitable to house processes of the present invention.
For a better understanding of the invention and its advantages, reference may be made to the following description of exemplary embodiments and accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The following figures relate to selected embodiments of the present invention.
FIG. 1 shows a step-wise diagram for the hydrolysis of protein-rich material under alkaline conditions.
FIG. 2 is a graph showing the hydrolysis of chicken feathers and animal hair. Each point represents the average of three values +/−2 standard deviations.
FIG. 3 is a graph showing the reaction rate vs. conversion for animal hair and chicken feathers.
FIG. 4 is a graph showing conversion vs. time for protein hydrolysis of shrimp heads and chicken offal.
FIG. 5 is a graph showing conversion vs. time for protein hydrolysis of soybean hay and alfalfa hay.
FIG. 6 illustrates a single-stage solubilization process with no calcium recovery according to an embodiment of the present invention.
FIG. 7 illustrates a two-stage solubilization process with no calcium recovery according to an embodiment of the present invention.
FIG. 8 illustrates a one-stage solubilization process with calcium recovery according to an embodiment of the present invention.
FIG. 9 illustrates a two-stage solubilization process with calcium recovery according to an embodiment of the present invention.
FIG. 10 illustrates a one-stage reactor according to an embodiment of the present invention.
FIG. 11 illustrates a multi-stage reactor with countercurrent flow according to an embodiment of the present invention.
FIG. 12 illustrates a multi-stage reactor with cocurrent flow according to an embodiment of the present invention.
FIG. 13 illustrates a multi-stage reactor with crosscurrent flow according to an embodiment of the present invention.
FIG. 14 illustrates a plug flow reactor with a unitized mixer and exit screw conveyor according to an embodiment of the present invention.
FIG. 15 illustrates a plug flow reactor with a separated mixer and exit screw conveyor according to an embodiment of the present invention.
FIG. 16 illustrates a plug flow reactor with a lock hopper according to an embodiment of the present invention.
FIG. 17 illustrates an experimental setup for protein hydrolysis studies.
FIG. 18 is a graph illustrating the temperature effect on protein solubilization of alfalfa hay.
FIG. 19 is a graph illustrating the lime loading effect on protein solubilization in alfalfa hay.
FIG. 20 is a graph illustrating the effect of alfalfa hay concentration on protein solubilization.
FIG. 21 is a graph illustrating an examination of the repeatability of results for protein solubilization of soybean hay using lime.
FIG. 22 is a graph illustrating temperature effect on protein solubilization of soybean hay.
FIG. 23 is a graph illustrating lime loading effect of protein solubilization of soybean hay.
FIG. 24 is a graph illustrating the effect of soybean-hay concentration on protein solubilization.
FIG. 25 is a graph illustrating the reproducibility of off offal studies. Three runs were performed at identical operating conditions.
FIG. 26 is a graph illustrating a comparison of conversion at three different offal concentrations.
FIG. 27 is a graph illustrating a comparison of conversion for three different lime loadings.
FIG. 28 is a graph illustrating a comparison of conversion for two different temperatures.
FIG. 29 is a graph illustrating amino acid content of liquid product without additional treatment, and with treatment by 6N HCl.
FIG. 30 is a graph illustrating a comparison of amino acids present in raw material and dry treated solids. Because the treated solid was very wet (80% moisture) when removed from the reactor, some of the amino acids shows are derived from residual liquid product.
FIG. 31 is a graph illustrating a comparison of the amino acids present in the liquid phase after 30 minutes and after 2 hours in an experiment at 75° C., 0.075 g lime/g dry offal, and 60 g dry offal/L slurry.
FIG. 32 is a graph illustrating a comparison of the amino acids present in the liquid phase after 30 minutes and after 2 hours in an experiment at 75° C., 0.075 g lime/g dry offal, and 80 g dry offal/L slurry.
FIG. 33 is a graph illustrating a comparison of the amino acids in the centrifuged liquid phase after 30 minutes for three different initial offal concentrations (g dry offal/L slurry) at 75° C. and 0.075 g lime/g dry offal.
FIG. 34 is a graph illustrating a comparison of the amino acids present in the centrifuged liquid phase at different times as 75° C., 0.075 g lime/g dry offal, and 40 g dry offal/L slurry.
FIG. 35 illustrates a setup for generating amino acid-rich feather products using feathers and offal as raw materials. 1 is a non-centrifuges liquid. 2 is the centrifuged liquid after lime treatment. 3 is the residual solids after lime treatment. 4 is the centrifuged liquid after carbon dioxide bubbling. 5 is the final product.
FIG. 36 is a graph illustrating calcium concentration as a function of pH during precipitation through carbon dioxide bubbling (high initial pH).
FIG. 37 is a graph illustrating calcium concentration as a function of pH during precipitation with carbon dioxide bubbling (lower initial pH).
FIG. 38 is a graph illustrating the effect of air-dried hair concentration on protein solubilization.
FIG. 39 is a graph illustrating lime loading effect on protein solubilization of air-dried hair.
FIG. 40 is a graph illustrating lime loading effect on protein solubilization of air-dried hair in long-term treatments.
FIG. 41 is a graph illustrating ammonia, total Kjeldhal nitrogen, and estimated protein nitrogen concentration as a function of time in experiment A1.
FIG. 42 is a graph illustrating ammonia, total Kjeldhal nitrogen, and estimated protein nitrogen concentration as a function of time in experiment A2.
FIG. 43 is a graph illustrating ammonia, total Kjeldhal nitrogen, and estimated protein nitrogen concentration as a function of time in experiment A3.
FIG. 44 is a graph illustrating free amino acid concentration as a function of time in experiment A2.
FIG. 45 is a graph illustrating total amino acid concentration as a function of time in experiment A2.
FIG. 46 is a graph illustrating free amino acid concentration as a function of time in experiment A3.
FIG. 47 is a graph illustrating total amino acid concentration as a function of time in experiment A3.
FIG. 48 is a graph illustrating percent conversion of protein to the liquid phase as a function of time for hair hydrolysis with two steps in series.
FIG. 49 shows the mass balance of two-step and one-step lime treatment processes.
FIG. 50 is a graph illustrating repeatability of protein solubilization of shrimp head waste.
FIG. 51 is a graph illustrating temperature effect on protein solubilization of shrimp head waste.
FIG. 52 is a graph illustrating lime loading effect on protein solubilization of shrimp head waste.
FIG. 53 illustrates a single-stage solubilization process according to an embodiment of the present invention.



DETAILED DESCRIPTION
The present invention relates to a process for solubilizing protein from a biological source through hydrolysis. It also relates to devices for use in such solubilization and to a solubilization system.
Specific embodiments described hereafter relate to solubilization of protein from three different groups of biological sources. The first group includes recalcitrant or keratinous protein sources such as chicken feathers and animal hair. The second group includes labile or animal tissue protein sources such as chicken offal and shrimp heads. The third group includes plant protein sources such as soybean hay and alfalfa. Additional groups of protein sources and examples within the three groups above will be apparent to one skilled in the art.
The process generally involves application of an alkali such as lime (Ca(OH)2 or calcium hydroxide) to the protein source at a particular temperature. A liquid product is obtained with some solid residue. In specific embodiments described below in Table 1, process conditions suitable for each of the three source groups are provided.







TABLE 1







Suitable treatment conditions for solubilizing protein










Protein Source














Recalcitrant
Labile
Plant
















Temperature
100
75
100



(° C.)



Time (h)
4-8 (feathers)
0.25
2.5




16 (hair)



Lime Loading (g
0.1 (feathers)
0.075
0.05-0.075



Ca(OH)2/g
0.25 (hair)



material)



Concentration
100
60-80
60



(g material/L



slurry)










In certain embodiments of the invention, a well-insulated, stirred reactor is used to perform protein hydrolysis (solubilization) for different time periods, to obtain a liquid product rich in amino acids.
Although lime is used in some embodiments of the present invention, alternative alkalis such as magnesium oxide, magnesium hydroxide, sodium hydroxide, sodium carbonate, potassium hydroxide and ammonia may also be used in the present invention. However, most such alkalis may not be recovered by carbonation.
Lime also provides benefits over some other alkalis because it is poorly soluble in water. Due to its low solubility, lime maintains a relatively constant pH ( ̃12) for an aqueous solution, provided enough lime is in suspension in the solution. This ensures a constant pH during the thermo-chemical treatment and relatively weaker hydrolysis conditions (compared to sodium hydroxide and other strong bases), which may reduce the degradation of susceptible amino acids.
The thermo-chemical treatment of high-protein materials generates a mixture of small peptides and free amino acids. During the treatment, newly generated carboxylic acid ends of peptides or amino acids react in an alkaline medium to generate carboxylate ions, consuming lime or other alkali in the process.
During the protein hydrolysis, several side reactions occur. FIG. 1 shows a step-wise diagram for the hydrolysis of protein-rich material under alkaline conditions. Ammonia is generated as a by-product during amino acid degradation (e.g., deamidation of asparagine and glutamine, generating aspartate and glutamate as products). In some embodiments, this ammonia may be captured and neutralized with an acid, such as sulfuric acid, to produce ammonium salts. These salts may then be used as fertilizer or for other purposes.
Arginine, threonine and serine are also susceptible to degradation under alkaline conditions. The susceptibility of arginine and threonine to degradation of nutritional importance because both are essential amino acids. Reducing the contact time between the soluble peptides and amino acids with the alkaline medium decreases degradation and increases the nutritional quality of the final product. The use of low temperatures ( ̃100° C.) may also reduce and degradation.
A step-wise treatment of protein-rich materials may be used when long-term treatment times are required for high solubilization efficiencies (animal hair and chicken feathers). An initial product of better quality is obtained during the early treatment, whereas a lower quality product is generated thereafter. For example, a series of lime treatments may be used to obtain products with different characteristics when the initial waste is a mixture. For example, in an offal+feathers mixture, an initial treatment may target the hydrolysis of chicken offal, using low temperatures and short times, while a second lime treatment (longer time and higher temperature) may digest the feathers.
Table 2 summarizes the suitable conditions and effects of the different treatment variables (temperature, concentration, lime loading and time) on protein hydrolysis for different materials.







TABLE 2







Suitable conditions for thereto-chemical treatment of materials studied









Material
Notes
Recommended conditions





Alfalfa hay
Hydrolysis increases with temperature, and
0.075 g Ca(OH)2/g alfalfa,


(15.8% protein)
alfalfa hay concentration (up to 60 g/L).
100° C., 60 min, 60 g/L.



Lime loading has the least significant effect



but is required to convert protein into small



peptides and free amino acids. Suitable for



ruminants.


Soybean hay
Hydrolysis increases with lime loading and
0.05 g Ca(OH)2/g soybean,


(19% protein)
temperature (up to 100° C.), 100° C.
100° C., 150 min.



recommended because of lower energy



requirements. Soybean hay concentration



has no significant effect. The no-lime



experiment gives significantly lower



hydrolysis conversions. Suitable for



ruminants.


Shrimp head waste
Reaction is complete after 30 min.
0.05 Ca(OH)2/g dry shrimp,



Temperature has no significant effect.
at least 75° C., at least 15 min.



Hydrolysis increases with lime loading (up



to 0.05 g Ca(OH)2/g dry shrimp). Suitable



for monogastrics.


Offal
No significant change in conversion occurs
0.075 g Ca(OH)2/g dry offal,


(15% protein)
after 30 min. Offal concentration has no
75° C., at least 15 min.



significant effect. Hydrolysis increases with



lime loading (up to 0.1 g Ca(OH)2/g dry



offal). Suitable for monogastrics.


Offal + feathers
A two-step process was studied: Step 1
Step 1: 0.075 g Ca(OH)2/g dry offal,



targets the hydrolysis of offal and generates
50-100° C., 30 min.



a high-quality amino acid mixture. Step 2
Step 2: ~0.05 g Ca(OH)2/g feathers,



targets the hydrolysis of feathers and
100° C., 2-4 h.



generates a ruminant feed.


Feathers
Hydrolysis occurs faster than with hair,
0.1 g Ca(OH)2/g feathers,


(96% protein)
70% conversion obtained after 6 h. Suitable
100° C., 4-8 h.



for ruminants.


Hair
Long-term treatment required for high
Step 1: 0.25 g Ca(OH)2/g hair,


(92% protein)
protein hydrolysis. Two-step process
100° C., 8 h.



recommended for reducing amino acid
Step 2: ~0.25 g Ca(OH)2/g hair,



degradation. Suitable for ruminants.
100° C., 8 h.









The use of calcium hydroxide as the alkaline material in a process of the present invention produces a relatively high calcium concentration in the liquid product obtained from the reaction (also referred to as the “centrifuged solution” in some embodiments). Because some calcium salts have low solubility, calcium can be recovered by precipitating it as CaCO3, Ca(HCO3)2, or CaSO4. Calcium carbonate may be preferred because of its low solubility (0.0093 g/L, solubility product for CaCO3 is 8.7×10−9). In contrast, the solubility of CaSO4 is 1.06 g/L, with a solubility product of 6.1×10−5, and the solubility of Ca(HCO3)2 is 166 g/L, with a solubility product of 1.08. Also, it is easier to regenerate Ca(OH)2 from CaCO3 than from CaSO4.
Precipitation of calcium carbonate by bubbling CO2 into the reaction liquid product results in a calcium recovery between of 50 and 70%. A high pH in the reaction liquid product before calcium recovery may be recommended (>10) so that calcium carbonate and not calcium bicarbonate is formed during the process. A pH of 9 may also be sufficient in some embodiments. A final pH after recovery may be between  ̃8.8 and 9.0.
Proteins resulting from process of the present invention may have many uses, including use as animal feed. As a general rule, the soluble protein from recalcitrant and plant protein sources does not have a well-balanced amino acid profile. These proteins are accordingly best used as ruminant feed. In labile proteins, the amino acid profiles are well balanced, so the solubilized protein may also be used as feed for monogastric animals. Thus the end uses of the proteins solubilized by the present process may be indicated by the original source of such proteins. An additional benefit in animal feed uses may be the lack of prions in protein produced by some processes of the present invention. Lime treatment conditions are severe enough in many processes to substantially destroy prions, thereby improving the safety of any food produced using the solubilized proteins.
Additionally, in some embodiments the invention may include a holding step in which reaction liquid is heated to an elevated temperature for a certain time period to destroy all or a significant amount of prions that may be present in the liquid. For example, the liquid may be heated to a temperature of between 125-250° C. for between 1 second and 5 hours.
Protein-rich materials often found in waste may be subdivided into three categories: keratinous, animal tissue, and plant materials, each with different characteristics.
Animal hair and chicken feathers have high protein content ( ̃92% and  ̃96%, respectively), with some contaminants such as minerals, blood, and lipids from the slaughter process. The main component in animal hair and chicken feathers is keratin. Keratin is a mechanically durable and chemically unreactive protein, consistent with the physiological role it plays: providing a tough, fibrous matrix for the tissues in which it is found. In mammal hair, hoofs, horns and wool, keratin is present as α-keratin; and in bird feathers it is present as β-keratin. Keratin has a very low nutritional value; it contains large quantities of cysteine and has a very stable structure that render it difficult to digest by most proteolytic enzymes.
The behavior of chicken feathers and animal hair during some the thermo-chemical treatment processed of the present invention is presented in FIGS. 2 and 3. FIG. 22 shows a higher hydrolysis rate for chicken feathers than for animal hair, and a higher final conversion to digestible protein. This difference may be explained by the easier lime accessibility to a more extended conformation in β-keratin, or by the different macro structure present in animal hair when compared to chicken feathers (fibril structure, porosity, etc.). At least 8 hours is recommended for a high hair conversion at 100° C. with 0.1 g Ca(OH)2/g dry matter lime loading, but in the case of feathers, 70% conversion can be achieved in  ̃4 hours.
A linear relation between the reaction rate and conversion is found for both materials (FIG. 3), indicating a first order reaction rate for the alkaline hydrolysis of protein. A pseudo-equilibrium of hydrolysis vs. degradation is found at high conversions.
Animal tissue offers fewer digestive challenges than keratinous materials. Cells in animal tissues contain nuclei and other organelles in a fluid matrix (cytoplasm) bound by a simple plasma membrane. The plasma membrane breaks easily, liberating glycogen, protein, and other constituents for digestion by enzymes or chemicals.
Animal tissues (offal and shrimp heads) hydrolyze well in less than 15 minutes (FIG. 4) and do not require strong treatment conditions; low temperature, low lime loading, and short times are suitable. Lipids and other materials present in animal tissue consume lime more rapidly through side reactions such as lipid saponification, resulting in lower pH of the liquid product at the end of the process and making the liquid product susceptible to fermentation.
Shrimp heads and chicken offal are both animal protein by-products from the food industry. Because these are animal tissues, the amino acid distribution of the liquid product is expected to be similar to animal requirements, although quality may vary because the materials vary from batch to batch. Histidine may be the limiting amino acid in the liquid product.
Another specific use for the present process involves the disposal of dead birds in the poultry industry. For example, approximately 5% of chickens die before reaching the slaughterhouse. A typical chicken coop does not, however, have enough dead birds to process on site, so a method is needed to store the dead birds while the await pick up for processing. Using a process of the present invention, the dead birds can be pulverized with suitable equipment such as a hammer mill and lime may be added to raise the pH of the birds and prevent spoilage. The lime concentration may be approximately 0.1 g Ca(OH)2/dry g dead bird. When the lime-treated birds are collected and brought to a central processing plant, they may be heated to complete the protein solubilization process.
Finally, plants contain a difficult-to-digest lignocellulosic matrix in their the complex cell walls, rendering them more difficult to digest than animal tissue. However, the presence of highly water-soluble components results in a high initial conversion of protein into a liquid during some processes of the present invention. FIG. 5 compares the protein hydrolysis rates for soy bean and alfalfa hay. It shows a higher soluble fraction for soybean hay than alfalfa hay and a similar hydrolysis rate for both materials.
Lime treatment of these plant materials generates a product poor in lysine and threonine, which will decrease the nutritional value of the liquid product for mono-gastric animals.
In some embodiments of the invention in which the process is used to solubilize protein from plants, the resulting fiber in the solid residue is also more digestible because lignin and acetyl groups are removed. Lime treatment of plant materials may generate two products, a liquid product which is rich in protein (small peptides and amino acids from alkaline hydrolysis), and a solid residue rich in holocellulose that can be treated to reduce its crystallinity and increase its degradability. Thus there is an unexpected synergistic effect when some processes of the present invention are combined with plant digestion processes.
FIG. 6 shows a process for solubilization of protein in protein-containing materials. The process does not include lime recovery. In the process, the protein-containing material and lime are added to a reactor. In a specific embodiment, quick lime (CaO) is added so that the heat of its reaction creates the hydrated form, slake lime (Ca(OH)2) reduces further heat requirements of the reaction. The unreacted solids may be countercurrently washed to recover the solubilized protein trapped within the unreacted solids. The liquid product exiting the reactor contains the solubilized protein. An evaporator concentrates the solubilized protein by removing nearly all of the water. Preferably enough water may remain so that the concentrated protein is still pumpable.
Suitable evaporators include multi-effect evaporators or vapor-compression evaporators. Vapor compression may be accomplished using either mechanical compressors or jet ejectors. Because the pH is alkaline, any ammonia resulting from protein degradation will volatilize and enter the water returned to the reactor. Eventually the ammonia levels may build up to unacceptable levels. At that time a purge steam may be used to remove excess ammonia. The purged ammonia may be neutralized using an acid. If a carboxylic acid is used, (e.g. acetic, propionic or butyric acid), then the neutralized ammonia can be fed to ruminants as a nonprotein nitrogen source. If a mineral acid is added, the neutralized ammonia may be used as a fertilizer.
The concentrated protein slurry exiting the evaporator may be carbonated to react excess lime. In some applications, this concentrated slurry may be directly added to feeds provided that shipping distances are short. However, if shipping distances are long and a shelf-stable product is needed, the neutralized concentrated slurry may be spray dried to form a dry product. This dry product contains a high calcium concentration. Because many animals need calcium in their diet, the calcium in the solubilized protein may be a convenient method of providing their calcium requirement.
Referring now to FIG. 7, a similar process divided into two stages is illustrated. This process is suitable for protein-containing materials that have a mixture of proteins suitable for ruminant and monogastric feeds. For example, dead birds contain feathers (suitable for ruminants) and offal (suitable for monogastrics). The first stage of the process employs mild conditions that solubilize labile proteins, which may then be concentrated, neutralized and dried. These proteins may be fed to monogastrics. The second stage employs harsher conditions that solubilize the recalcitrant proteins, which may be concentrated, neutralized and dried. These proteins may be fed to ruminants.
FIG. 8 illustrates a process similar to that of FIG. 6, with an additional calcium recovery step to yield a low-calcium product. To recover calcium, the evaporation stage occurs in two steps. In the first evaporator, the proteins in the existing stream remain in solution. Carbon dioxide is added to precipitate the calcium carbonate. During this step the pH is preferably approximately 9. Addition of too much carbon dioxide results in a drop in pH favoring calcium bicarbonate formation. Because calcium bicarbonate is much more soluble than calcium carbonate, calcium recovery is reduced if this occurs. The calcium carbonate is recovered using a filter. The calcium carbonate may be countercurrently washed to recover soluble protein. The second evaporator then removes most of the remaining water. Enough water may be left so that the exiting slurry is pumpable. Finally, the slurry may be spray dried to form a shelf-stable product.
FIG. 9 shows the two-stage version of FIG. 8 which may be used to process protein sources that have a mixture of labile and recalcitrant proteins. The first stage solubilizes labile proteins that are suitable for monogastrics and the second stage solubilizes proteins that are suitable for ruminants.
FIG. 10 shows a single-stage continuous stirred tank reactor (CSTR) which is suitable for processing labile proteins. The solids exit the reactor using a screw conveyor that squeezes out liquid from solids.
FIG. 11 shows multi-stage CSTRs. Four stages are shown, which approximates a plug flow reactor. This reactor type is well suited for use with recalcitrant and plant protein sources. The plug flow behavior minimizes the amount of reacted feed that exits with spent solids. In this embodiment, the liquid flow is countercurrent to the solid flow.
FIG. 12 shows multi-state CSTRs in which the liquid flow is cocurrent to the solids flow.
FIG. 13 shows multi-stage CSTRs in which the liquid flow is crosscurrent to the solids flow.
FIG. 14 shows a true plug flow reactor which is well suited for recalcitrant and plant protein sources. Protein is fed into the reactor using appropriate solids equipment, such as a screw conveyor as shown in FIG. 14 or a V-ram pump, not shown. The reactor contains a central shaft that rotates “fingers” that agitate the contents. Stationary “fingers” are attached to the reactor wall to prevent the reactor contents from spinning unproductively. Water is passed countercurrently to the flow of solids. The water exiting the top of the reactor contains solubilized protein product. It exits through a screen to block solids. The fibrous nature of some protein sources such as chicken feathers, hair, and plants make their filtration easy. The unreacted solids at the bottom of the reactor are removed using a screw conveyor that squeezes liquids from the solids. In this embodiment, the squeezed liquid flows back into the reactor rather than through screen on the side of the screw conveyor. The object of such an arrangement is to have the solids exit as a tight plug so that the water added to the bottom of the reactor preferentially flow upward, rather than downward. Because the exiting solids were contacted just prior to exit with water entering the reactor, there is no need to countercurrently wash these solids.
FIG. 15 shows a plug flow reactor similar to the one shown in FIG. 14, except the exit screw conveyor is not connected to the center shaft of the reactor. This allows for mixing speed and conveyor speed to be independently controlled.
FIG. 16 shows a plug flow reactor similar to the one shown in FIG. 14, with the exception that solids exit through a lock hopper rather than a screw conveyor. To prevent air from entering the reactor, the lock hopper may be evacuated between cycles.
FIG. 53 shows a process for solubilization of protein in protein-containing materials. First, in an optional grinding step, the protein source is ground to increase its surface area. This increases the reaction rate in the reacting step. Once the protein is solubilized in a reactor, it begins to degrade, thus a faster reacting step may reduce the amount of degradation. A faster reaction rate may also increase the reaction product concentration, making it cheaper to recover. If a grinding step is used, it may be achieved using hammer mills, in-line homogenizers, or other suitable equipment.
Next the protein is reacted with an alkali at an elevated temperature and pH. The pH may fall between around 10 and 13, for example, it may be approximately 12. Any base may be used in this reaction step, but in selected embodiments the base is calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, sodium hydroxide, sodium carbonate, potassium hydroxide, or ammonia. Calcium oxide and calcium hydroxide are poorly soluble in water and thus may be recovered more easily. They also buffer pH to approximately 12. Further, calcium is a dietary nutrient and need to be removed from the final protein product. Other nutrient alkalis may also be left in the final protein product. General reaction conditions may be as described herein, for example, for different protein sources.
The reactor may be a stirred tank. It may be operated at 1 atm, although increased pressure may also be used, particularly with higher temperatures, to achieve faster reaction rates. Steam from other parts of the process may be used to maintain reactor temperature, for example by purging it directly into the reactor.
During the reaction, some amino acids decompose to ammonia. This ammonia will usually enter the gas phase. It may be neutralized with an appropriate acid, such as sulfuric acid, to form ammonia salts. These ammonia salts may then be used for fertilizer or other applications.
Next solids and liquids are separated in a stream exiting the reaction. This may be accomplished using a solid/liquid separator. The solids recovered may contain both reactive solids, such as unsolubilized protein, and inert solids, such as bones and rocks. Most inert solids have a higher density than reactive solids and that property may be exploited to aid separation. This step allows repetitive recycling of reactive solids, improving overall yield for the process. It also allows removal of inert solids whose presence can decrease the efficiency of the reaction step and the process overall.
Density separators that may be used to separate reactive and inert solids include settlers and hydroclones.
Next an optional hold step may occur. In this step, the liquid from the reaction step containing solubilized protein may be heated to an elevated temperature for a certain time period, then cooled. It is possible that the liquid may contain intact prions after the reaction step. These prions can present a health hazard to any animals that later consume the solubilized proteins and also to humans. However, the heating during the hold stem may be sufficient to destroy all or a significant portion of any prions present in liquid. This hold step may be similar to pasteurization. For different types of prions, appropriate temperatures and holding times may vary. In most cases there will be a variety of temperature and holding time combinations sufficient to achieve prion destruction. In specific embodiments, the holding step conditions may be selected so as to achieved a desired level of prion destruction, but also to simultaneously limit amino acid degradation. For example, the hold step temperature may be between 125-250° C. The holding time may be between 1 second and 5 hours. In order to select the most appropriate holding step conditions, prions likely to occur in the protein source may be previously identified.
The holding step may be heated by steam. The system may include a heat exchange element to allow heat from liquid leaving the holding step to be used to help warm liquid entering it.
The liquid may then be neutralized with an acid to reduce the pH to between 2 and 9. The acid used for this step may be nearly any acid or acid source. In specific embodiments, it may be carbon dioxide, phosphoric acid, carboxylic acids, such as acetic acid, propionic acid, and butyric acid, lactic acid, sulfuric acid, nitric acid, and hydrochloric acid.
Carbon dioxide may be used as an acid source particularly when the alkali contained calcium. Carbon dioxide is inexpensive and creates calcium carbonate or bicarbonate, depending on the pH, during neutralization of the calcium-containing reaction liquid. Both calcium carbonate and bicarbonate may be converted back to lime using a lime kiln. This lime may be reused in the reaction step.
Because carbon dioxide is a gas, it can cause the liquid to foam during neutralization. To avoid this problem, the carbon dioxide may be transferred into the liquid phase using a microporous, hydrophobic membrane, such as a membrane made by Celgard LLC (North Carolina).
Phosphoric acid is used in another particular embodiment when the reaction liquid contains calcium because the calcium phosphate formed is an important mineral in bone formation. Thus, it is a useful addition to the ultimate protein product.
In another embodiment, organic acids such as carboxylic acids and lactic acid may be used to neutralize liquid containing any alkali. Organic acids are a useful addition to the final protein product because they are an energy source for animals.
After neutralization, an optional solid/liquid separation may occur. This step may be most useful when the acid neutralization produces an insoluble salt, such as calcium carbonate, calcium bicarbonate, calcium sulfate or calcium phosphate. While some these materials may be desired in the final product, some may not, or it may be desirable to reduce their concentration in the final product. A solid/liquid separator may be used to remove all or part of the solids from the neutralized liquid. Suitable solid/liquid separators may include a filter press, a rotary drum filter and a hydroclone.
In one particular embodiment, neutralization of reaction liquid containing calcium via carbonation occurs at a pH of approximately 9. This allows substantial removal of calcium in the form of highly insoluble calcium carbonate via a solid/liquid separator. After a significant amount of calcium carbonate is removed, then carbonation or other neutralization may continue to reduce the pH further.
After neutralization and optional solid separation, the neutralized liquid may be concentrated. The reaction liquid typically has between 2-6% solubilized protein. This concentration is likely not significantly affected by the holding, neutralization and solid recovery steps. After concentration, the concentrated liquid may have between 35-65% solubilized protein.
Concentration may be achieved by evaporation. For example, multi-effect, mechanical vapor-compression, and jet ejector vapor compression evaporation may be used to removed water from the neutralized liquid. In general, dilute protein solutions tend to foam while concentrated ones do not. As a result, if the evaporators are operated using liquid containing at least 15% solubilized protein, foaming is reduced. Additionally, particularly for more dilute liquid, an antifoaming agent may be added to the liquid. Vegetable oils are effective antifoaming agents and add an energy component to the final protein product.
Filtration may also be used to concentrate the neutralized liquid. Specifically, a dilute solution may be concentrated by water permeation through an appropriate membrane, such as a reverse osmosis or tight nanofiltration membrane. To minimize concentration polarization, an oscillatory disk filter (e.g. VESP) may be used to achieve high permeation rates and high product concentrations.
The neutralized liquid may also be concentrated by freezing. As ice crystals form, protein is largely excluded, resulting in a separation of nearly pure frozen water and a concentration amino acid/polypeptide solution. The ice crystals may be washed, for example countercurrently, to remove concentrated product from their surface.
Water may also be extracted from the neutralized liquid using various immiscible amines, such as di-isopropyl amine, trimethyl amine, methyl diethyl amine, and other amines.
The water removed during the concentration step may be returned to the reaction step. It may be heated prior to its return via heat exchange with process steam or other warm fluid from other parts of the process. If the water from the concentration step is too hot for the reaction step, it may also be heat exchanged with a cooler fluid to bring it to an appropriate temperature before addition to the reaction.
The concentrated liquid may optionally be dried. Drying may be achieved using standard equipment such as spray driers or scraped drum driers. Scraped drum driers may produce a final solid with a high bulk density. Additionally, steam from these driers may be recovered and used for process heat, such as heating the reactor.
The process of FIG. 53 may thus be performed in a system having an optional grinder, a reactor, an ammonia collector, a solid/liquid separator, an optional density separator, an optional holding tank, a neutralization tank, another optional solid/liquid separator, a concentration tank, and an optional drier. These components may be connected to one another so as to allow processing of the protein source to liquid concentrate or dry product. Return loops may be included to allow further processing and/or reuse as needed. Heat exchangers to adjust temperature and allow reuse of process heat may also be included.
It will be readily understood that the conditions, machinery and other components of the systems and processes of the present invention may be interchanged with one another to produce variant protein solubilization processes and systems. For example, components described for one system or process may be used with another to digest a particular protein, achieve a desired product composition, aid in recycling and heat recovery, and to facilitate interchangeability between different systems.
EXAMPLES
The following examples are presented to illustrate and further describe selected embodiments of the present invention. They are not intended to literally represent the entire breadth of the invention. Variations upon these examples will be apparent to one skilled in the art and are also encompassed by the present invention.
In these Examples, equation and experiment numbers are intended to refer to equations and experiments within the indicated example only. Equations and experiments are not consecutively or similarly numbered among different examples.
Example 1
General Methods and Equipment
The following general methods and equations were used in the present examples:
The concentration of the different compounds in the liquid product and in raw materials was determined by two different procedures: Amino acid composition was determined by HPLC measurements (performed by the Laboratory of Protein Chemistry of Texas A&M University); total Kjeldhal nitrogen and mineral determinations were performed by the Extension Soil, Water and Forage Testing Laboratory of Texas A&M University using standard methodologies.
Measurement of digestibility of lignocellulosic material was done by the 3-d digestibility test using the DNS method. Biomass was ground to an adequate size if necessary. A Thomas-Wiley laboratory mill with several sieve sizes located in the Forest Science Research Center was used.
Lignin, cellulose, hemicellulose (holocellulose), ash, and moisture content of materials were determined using NREL methods.
Water baths and shaking air baths with thermocouples for temperature measurement and maintenance were used when required. Heating was also accomplished by tape and band heaters. Water and ice baths were used as cooling systems.
In general, the experiments in these examples were performed in a 1-L autoclave reactor with a temperature controller and a mixer powered by a variable-speed motor (FIG. 17). This reactor was pressurized with N2 to obtain samples through the sampling port. A high mixing rate ( ̃1000 rpm) was used to induce good contact between the suspended solids and the liquid.
Treatment conditions (for several organic materials) were systematically varied to explore the effect of the process variables—temperature, time, raw material concentration (g dry material/L), and calcium hydroxide loading (g Ca(OH)2/g dry material)—on the protein hydrolysis. Samples were taken from the reactor at different times and centrifuged to separate the liquid phase from the residual solid material.
Equation 1 was used the conversion of the centrifuged sample, based on the initial Total Kjeldhal Nitrogen (TKN) of the organic material:




  
    
      
        
          Conv
          1
        
        =
        
          
            
              V
              water
            
            ×
            
              TKN
              
                centrifuged
                ⁢
                
                  
                
                ⁢
                liquid
              
            
          
          
            
              m
              
                dry
                ⁢
                
                  
                
                ⁢
                sample
              
            
            ×
            
              TKN
              
                dry
                ⁢
                
                  
                
                ⁢
                sample
              
            
          
        
      
    
    
      
        (
        1
        )
      
    
  




The liquid product was analyzed using two different methods to obtain the amino acid concentrations and the conversion of the reaction. The first method determined the total nitrogen content of the liquid sample using the modified micro-Kjeldhal method. Multiplication of nitrogen content (TKN) by 6.25 estimates the crude protein content. The second method used an HPLC to obtain the concentration of individual amino acids present in the sample. In this procedure, the sample was treated with hydrochloric acid (150° C., 1.5 h or 100° C., 24 h) to convert proteins and polypeptides into amino acids; this measurement is called Total Amino Acid Composition. The HPLC determination without the initial hydrolysis with HCl determines the Free Amino Acid composition.
Additional measurements included: final pH of liquid product, mass of soluble matter in the centrifuged liquid after evaporating water at 45° C., and mass of residual solid after drying at 105° C. This final measurement, the mass of residual solids, was determined by filtering the final mixture through a screen without further washing with water. The retained solids were dried at 105° C. The dry weight included not only the insoluble solids, but also soluble solids that were retained dissolved in residual solids.
Example 2
Protein Solubilization in Alfalfa Hay
Alfalfa hay is commonly used in ruminant nutrition. Higher feed digestibility ensures that animal requirements will be satisfied with less feed. Treatment of alfalfa hay generates two separate products: a highly digestible soluble fraction found in the liquid product, and a delignified residual solid.
Alfalfa hay was treated with calcium hydroxide, the least expensive base on the market. In Table 3, the composition of alfalfa in different states is summarized.







TABLE 3







Composition of alfalfa in its different states (McDonald et al., 1995)












Alfalfa

Crude


Hemi-


(% of dry mass)
Soluble
protein
Lignin
Cellulose
cellulose















Fresh early bloom
60
19
7
23
2.9


Mid bloom
54
18.3
9
26
2.6


Full bloom
48
14
10
27
2.1


Hay, sun-cured,
58
18
8
24
2.7


early bloom


Mid bloom
54
17
9
26
2.6


Late bloom
48
14
12
26
2.2


Mature bloom
42
12.9
14
29
2.2









Sun-cured alfalfa hay was obtained from the Producers Cooperative in Bryan, Tex.; then it was ground using a Thomas-Wiley laboratory mill (Arthur H. Thomas Company, Philadelphia, P A) and sieved through a 40-mesh screen. The moisture content, the total Kjeldhal nitrogen (estimate of the protein fraction), and the amino acid content were determined to characterize the starting material.
Raw alfalfa hay was 89.92% dry material and 10.08% moisture (Table 4). The TKN was 2.534% corresponding to a crude protein concentration in dry alfalfa of about 15.84% (Table 5). The remaining 84.16% corresponds to fiber, sugars, minerals and others. The amino acid composition for raw alfalfa hay is given in Table 6. The starting material contained a relatively well-balanced amino acid content (Table 6), with low levels of tyrosine.







TABLE 4







Moisture content of raw alfalfa hay













Solid
Dry solid
Dry Solid



Sample
(g)
(g)
(%)







1
7.1436
6.4248
89.94



2
5.9935
5.3884
89.90





Average
89.92

















TABLE 5







Protein and mineral content of raw alfalfa hay


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















1
2.5492
0.2
2.27
1.8383
0.4591
6508
16
90
6
45


2
2.5181
0.2
2.16
17.865
0.4321
6176
16
94
5
42


Mean
2.5336
0.2
2.215
1.8124
0.4456
6342
16
92
5.5
43.5
















TABLE 6







Amino acid composition of air-dried alfalfa hay












Amino acid
Measured
Amino acid
Measured
















ASP
14.44
TYR
2.94



GLU
11.85
VAL
5.61



SER
6.13
MET
1.01



HIS
1.39
PHE
5.59



GLY
5.30
ILE
4.40



THR
4.95
LEU
10.06



ALA
5.63
LYS
5.77



CYS
ND
TRP
ND



ARG
5.58
PRO
9.35







ND: Not determined



Values in g AA/100 g total amino acids.






Experiment 1.
Temperature Effect
To determine the effect of temperature on solubilizing protein in alfalfa hay, experiments were run at different temperatures keeping the lime loading and alfalfa concentration constant (0.075 g lime/g alfalfa and 60 g dry alfalfa/L respectively). The experimental conditions studied and variables measured are summarized in Table 7.







TABLE 7







Experimental conditions and variables measured to determine the effect


of temperature in protein solubilization of alfalfa hay









Temperature (° C.)













50
75
90
100
115
















Mass of alfalfa
56.7
53.4
56.7
56.7
56.7


(g)


Volume of
850
800
850
850
850


water (mL)


Mass of lime
4.3
4.0
4.3
4.3
4.3


(g)


Initial
50.3
73.2
94.1
93.1
105


temperature


(° C.)


pH final
11.1
11.3
10.7
9.9
9.85


Residual solid
39.5
34.9
37
36.8
35


(g)


Dissolved
2.6024
3.549
3.4995
3.6248
3.1551


solids in 100


mL (g)


Protein in 100
0.346
0.390
0.355
0.338
0.328


mL (g)


Protein
13.3
11.0
10.1
9.3
10.4


concentration


(%)









Table 8 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different temperatures. On the basis of the average TKN for dry alfalfa (2.53%), protein hydrolysis conversions were estimated (Table 9).







TABLE 8







Total Kjeldhal nitrogen content in the centrifuged liquid phase as a


function of time for Experiment 1 (alfalfa hay)









Temperature












Time (min)
50° C.
75° C.
90° C.
100° C.
115° C.















0
0.0506
0.0503
0.0526
0.0576
0.0474


5
0.0520
0.0669
0.0609
0.0641
0.0620


10
—
0.0640
—
—
—


15
0.0609
0.0653
0.0637
0.0713
0.0756


30
0.0665
0.0655
0.0679
0.0813
0.0813


45
0.0692
0.0771
0.0719
0.0958
0.0955


60
0.0679
0.0771
0.0761
0.1039
0.0927


120
—
0.0778
—
—
—


150
0.0554
—
0.0568
0.0540
0.0525


180
—
0.0624
—
—
—





TKN in g nitrogen/100 g liquid sample.













TABLE 9







Percentage conversion of the total TKN to soluble


TKN for Experiment 1 (alfalfa hay)









Temperature












Time (min)
50° C.
75° C.
90° C.
100° C.
115° C.















0
33.5
33.3
34.8
38.2
31.4


5
34.4
44.3
40.3
42.5
41.1


10
—
42.4
—
—
—


15
40.3
43.2
42.2
47.2
50.1


30
44.0
43.4
45.0
53.9
53.9


45
45.8
51.0
47.6
63.5
63.3


60
45.0
51.0
50.4
68.8
61.4


120
—
51.5
—
—
—


150
36.7
—
37.6
35.8
34.8


180
—
41.3
—
—
—









The final product of protein hydrolysis is individual amino acids, which react with the hydroxyl, consume lime, and decrease the pH. This explains the lower pH obtained for high protein conversions (Tables 7 and 9).
The similar initial conversion for all temperatures can be explained by the high fraction of soluble components in alfalfa (approximately 50%, see Table 3). The final conversion, lower than the rest, is explained by the different sampling method. All early samples were taken from the reactor through the sampling port at the internal temperature. For the final sample, the fluid was cooled down to 35° C., the nitrogen pressure was released and the solids were filtered before the sample was taken. The sampling procedure for the final sample was altered to measure more variables. This same procedure was followed for the other experiments.
Highly soluble alfalfa components are present in the dissolved solids. Table 7 shows that at 75° C., the protein concentration in the solid remaining after liquid evaporation is approximately 11%. Although, this is actually lower than the protein content in the raw alfalfa, the processing steps convert protein into highly digestible amino acids, and these amino acids are mixed with other highly digestible alfalfa components increasing the nutritional value of the final product.
FIG. 18 presents the protein hydrolysis (percent conversion) as a function of time for the different temperatures studied. The conversion increases at higher temperatures. The conversion for 100° C. is similar to the one obtained at 115° C.; therefore, the lower temperature is favored because the amino acids should degrade less, the energy required is less, and the working pressure is lower.
Experiment 2.
Lime Loading Effect
To determine the effect of lime loading on protein solubilization of alfalfa hay, experiments were run at different lime/alfalfa ratios keeping the temperature and alfalfa concentration constant (75° C. and 40 g dry alfalfa/L respectively). The experimental conditions studied and variables measured are summarized in Table 10.







TABLE 10







Experimental conditions and variables measured to determine the lime loading effect


in protein solubilization of alfalfa hay









Lime loading (g lime/g alfalfa)














0
0.05
0.075
0.1
0.2
0.4

















Mass of alfalfa (g)
37.8
37.8
37.8
37.8
37.8
37.8


Volume of water (mL)
850
850
850
850
850
850


Mass of lime (g)
0
1.9
2.9
3.8
7.6
15.2


Temperature (° C.)
75
75
75
75
75
75


Initial Temperature (° C.)
78.1
71.2
78.2
58.3
80.3
81.5


pH final
5.7
10
10.7
—
11.4
11.2


Residual solid (g)
23.5
24.1
22.8
20.3
23.7
29.5


Dissolved solids in 100 mL (g)
1.3489
1.8645
2.0201
1.9289
1.9215
2.1651


Protein in 100 mL (g)
0.286
0.249
0.231
0.267
0.264
0.251









Table 11 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different temperatures.







TABLE 11







Total Kjeldhal nitrogen content in the centrifuged liquid


phase as a function of time for Experiment 2 (alfalfa hay)









Lime loading













Time (min)
0 g/g
0.05 g/g
0.075 g/g
0.1 g/g
0.2 g/g
0.4 g/g
















0
0.0360
0.0364
0.0353
0.0370
0.0319
0.0345


5
0.0401
0.0394
0.0370
0.0392
0.0394
0.0373


15
0.0457
0.0423
0.0377
0.0427
0.0423
0.0401


30
0.0457
0.0452
0.0451
0.0441
0.0423
0.0450


45
0.0485
0.0466
0.0488
0.0462
0.0481
0.0457


60
0.0485
0.0511
0.0510
0.0478
0.0481
0.0498


150
0.0457
0.0394
0.0370
0.0427
0.0554
0.0401





TKN in g nitrogen/100 g liquid sample.






On the basis of the average TKN for dry alfalfa hay (2.53%), the protein hydrolysis conversions were estimated and are given in Table 12.







TABLE 12







Percentage conversion of the total TKN to soluble TKN for


Experiment 2 (alfalfa hay)









Lime loading













Time (min)
0 g/g
0.05 g/g
0.075 g/g
0.1 g/g
0.2 g/g
0.4 g/g
















0
35.7
36.1
35.0
36.7
31.6
34.2


5
39.8
39.1
36.7
38.9
39.1
37.0


15
45.3
41.9
37.4
42.3
41.9
39.8


30
45.3
44.8
44.7
43.7
41.9
44.6


45
48.1
46.2
48.4
45.8
47.7
45.3


60
48.1
50.7
50.6
47.4
47.7
49.4


150
45.3
39.1
36.7
42.3
54.9
39.8









Again, the initial conversions are similar for all lime loadings because of the highly soluble components present in the alfalfa (approximately 50%, see Table 3). The final conversion (150 min) for the experiment at 0.2 g lime/g alfalfa differed from the others because it increased whereas the others decreased. In the case of 0.2 g lime/g alfalfa, the final sample was taken through the sampling port, whereas the final sample for the other loadings was taken by opening the reactor and removing the sample.
FIG. 19 presents the protein solubilized (percent conversion) as a function of time for the different lime loadings studied. The conversion is similar for all lime loadings, even for the experiment with no lime. This behavior is related to the highly soluble contents in the alfalfa hay.
In the no-lime experiment, there is soluble protein present in the water phase; however, hydroxyl groups are dilute so no reaction occurred in the solid phase or the solid-liquid interface. A smaller amount of free amino acids were present because the hydrolysis reaction is likely to be slower under these conditions. The final pH was 5.7; likely, the pH became acidic because of acids (e.g., acetyl groups) released from the biomass and from amino acids released from the proteins. Because no lime was used, the concentration of dissolved solids was lower. In all the other cases, in Table 10, lime was a portion of the dissolved solids.
FIG. 19 shows that lime loading has no significant effect on the protein solubilization of alfalfa hay. A minimum lime loading might be recommended to avoid acid hydrolysis of protein, which tends to be more damaging than alkaline hydrolysis. This lime loading would result in a higher concentration of free amino acids in the liquid product.
Experiment 3.
Alfalfa Concentration Effect
To determine the effect of the initial alfalfa concentration on protein solubilization of alfalfa hay, experiments were run at different alfalfa concentrations keeping the temperature and lime loading constant (75° C. and 0.075 g lime/g alfalfa respectively). The experimental conditions studied and variables measured are summarized in Table 13.







TABLE 13







Experimental conditions and variables measured for determining


the effect of initial alfalfa concentration in protein solubilization









Alfalfa concentration (g dry alfalfa/L)












20
40
60
80















Mass of alfalfa (g)
18.9
37.8
53.4
75.6


Volume of water (mL)
850
850
800
850


Mass of lime (g)
1.5
2.9
4.0
5.7


Temperature (° C.)
75
75
75
75


Initial temperature (° C.)
78.1
78.2
73.2
82.1


pH final
10.7
10.7
11.3
11


Residual solid (g)
9.7
22.8
34.9
53.3


Dissolved solids in
1.0072
2.0201
3.549
4.1349


100 mL (g)


Protein in 100 mL(g)
0.154
0.231
0.390
0.450









Table 14 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different alfalfa concentrations. On the basis of the average TKN for dry alfalfa (2.53%), the protein hydrolysis conversions were estimated and are given in Table 15.







TABLE 14







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 3 (alfalfa hay)










Alfalfa concentration












Time (min)
20 g/L
40 g/L
60 g/L
80 g/L














0
0.0175
0.0353
0.0503
0.0514


5
0.0182
0.0370
0.0669
0.0571


10
—
—
0.0640
—


15
0.0204
0.0377
0.0653
0.0770


30
0.0211
0.0451
0.0655
0.0727


45
0.0218
0.0488
0.0771
0.0946


60
0.0218
0.0510
0.0771
0.0883


120
—
—
0.0778
—


150
0.0247
0.0370
—
0.0720


180
—
—
0.0624
—





TKN in g nitrogen/100 g liquid sample.













TABLE 15







Percentage conversion of the total TKN to soluble TKN


for Experiment 3 (alfalfa hay)










Alfalfa concentration












Time (min)
20 g/L
40 g/L
60 g/L
80 g/L














0
34.6
35.0
33.3
25.6


5
36.0
36.7
44.3
28.4


10
—
—
42.4
—


15
40.4
37.4
43.2
38.3


30
41.8
44.7
43.4
36.2


45
43.1
48.4
51.0
47.1


60
43.1
50.6
51.0
44.0


120
—
—
51.5
—


150
48.9
36.7
—
35.8


180
—
—
41.3
—









The final conversion (150 min) for the experiment at 20 g alfalfa/L differed from the others because it increased whereas the others decreased. In the case of 20 g alfalfa/L, the final sample was taken through the sampling port, whereas the final sample for the other concentrations was taken by opening the reactor and removing the sample.
FIG. 20 presents the protein solubilization (percent conversion) as a function of time for the different alfalfa concentrations studied. The conversion increases as alfalfa concentration increases, until it reaches a maximum between 60 and 80 g/L; at this point, because the mass of lime and alfalfa is very high, it was difficult for the alfalfa to contact the liquid phase, which decreased the conversion. The conversions for 80 g/L are similar to the ones obtained for 20 g/L. Also, the conversions for 40 and 60 g/L are similar. As Table 13 shows, the dissolved solids are higher for the higher alfalfa concentration.
Experiment 4.
Statistical Analysis
To determine if relationships are present between the variables studied in the protein solubilization of alfalfa hay, an additional 23 factorial experiment was run, using temperature, lime loading, and alfalfa loading as variables, and the TKN solubilization (conversion) at 60 minutes as the response variable. The conditions studied are summarized in Table 16, as well as the conversion obtained for each experiment.







TABLE 16







Experimental conditions studied in the 23 factorial experimental design














Var 3




Var 1
Var 2
Alfalfa
Y



Temperature
Lime loading
concentration
Conversion


Condition
(° C.)
(g lime/g solid)
(g/L)
(%)














1
75
0.075
40
50.6


2
100
0.075
40
53.9


3
75
0.1
40
47.4


4
100
0.1
40
58.6


5
75
0.075
60
51.0


6
100
0.075
60
68.8


7
75
0.1
60
60.4


8
100
0.1
60
67.3









Using the response variable, a Yates algorithm was performed with the conversion values to obtain the mean, the variable effect, and the interaction between the studied variables. This information is summarized in Table 17. To determine the variability of the measurement, Conditions I and 5 were repeated in triplicate (Table 18).







TABLE 17







Yates algorithm results (Milton and Arnold, 1990)














Yates
Interpretation


Column 1
Column 2
Column 3
Results
of Yates Results














104.49
210.48
458.00
57.25
Mean


105.98
247.52
39.32
9.83
E1 (Effect of Variable 1)


119.87
14.58
9.27
2.32
E2 (Effect of Variable 2)


127.65
24.74
−3.00
−0.75
I12 (Interaction of






Variables 1 and 2)


3.37
1.49
37.04
9.26
E3 (Effect of Variable 3)


11.20
7.78
10.16
2.54
I13 (Interaction of






Variables 1 and 3)


17.79
7.83
6.29
1.57
I23 (Interaction of






Variables 2 and 3)


6.96
−10.83
−18.66
−4.67
I123 (Interaction of






Variables 1, 2 and 3)
















TABLE 18







Standard deviation calculations and results











Condition
First rep.
Second rep.
Third rep.
Mean














5
54.68
47.66
51.04
51.13


1
51.95
50.56
55.12
52.55



S2
8.891
SE
1.491









In Table 18, the variance (S2) was calculated as the mean variance of both conditions studied. Then SE, standard deviation of variable effects, was estimated with the mean variance for four values (the effect and interactions in a 23 factorial are the mean value of four calculations). Given four degrees of freedom and 99% confidence, the t-student value is 3.747. Then, multiplying this t-value by SE (1.491) gives the limits of non-significant effects in the Yates results column (−5.59 and 5.59).
From Table 17, the only significant effects are the ones from Variable 1 (temperature, E1=9.83>5.59) and Variable 3 (alfalfa concentration, E3=9.26>5.59). This is consistent with the observations made in Experiments 1 and 3. From the values obtained in the factorial design, the presence of non-significant variable interactions implies that the effect of temperature and alfalfa concentration are additive, giving the highest conversion when both variables are high. This analysis cannot be readily extrapolated to higher temperatures and concentrations (as seen from Experiment 3), because different phenomena can occur at other conditions.
There is no significant effect of lime loading on the solubilization of protein from alfalfa hay (E2=2.32<5.59), and this variable does not interact with the other variables (I12 and I23<5.59); therefore, the lime loading may be based solely on preventing acid hydrolysis of protein to amino acids, rather than protein solubilization. The conversion only represents the presence of nitrogen (protein) in the liquid product, not individual hydrolyzed amino acids.
A comparison between the compositions of the raw material and the residual solid gives information on the effectiveness of lime treating alfalfa for protein solubilization. The composition for both materials is shown in Table 19. These results were obtained for Condition 5 of the factorial design (75° C., 0.075 g lime/g alfalfa and 60 g alfalfa/L).







TABLE 19







Comparison of protein and minerals content present in the raw alfalfa hay


and the residual solid after lime treatment


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(%)
(%)
(%)
(%)
(%)




















Dry
2.5336
0.20
2.21
1.8124
0.4456
5342
16
92
5.5
43.5


Alfalfa


Residual
2.2383
0.18
1.42
3.3554
0.4166
3969
71
137
17
37


Solid









Table 19 shows that the calcium concentration of the residual solids is greater than in the raw alfalfa. This value increases due to the lime added for the treatment, which is not completely soluble in water. The values for potassium and sodium decrease during the lime treatment due to the high solubility of these salts. The nitrogen present in the residual solid is similar to the value obtained for the raw material before lime treatment. This implies that the concentration of nitrogen in the solubles is similar to the concentration in the raw material.
The fraction of alfalfa that was solubilized in Condition 5 was calculated as follows:

soluble fraction=1−{32.5 g residual solids−[(3.55 g dissolved solids/100 mL liquid)*200 mL moisture]}/53.4 g initial alfalfa=0.524 g solubilized/g of alfalfa.

This calculation corrects for the dissolved solids contained in the 200 mL of liquid. This value (0.524 g solubilized/g alfalfa) is reported in Table 20.







TABLE 20





Variables measured for Condition 5


















Mass of alfalfa (g)
53.4
pH final
11.3


Volume of water (mL)
800
Residual solid (g)
32.5


Mass of lime (g)
4.0
Dissolved solids in 100 mL (g)
3.55


Temperature (° C.)
75
Soluble fraction of alfalfa
0.524









Experiment 5.
Amino Acid Analysis
Alfalfa hay was treated with lime for 60 min and 24 h with the recommended conditions: 100° C., 0.075 g lime/g alfalfa and 60 g alfalfa/L. The amino acid analysis was performed in three different ways:

    
    
        1) Centrifuged liquid product-Free amino acid analysis. The analysis was made without extra HCl hydrolysis of the sample. No amino acids were destroyed by the analytical procedure, but soluble polypeptides are missed in the analysis.
        2) Centrifuged liquid product-Total amino acid analysis. The analysis was made with 24-h HCl hydrolysis of the liquid sample. Some amino acids were destroyed by the analytical procedure or converted to other amino acids; soluble polypeptides are measured in the analysis.
        3) Dry product after evaporating water from the centrifuged liquid. Because this sample was solid, HCL hydrolysis was required. Some amino acids (asparagine, glutamine, and tryptophan) were destroyed by the acid and could not be measured.
    
    


Tables 21 and 22 show the free ammo acids and the total amino acids concentration for lime treated alfalfa at 60 min and 24 h, respectively. Table 23 shows the protein and mineral content for both samples.







TABLE 21







Free and total amino acid concentration for the centrifuged


liquid product of lime-hydrolyzed alfalfa hay at 60 min










Non hydrolyzed-free




amino acids
Hydrolyzed-total amino acids












Concentration
Percentage
Concentration
Percentage


Amino acid
(mg/L)
(%)
(mg/L)
(%)














ASN
165.87
17.17
0.00
0.00


GLN
0.00
0.00
0.00
0.00


ASP
54.30
5.62
334.81
23.04


GLU
109.11
11.29
155.35
10.69


SER
44.87
4.64
78.72
5.42


HIS
0.00
0.00
0.00
0.00


GLY
44.50
4.61
86.83
5.98


THR
18.97
1.96
43.65
3.00


ALA
37.34
3.87
76.42
5.26


ARG
77.27
8.00
110.28
7.59


TYR
0.00
0.00
18.68
1.29


CYS
36.57
3.79
ND
0.00


VAL
39.31
4.07
71.03
4.89


MET
4.68
0.48
0.00
0.00


PHE
9.20
0.95
47.82
3.29


ILE
22.62
2.34
39.62
2.73


LEU
27.35
2.83
64.06
4.41


LYS
5.58
0.58
31.22
2.15


TRP
18.81
1.95
ND
0.00


PRO
249.78
25.85
294.47
20.27


Total
966.15
100
1452.95
100
















TABLE 22







Free and total amino acid concentration for the centrifuged


liquid product from lime-hydrolyzed alfalfa hay at 24 h










Non hydrolyzed-free




amino acids
Hydrolyzed-total amino acids












Concentration
Percentage
Concentration
Percentage


Amino acid
(mg/L)
(%)
(mg/L)
(%)














ASN
76.10
8.07
0.00
0.00


GLN
0.00
0.00
0.00
0.00


ASP
70.26
7.45
239.79
17.51


GLU
116.33
12.33
157.16
11.47


SER
38.93
4.13
76.64
5.59


HIS
0.00
0.00
0.00
0.00


GLY
96.01
10.18
141.65
10.34


THR
9.48
1.00
37.28
2.72


ALA
37.19
3.94
74.06
5.41


ARG
75.25
7.98
93.55
6.83


TYR
0.00
0.00
8.43
0.62


CYS
35.66
3.78
ND
0.00


VAL
38.89
4.12
66.17
4.83


MET
0.00
0.00
0.00
0.00


PHE
10.48
1.11
48.45
3.54


ILE
21.90
2.32
39.84
2.91


LEU
25.95
2.75
60.90
4.45


LYS
0.00
0.00
26.76
1.95


TRP
17.56
1.86
ND
0.00


PRO
273.28
28.97
299.16
21.84


Total
943.24
100.00
1369.82
100.00
















TABLE 23







Comparison of protein and minerals content present in the centrifuged


liquid of lime-treatment of alfalfa hay


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)





60 min
0.0742
0.0062
0.149
0.2342
0.027
538
2
4
0
2


24 h
0.0926
0.0082
0.155
0.2342
0.031
518
2
6
0
2









For all the experiments, the centrifuged liquid contained a very high concentration of suspended particulate matter that might be measured in the Kjeldhal determination but not in the amino acid analysis. This explains the difference between the amino acid determination and the estimated protein concentration using Kjeldhal analysis (1.45 vs. 4.64 and 1.37 vs. 5.79 g protein/L).
A comparison of Tables 21-23 shows that although the nitrogen concentration increases from 60 min to 24 h, the total amino concentration remains relatively constant, so there is no need for a long treatment in the hydrolysis of alfalfa hay.
Finally, the amino acid composition of the products was compared to the needed essential amino acids of various domestic animals.
Table 24 shows the amino acid composition of dry product and liquid product (both free amino acids and total amino acids—Table 21). The amino acid composition of lime-hydrolyzed alfalfa hay at 60 min is not well balanced with respect to the essential amino acid requirements of different monogastric domestic animals. There are particularly low values for histidine, threonine, methionine and lysine; some other amino acids are sufficient for the majority of animals, but not all (threonine, tyrosine). Lime hydrolysis of alfalfa hay generates a product that is very rich in proline and asparagine, but these are not essential amino acids in the diet of domestic animals.







TABLE 24







Amino acid analysis of product and essential amino acids requirements


for various domestic animals (alfalfa hay)





















Dry




Amino
Cat-


Chick-

Prod-
Liquid
Raw


Acid
fish
Dogs
Cats
ens
Pigs
uct
(FAA)
Alfalfa


















ASN






17.17



GLN






0.00


ASP





7.52
5.62
14.44


GLU





11.40
11.29
11.85


SER





5.32
4.64
6.13


HIS
1.31
1.00
1.03
1.40
1.25
0.71
0.00
1.39


GLY





6.50
4.61
5.30


THR
1.75
2.64
2.43
3.50
2.50
2.53
1.96
4.95


ALA





4.55
3.87
5.63


ARG
3.75
2.82
4.17
5.50
0.00
6.36
8.00
5.58


VAL
2.63
2.18
2.07
4.15
2.67
9.00
4.07
5.61


CYS
2.00*
2.41*
3.67*
4.00*
1.92*
6.36
3.79
ND


MET
2.00*
2.41*
2.07
2.25
1.92*
0.95
0.48
1.01


TYR
4.38+
4.05+
2.93+
5.85+
3.75+
2.78
0.00
2.94


PHE
4.38+
4.05+
1.40
3.15
3.75+
5.53
0.95
5.59


ILE
2.28
2.05
1.73
3.65
2.50
5.54
2.34
4.40


LEU
3.06
3.27
4.17
5.25
2.50
10.77
2.83
10.06


LYS
4.47
3.50
4.00
5.75
3.58
1.49
0.58
5.77


TRP
0.44
0.91
0.83
1.05
0.75
ND
1.95
ND


PRO





12.70
25.85
9.35





*Cysteine + Methionine


+Tyrosine + Phenylalanine


FAA Free Amino Acids


All values are in g amino acid/100 g protein.






Differences between the two liquid samples (free vs. total amino acids) can be explained by acid degradation of some amino acids (especially tryptophan, asparagine and glutamine) in the total amino acid determination. Also, some protein in the centrifuged liquid may not have been hydrolyzed by the lime and may have been present as soluble polypeptides that were not detected by the HPLC analysis. The difference between the total amino acid in the liquid sample and the dry product is explained by the high concentration of suspended matter present in the liquid sample (centrifugation at 3500 rpm for 5 min). This suspended matter was not determined during the total amino acid measurement because the first step before HCL hydrolysis is centrifugation at 15000 rpm. The suspended matter forms an important part of the dry product and this explains the very different result for the amino acid composition.
The highest protein solubilization for alfalfa (68%) was achieved using 60 minutes, 0.075 g Ca(OH)2/g alfalfa, 100° C., and 60 g dry alfalfa/L. Protein solubilization increases with temperature; a higher initial concentration of alfalfa increases the conversion up to a limit between 60 and 80 g alfalfa/L.
Because of the high solubility of alfalfa components, protein solubilized was high and did not change dramatically for all the cases studied (43% to 68%). Lime loading has the least effect of the four variables studied, but some lime is required to prevent acids naturally present in the alfalfa from damaging the amino acids, and to obtain a higher ratio of free amino acids in the final product. Finally, the amino acid composition of the product compares poorly with the essential amino acid requirements for various monogastric domestic animals. The product is low in histidine (underestimated in the analysis), threonine, methionine, and lysine. It is especially rich in asparagine and proline, but these are not required in the animal diets. The protein product is most suited for ruminants.
Lime treatment increases the digestibility of the holocellulose fraction (Chang et al., 1998), providing added value to the residual solid from the thermo-chemical treatment. The use of both products as a ruminant feed ensures a more efficient digestion when compared to the initial material.
Example 3
Protein Solubilization in Soybean Hay
Soybeans are normally harvested for the generation of several food products. During the harvesting process, an unused waste product is generated in large quantities.
Additionally, some special weather conditions (e.g. long dry season, long rainy season) hamper soybean growth. A low crop yield directs the soybean harvest to the generation of animal feed (soybean hay), instead of the food industry.
Treatment of soybean hay will generate two separate products: a highly digestible soluble fraction and a delignified residual solid. The higher feed digestibility ensures that animal requirements will be satisfied with less feed.
Sun-cured soybean hay (i.e., leaves, stems, and beans of mowed soybean plants) was obtained from Terrabon Company; then it was ground using a Thomas-Wiley laboratory mill (Arthur H. Thomas Company, Philadelphia, P A) and sieved through a 40-mesh screen. The moisture content, the total nitrogen (estimate of the protein fraction), and the amino acid content were determined to characterize the starting material.
In Table 25, the composition of the soybeans in its different states is summarized.







TABLE 25







Composition of soybeans in its different states (McDonald et al., 1995)












Crude
Crude
Digestible




Fiber
Protein
Crude Protein
Starch and


Soybeans
(g/kg)
(g/kg)
(g/kg)
Sugar














Soybean meal
58
503
—
124


Soybean meal, full fat
48
415
—
 91


Hay, sun-cured
366
156
101
—









Soybean hay was 91.31% dry material and 8.69% moisture (Table 26). The TKN was 3.02% corresponding to a crude protein concentration in dry soybean hay of about 19% (Table 27). The remaining 81% corresponds to fiber, sugars, minerals, and others. The amino acid composition for raw alfalfa hay is given in Table 28.







TABLE 26







Moisture content of air-dried soybean hay













Solid
Dry Solid
Dry solid



Sample
(g)
(g)
(%)







1
5.1781
4.7297
91.34



2
5.5824
5.0967
91.30



3
5.4826
5.0048
91.29





Average
91.31

















TABLE 27







Protein and mineral content of air-dried soybean hay


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)





Raw Soy
3.0183
0.37
2.24
1.6477
0.3606
1399
34
280
13
53
















TABLE 28







Amino acid composition of air-dried soybean hay












Amino acid
Measured
Amino acid
Measured
















ASP
16.79
TYR
2.82



GLU
15.10
VAL
4.85



SER
5.65
MET
0.88



HIS
2.55
PHE
5.36



GLY
4.46
ILE
4.27



THR
4.23
LEU
9.32



ALA
4.82
LYS
5.93



CYS
ND
TRP
ND



ARG
7.75
PRO
5.21







ND: Not determined



Values in g AA/100 g total amino acids.






Experiment 1.
Repeatability of the Results
To determine the repeatability of the results on solubilizing protein in soybean hay, experiments were run at the same conditions: temperature, lime loading, and soybean hay concentration (100° C., 0.05 g lime/g soybean hay and 60 g dry soybean hay/L respectively). The experimental conditions studied and variables measured are summarized in Table 29.







TABLE 29







Experimental conditions and variables measured to determine


the repeatability of results in protein solubilization of soybean hay











Experiment
B
E
J
K














Mass of soybean hay (g)
55.9
55.9
55.9
55.9


Volume of water (mL)
850
850
850
850


Mass of lime (g)
2.8
2.8
2.8
2.8


Initial temperature (° C.)
93
93.5
105
98.1


pH final
8.6
8.9
8.6
8.9


Residual solid (g)
35.3
36.8
37
35.4


Dissolved solids in
2.5706
2.3927
2.7449
2.7116


100 mL (g)


Protein in 100 mL (g)
0.770
0.799
0.837
0.779









Table 30 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the same conditions of temperature, lime loading, and soybean hay concentration. On the basis of the average TKN for dry soybean hay (3.02%), protein hydrolysis conversions were estimated (Table 31).







TABLE 30







Total Kjeldhal nitrogen content in the centrifuged liquid


phase as a function of time for Experiment 1 (soybean hay)











Time (min)
B
E
J
K














0
0.0808
0.0741
0.0799
0.0831


5
0.0768
0.0837
0.0837
0.0876


15
0.0916
0.0876
0.0965
0.0996


30
0.1002
0.0939
0.1028
0.1078


45
0.1068
0.0977
0.1084
0.1203


60
0.1008
0.1009
0.1239
0.1222


150
0.1231
0.1277
0.1338
0.1246





TKN in g nitrogen/100 g liquid sample.













TABLE 31







Percentage conversion of the total TKN to soluble TKN for


Experiment 1 (soybean hay)














Time (min)
B
E
J
K
Average


















0
44.6
40.9
44.1
45.8
43.8



5
42.4
46.2
46.2
48.3
45.8



15
50.5
48.3
53.2
55.0
51.8



30
55.3
51.8
56.7
59.5
55.8



45
58.9
53.9
59.8
66.4
59.8



60
55.6
55.7
68.4
67.4
61.8



150
67.9
70.5
73.8
68.7
70.2










FIG. 21 presents the protein hydrolysis of soybean hay as a function of time for four different runs at the same experimental conditions. There is relatively small variability from one case to the other; the variance tends to increase at medium values and it is smaller at the extremes. From the time behavior, the values at 150 min are near the maximum conversion-because the rate of change is relatively small for all the cases.
Experiment 2.
Temperature Effect
To determine the effect of temperature on solubilizing protein in soybean hay, experiments were run at different temperatures keeping the lime loading and soybean hay concentration constant (0.05 g lime/g soybean hay and 60 g dry soybean hay/L, respectively). The experimental conditions studied and variables measured are summarized in Table 32.







TABLE 32







Experimental conditions and variables measured to determine


the effect of temperature in protein solubilization of soybean hay









Temperature (° C.)











75
100
115














Mass of soybean hay (g)
55.9
55.9
55.9


Volume of water (mL)
850
850
850


Mass of lime (g)
2.8
2.8
2.8


Initial temperature (° C.)
75.3
93
100.2


PH final
9.5
8.6
8


Residual solid (g)
36.2
35.3
34.6


Dissolved solids in 100 mL (g)
2.7593
2.5706
2.6568


Protein in 100 mL (g)
0.647
0.770
0.823









Table 33 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different temperatures. On the basis of the average TKN for dry soybean hay (3.02%), protein hydrolysis conversions were estimated (Table 34).







TABLE 33







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 2 (soybean hay)









Temperature












Time (min)
75° C.
100° C.*
115° C.
















0
0.0822
0.0795
0.0781



5
0.0869
0.0830
0.0856



15
0.0889
0.0938
0.093



30
0.0916
0.1012
0.1008



45
0.0969
0.1083
0.1094



60
0.0982
0.1120
0.1140



150
0.1035
0.1273
0.1315







*Average of the four experimental runs.



TKN in g nitrogen/100 g liquid sample.













TABLE 34







Percentage conversion of the total TKN to soluble


TKN for Experiment 2 (soybean hay)









Temperature












Time (min)
75° C.
100° C.*
115° C.
















0
45.4
43.8
43.1



5
47.9
45.8
47.2



15
49.0
51.8
51.3



30
50.5
55.8
55.6



45
53.5
59.8
60.4



60
54.2
61.8
62.9



150
57.1
70.2
72.6







*Average of the four experimental runs.






FIG. 22 presents the protein hydrolysis (percent conversion) as a function of time for the different temperatures studied. The conversion increases at higher temperatures. The conversion for 100° C. is similar to the one obtained at 115° C.; therefore, the lower temperature is favored because the amino acids should degrade less, the energy required is less, and the working pressure is lower.
An analysis of Table 32 shows again that pH decreased as protein solubilization increased because more lime reacts with amino acid products, and because the protein percentage of the product increases as conversion increases.
The conversions at 75° C. are statistically different from the ones at 100 and 115° C. In all the cases, the reaction rates tend to decrease at 150 min.
Experiment 3.
Lime Loading Effect
To determine the effect of lime loading on protein solubilization of soybean hay, experiments were run at different lime/soybean hay ratios keeping the temperature and soybean hay concentration constant (100° C. and 60 g dry soybean hay/L, respectively). The experimental conditions studied and variables measured are summarized in Table 35.







TABLE 35







Experimental conditions and variables measured to determine the lime


loading effect in protein solubilization of soybean hay









Lime loading (g lime/g soybean hay)











0
0.05
0.1














Mass of soybean hay (g)
55.9
55.9
55.9


Volume of water (mL)
850
850
850


Mass of lime (g)
0
2.8
5.6


Temperature (° C.)
100
100
100


Initial Temperature (° C.)
93.5
98.1
90.5


pH final
5.9
8.9
10.8


Residual solid (g)
36.1
35.4
34.4


Dissolved solids in 100 mL (g)
2.1803
2.7116
3.4937


Protein in 100 mL (g)
0.560
0.779
0.906









Table 36 shows the total nitrogen content in the centrifuged liquid samples as a function of time for different lime loadings. On the basis of the average TKN for dry soybean hay (3.02%), the protein hydrolysis conversions were estimated and are given in Table 37. The initial conversions are similar for all lime loadings because of the soluble components present in the soybean hay.







TABLE 36







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 3 (soybean hay)









Lime loading












Time (min)
0 (g/g)
0.05 (g/g)*
0.1 (g/g)
















0
0.0787
0.0795
0.0761



5
0.0850
0.0830
0.0811



15
0.0908
0.0938
0.1147



30
0.0895
0.1012
0.0965



45
0.0914
0.1083
0.1128



60
0.0888
0.1120
0.1178



150
0.0895
0.1273
0.1448







*Average of the four experimental runs.



TKN in g nitrogen/100 g liquid sample.













TABLE 37







Percentage conversion of the total TKN to soluble


TKN for Experiment 3 (soybean hay)









Lime loading












Time (min)
0 (g/g)
0.05 (g/g)*
0.1 (g/g)
















0
43.4
43.8
42.0



5
46.9
45.8
44.7



15
50.1
51.8
63.3



30
49.4
55.8
53.2



45
50.4
59.8
62.2



60
49.0
61.8
65.0



150
49.4
70.2
79.9







*Average of the four experimental runs.






FIG. 23 presents the protein solubilized (percentage conversion) as a function of time for the different lime loadings studied. The conversion increases as the lime loading increases, giving the maximum effect when changing from the no-lime experiment to the 0.05 g/g lime loading. “Equilibrium” is achieved in the no-lime case at 15 min and further treatment at 100° C. generates no additional protein solubilization. Hence, a minimum lime loading is required for efficient protein solubilization in soybean hay. The difference between 0.05 and 0.1 g/g of lime loading is statistically significant only for 150 min.
In the no-lime experiment, the final pH was 5.9. Likely, the pH went acidic because of acids (e.g., acetyl groups) released from the biomass and amino acids released from the proteins. Because no lime was used, the concentration of dissolved solids was lower. In all the other cases reported in Table 35, lime was a portion of the dissolved solids.
Experiment 4.
Soybean Hay Concentration Effect
To determine the effect of the initial soybean hay concentration on protein solubilization, experiments were run at different soybean hay concentrations keeping the temperature and lime loading constant (100° C. and 0.05 g lime/g soybean hay, respectively). The experimental conditions studied and variables measured are summarized in Table 38.







TABLE 38







Experimental conditions and variables measured for determining


the effect of initial soybean hay concentration in protein solubilization









Soybean hay concentration



(g dry soybean hay/L)











40
60
80














Mass of soybean hay (g)
37.8
53.4
75.6


Volume of water (mL)
850
800
850


Mass of lime (g)
2.9
4.0
5.7


Temperature (° C.)
75
75
75


Initial temperature (° C.)
78.2
73.2
82.1


pH final
10.7
11.3
11


Residual solid (g)
22.8
34.9
53.3


Dissolved solids in 100 mL (g)
2.0201
3.549
4.1349


Protein in 100 mL (g)
0.231
0.390
0.450









Table 39 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different soybean hay concentrations. On the basis of the average TKN for dry soybean hay (3.02%), the protein hydrolysis conversions were estimated and are given in Table 40.







TABLE 39







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 4 (soybean hay)









Soybean hay concentration












Time (min)
40 g/L
60 g/L
80 g/L
















0
0.0531
0.0741
0.1065



5
0.0503
0.0837
0.1215



15
0.0592
0.0876
0.1264



30
0.0639
0.0939
0.1399



45
0.0681
0.0977
0.1514



60
0.0701
0.1009
0.1472



150
0.1028
0.1277
0.1221







TKN in g nitrogen/100 g liquid sample.













TABLE 40







Percentage conversion of the total TKN to soluble


TKN for Experiment 4 (soybean hay)









Soybean hay concentration












Time (min)
40 g/L
60 g/L
80 g/L
















0
44.0
43.8
44.1



5
41.7
45.8
50.3



15
49.1
51.8
52.3



30
53.0
55.8
57.9



45
56.5
59.8
62.7



60
58.1
61.8
60.9



150
85.2
70.2
50.5










FIG. 24 presents the protein solubilization (percentage conversion) as a function of time for the different soybean hay concentrations studied. It shows that protein solubilization does not vary with soybean hay concentration for times smaller than 60 min. The values at 150 min probably have some sampling problems because the results are not comparable with previous values. From Table 38, the dissolved solids and the protein present in the final product increase as the concentration of soybean hay increases.
A comparison between the compositions of the raw material and the residual solid gives information on the effectiveness of lime-treating soybean hay for protein solubilization. The composition for both materials is shown in Table 41. These results were obtained for 100° C., 0.05 g lime/g soybean hay and 60 g soybean hay/L.







TABLE 41







Comparison of protein and minerals content present in the raw soybean


hay with the residual solid and the centrifuged liquid after lime treatment


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















Raw Soy
3.0183
0.37
2.24
1.6477
0.3606
1399
34
280
13
53


Residual solid
1.9824
0.33
0.78
3.1171
0.1845
1326
19
158
9
35


Centrifuged
0.1176
0.0104
0.155
0.2114
0.0146
104
2
10
0
2


liquid





*For 150 min.






Table 41 shows that the calcium concentration of the residual solid is greater than in the raw soybean hay. This value increases due to the lime added for the treatment, which is not completely soluble in water. The values for other minerals decrease during the lime treatment due to the high solubility of these salts. The nitrogen present in the residual solid is 33% smaller than the value obtained for the raw material before lime treatment.
The centrifuged liquid has a very high concentration of calcium, due to lime, and this implies that the calcium concentration in the final product (after water evaporation of centrifuged liquid) will be higher than the nitrogen content. The ratio of protein to calcium in the final product is:

ratio=(0.1176×6.25)/0.2114=3.48 g protein/g Ca.

The fraction of soybean hay that was solubilized is calculated as follows:

soluble fraction=1−{26.2 g residual solids−[(15.6 g dissolved solids/572 mL liquid)*200 mL moisture]}/55.9 g initial soybean hay=0.450 g solubilized/g of soybean hay.

This calculation corrects for the dissolved solids contained in the 200 mL of liquid. The solids were not washed, so the retained liquid includes dissolved solids. This value (0.450 g solubilized/g soybean hay) is reported in Table 42.







TABLE 42





Variables measured for 100° C., 0.05 g lime/g


soybean hay, and 60 g soybean hay/L


















Mass of soybean hay (g)
55.9
pH final
9.7


Volume of water (mL)
850
Residual solid (g)
36.2


Mass of lime (g)
2.8
Dissolved solids in 572 mL (g)
15.6


Temperature (° C.)
100
Soluble fraction of soybean hay
0.45









Experiment 5.
Amino Acid Analysis
Soybean hay was treated with lime at 150 mm and 24 h with the recommended conditions: 100° C., 0.05 g lime/g soybean hay, and 60 g soybean hay/L. The amino acid analysis was performed in three different ways:

    
    
        1) Centrifuged liquid product-Free amino acid analysis. The analysis was made without extra HCL hydrolysis of the sample. No amino acids were destroyed by the analytical procedure, but soluble polypeptides might be missed in the analysis.
        2) Centrifuged liquid product-Total amino acid analysis. The analysis was made with 24-h HCL hydrolysis of the sample. Some amino acids were destroyed by the analytical procedure or converted to other amino acids; soluble polypeptides are measured in the analysis.
        3) Dry product after evaporating water from the centrifuged liquid. Because this sample was solid, HCL hydrolysis was required. Some amino acids (asparagine, glutamine, and tryptophan) were destroyed by the acid and could not be measured.
    
    


Table 43 and Table 44 show the free amino acids and the total amino acids concentration for lime treated soybean hay at 150 min and 24 h, respectively. Table 45 shows the protein and mineral content for both samples.







TABLE 43







Free and total amino acid concentration for the centrifuged


liquid product of lime-hydrolyzed soybean hay at 150 min










Non hydrolyzed-free




amino acids
Hydrolyzed-total amino acids











Amino
Concentration
Percentage
Concentration
Percentage


acid
(mg/L)
(%)
(mg/L)
(%)














ASN
213.48
30.64
0.00
0.00


GLN
0.00
0.00
0.00
0.00


ASP
69.49
9.97
447.76
33.01


GLU
46.46
6.67
172.72
12.73


SER
9.12
1.31
52.72
3.89


HIS
14.51
2.08
35.29
2.60


GLY
61.58
8.84
106.68
7.87


THR
6.36
0.91
37.01
2.73


ALA
20.63
2.96
58.07
4.28


ARG
97.44
13.98
142.70
10.52


TYR
0.00
0.00
16.78
1.24


CYS
36.45
5.23
0.00
0.00


VAL
20.71
2.97
48.20
3.55


MET
0.00
0.00
0.00
0.00


PHE
25.63
3.68
55.38
4.08


ILE
10.35
1.48
34.89
2.57


LEU
13.21
1.90
54.62
4.03


LYS
0.00
0.00
37.77
2.78


TRP
25.86
3.71
0.00
0.00


PRO
25.58
3.67
55.72
4.11


Total
696.85
100
1356.33
100
















TABLE 44







Free and total amino acid concentration for the centrifuged


liquid product of lime-hydrolyzed soybean hay at 24 h










Non hydrolyzed-free




amino acids
Hydrolyzed-total amino acids











Amino
Concentration
Percentage
Concentration
Percentage


acid
(mg/L)
(%)
(mg/L)
(%)














ASN
98.37
17.04
0.00
0.00


GLN
0.00
0.00
0.00
0.00


ASP
82.54
14.30
336.84
25.65


GLU
45.62
7.90
196.13
14.93


SER
6.44
1.12
52.93
4.03


HIS
0.00
0.00
25.71
1.96


GLY
97.90
16.96
150.13
11.43


THR
0.00
0.00
33.85
2.58


ALA
26.50
4.59
69.22
5.27


ARG
81.84
14.18
122.09
9.30


TYR
0.00
0.00
20.91
1.59


CYS
34.26
5.94
0.00
0.00


VAL
19.19
3.33
50.05
3.81


MET
0.00
0.00
0.00
0.00


PHE
21.72
3.76
54.20
4.13


ILE
10.79
1.87
37.79
2.88


LEU
7.83
1.36
60.64
4.62


LYS
0.00
0.00
35.50
2.70


TRP
23.27
4.03
0.00
0.00


PRO
20.88
3.62
67.49
5.14


Total
577.16
100
1313.48
100
















TABLE 45







Comparison of protein and minerals content present in the


centrifuged liquid of lime-treatment of soybean hay


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)





















150
min
0.1176
0.0104
0.155
0.2114
0.0146
104
2
10
0
2


24
h
0.1562
0.0146
0.149
0.2716
0.0186
104
2
16
0
2









For both cases, the total amino acid concentration is approximately twice the free amino acid concentration. This shows that 50% of the amino acids are present in the form of small peptides.
For all the experiments, the centrifuged liquid contained a very high concentration of suspended particulate matter that might be measured in the Kjeldhal determination but not in the amino acid analysis. This explains the difference between the amino acid determination and the estimated protein concentration from Kjeldhal analysis (1.36 vs. 7.35 and 1.31 vs. 9.76 g protein/L).
A comparison of Tables 43-35 show that although the nitrogen concentration increases from 150 min to 24 h, the total amino concentration remains relatively constant, so, there is no need for a long treatment in the hydrolysis of soybean hay.
Finally, the amino acid composition of the protein product is compared to the essential amino acid needs of various domestic animals.
Table 46 shows that the amino acid product from the hydrolysis of soybean hay is not well balanced with respect to the requirements of different monogastric domestic animals. There are especially low values for histidine, threonine, methionine, and lysine; some other amino acids (tyrosine, valine) are sufficient for the majority of the animals, but not all. The lime hydrolysis of soybean hay generates a product that is very rich in asparagine, which is not essential in the diet of domestic animals. The protein product is best suited for ruminants.







TABLE 46







Amino acid analysis of product and essential amino acids requirements


for various domestic animals (soybean hay)





















Dry

Raw


Amino Acid
Catfish
Dogs
Cats
Chickens
Pigs
Product
Liquid (FAA)
material


















ASN






30.64



GLN






0.00


ASP





6.68
9.97
16.79


GLU





9.56
6.67
15.10


SER





7.11
1.31
7.84


HIS
1.31
1.00
1.03
1.40
1.25
0.00
2.08
2.55


GLY





10.69
8.84
4.46


THR
1.75
2.64
2.43
3.50
2.50
1.80
0.91
4.23


ALA





5.05
2.96
4.82


ARG
3.75
2.82
4.17
5.50
0.00
6.19
13.98
7.75


VAL
2.63
2.18
2.07
4.15
2.67
7.08
2.97
4.85


CYS
2.00*
2.41*
3.67*
4.00*
1.92*
9.22
5.23
ND


MET
2.00*
2.41*
2.07
2.25
1.92*
0.87
0.00
0.88


TYR
4.38+
4.05+
2.93+
5.85+
3.75+
2.71
0.00
2.82


PHE
4.38+
4.05+
1.40
3.15
3.75+
5.26
3.68
5.90


ILE
2.28
2.05
1.73
3.65
2.50
5.15
1.48
4.27


LEU
3.06
3.27
4.17
5.25
2.50
9.81
1.90
9.32


LYS
4.47
3.50
4.00
5.75
3.58
1.10
0.00
5.93


TRP
0.44
0.91
0.83
1.05
0.75
ND
3.71
ND


PRO





11.70
3.67
5.21





*Cysteine + Methionine


+Tyrosine + Phenylalanine


FAA Free Amino Acids


All values are in g amino acid/100 g protein.






Differences between the two liquid samples (free vs. total amino acids—Table 43 and Table 45) can be explained by acid degradation of some amino acids (especially tryptophan, asparagine, and glutamine) in the total amino acid determination. Also, some protein in the centrifuged liquid may not have been hydrolyzed by the lime and may have been present as soluble polypeptides that were not detected by the HPLC analysis. The difference between the total amino acid in the liquid sample and the dry product is explained by the high concentration of suspended matter present in the liquid sample (centrifugation at 3500 rpm for 5 min). This suspended matter was not determined during the total amino acid measurement because the first step before HCL hydrolysis is centrifugation at 15000 rpm. The suspended matter forms an important part of the dry product and this explains the very different result for the amino acid composition.
The highest protein solubilization (85%) was achieved using 0.05 g Ca(OH)2/g soybean hay, 150 minutes, 100° C., and 40 g dry soybean hay/L. The effect of the variables studied in this experiments can be summarized as:
Protein solubilization increases with temperature, with 100° C. giving the same results as 115° C. The recommended temperature is 100° C. because the energy requirements are smaller and no pressure vessel is required. The initial concentration of soybean hay has no important effect in the protein solubilization at times less than 60 min. A minimum lime loading (at least 0.05 g Ca(OH)2/g soybean hay) is required to efficiently solubilize protein. For all cases, protein solubilization increases with time and the maximum values obtained are for 150 min. Soybean hay concentration has the least significant effect of the four variables studied.
A comparison of the amino acid analysis for the hydrolysis product and the essential amino acids requirements for various monogastric domestic animals shows it is not a well-balanced product. It has a high concentration of asparagine, a nonessential amino acid.
As in the alfalfa hay case, the protein product is most suited for ruminants. The lime treatment increases the digestibility of the holocellulose fraction (Chang et al., 1998), providing an added value to the residual solid from the thermo-chemical treatment. The used of both products as a ruminant feed ensures a more efficient digestion when compared to the initial material.
Example 4
Protein Solubilization in Chicken Offal
Chicken offal was obtained from the Texas A&M Poultry Science Department. Although in general, offal may contain bones, heads, beaks, and feet, in this case, it had only internal organs (e.g., heart, lungs, intestine, liver). The offal was blended for 10 min in an industrial blender, collected in plastic bottles, and finally frozen at −4° C. for later use. Samples of this blended material were used to obtain the moisture content, the total nitrogen (estimate of the protein fraction), the ash (mineral fraction), and the amino acid content to characterize the starting material.
Equation 1 defines the conversion of the centrifuged sample based on the initial total Kjeldhal nitrogen (TKN) of offal:




  
    
      
        
          Conv
          1
        
        =
        
          
            
              
                V
                water
              
              ×
              
                TKN
                
                  centrifuged
                  ⁢
                  
                    
                  
                  ⁢
                  liquid
                
              
            
            
              
                m
                
                  dry
                  ⁢
                  
                    
                  
                  ⁢
                  offal
                
              
              ×
              
                TKN
                
                  dry
                  ⁢
                  
                    
                  
                  ⁢
                  offal
                
              
            
          
          .
        
      
    
    
      
        (
        1
        )
      
    
  




Equation 2 defines the conversion of the non-centrifuged sample based on the initial total Kjeldhal nitrogen (TKN) of offal:




  
    
      
        
          Conv
          2
        
        =
        
          
            
              
                V
                water
              
              ×
              
                TKN
                
                  non
                  -
                  
                    centrifuged
                    ⁢
                    
                      
                    
                    ⁢
                    liquid
                  
                
              
            
            
              
                m
                
                  dry
                  ⁢
                  
                    
                  
                  ⁢
                  offal
                
              
              ×
              
                TKN
                
                  dry
                  ⁢
                  
                    
                  
                  ⁢
                  offal
                
              
            
          
          .
        
      
    
    
      
        (
        2
        )
      
    
  




Equation 3 estimates the fractional loss TKN of the initial offal nitrogen, using a mass balance:




  
    
      
        
          L
          TKN
        
        =
        
          1
          -
          
            
              
                
                  V
                  water
                
                ×
                
                  TKN
                  
                    non
                    -
                    
                      centrifuged
                      ⁢
                      
                        
                      
                      ⁢
                      liquid
                    
                  
                
              
              
                
                  m
                  
                    dry
                    ⁢
                    
                      
                    
                    ⁢
                    offal
                  
                
                ×
                
                  TKN
                  
                    dry
                    ⁢
                    
                      
                    
                    ⁢
                    offal
                  
                
              
            
            .
          
        
      
    
    
      
        (
        3
        )
      
    
  




The raw offal was 33.3% dry material and 66.7% moisture (see Table 47). The crude protein concentration of the dry offal was about 45% and the ash content was about 1%; the remaining 54% was fiber and fat.







TABLE 47







Water content of the raw offal













Offal
Dry matter
% Dry



Crucible
(g)
(g)
Weight







J
32.2197
10.6402
33.024



A
30.8807
10.4548
33.855



4
28.6961
9.512
33.147





Average
33.342







Dry matter (oven at 105° C.).






Experiment 1.
Effect of Process Variables
Experiment 1 included eight runs labeled A through H. Runs A, B, and C were tested at 100° C., with 20 g dry offal/L and 0.1 g Ca(OH)2/g dry offal. These conditions were obtained from the optimum results of a previous experiment that studied the same type of reaction for chicken feathers (Chang and Holtzapple, 1999). The remaining runs (D through H) were performed at different operating conditions, as shown in Table 48.







TABLE 48







Experimental conditions used in Experiment 1 (chicken offal)
















Mass of
Mass of wet
Volume of
Ca(OH)2
Conc. of




Temperature
Ca(OH)2
Offal
water
Loading
dry Offal


Run
(° C.)
(g)
(g)
(mL)
(g/g dry offal)
(g/L)
Final pH

















A
100
1.70
51.5
850
0.099
20.20
9.50


B
100
1.70
51.2
850
0.100
20.08
9.65


C
100
1.70
51.5
850
0.099
20.20
9.50


D
100
3.40
102.3
850
0.100
40.13
9.55


E
100
5.10
153.3
850
0.100
60.13
9.50


F
100
2.55
102.5
850
0.075
40.21
8.90


G
100
1.70
102.4
850
0.050
40.17
9.10


H
75
3.40
102.4
850
0.100
40.17
10.10









Table 49 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the eight runs. On the basis of the average TKN for dry offal (7.132%), the protein hydrolysis conversions were estimated and are given in Table 50. The conversions in Table 50 are presented graphically in FIGS. 25-28 V.4.







TABLE 49







Total Kjeldhal nitrogen content in centrifuged liquid phase as a function


of time for Experiment 1 (chicken offal)









Experiment















Time (min)
A
B
C
D
E
F
G
H


















5
0.0698
0.0520
0.0635
0.1332
0.2112
0.1438
0.0862
0.1191


10
0.0721
0.0543
0.0658
0.1354
0.2112
0.1461
0.0851
0.1191


15
0.0721
0.0543
0.0647
0.1366
0.2134
0.1473
0.0851
0.1213


25
0.0721
0.0554
0.0658
0.1388
0.2156
0.1495
0.0874
0.1179


35
0.0721
0.0566
0.0647
0.1388
0.2145
0.1517
0.0874
0.1191


45
0.0721
0.0554
0.0635
0.1388
0.2168
0.1495
0.0874
0.1179


60
0.0721
0.0600
0.0658
0.1399
0.2156
—
—
—


90
0.0721
0.0600
0.0669
0.1445
0.2156
—
—
—


120
0.0721
0.0589
0.0669
0.1433
0.2168
0.1507
0.0918
0.1202


180
0.0765
0.0623
0.0681
0.1433
0.2179
—
—
—





TKN in g nitrogen/100 g liquid sample.













TABLE 50







Fractional conversion of the total TKN to soluble TKN


for Experiment 1 (chicken offal - Equation 1)









Experiment















Time (min)
A
B
C
D
E
F
G
H


















5
0.467
0.350
0.425
0.466
0.511
0.502
0.301
0.416


10
0.482
0.365
0.440
0.473
0.511
0.510
0.297
0.416


15
0.482
0.365
0.433
0.478
0.516
0.514
0.297
0.424


25
0.482
0.373
0.440
0.485
0.522
0.522
0.305
0.412


35
0.482
0.381
0.433
0.485
0.519
0.529
0.305
0.416


45
0.482
0.373
0.425
0.485
0.525
0.522
0.305
0.412


60
0.482
0.404
0.440
0.489
0.522
—
—
—


90
0.482
0.404
0.447
0.505
0.522
—
—
—


120
0.482
0.396
0.447
0.501
0.525
0.526
0.321
0.420


180
0.512
0.419
0.456
0.501
0.527
—
—
—









FIG. 25-28 show that at these conditions, the conversion of nitrogen in the solid phase to the liquid phase was not efficient (between 45 and 55%). This implies that much of the protein of the solid phase does not react with the hydroxide or that the amino acids formed precipitate back to the solid phase. Another consideration is the presence of fats in the raw material that consume hydroxide and therefore slows the protein hydrolysis.
FIG. 25-28 show that the reaction occurs during the first 10 or 15 min of contact time and then the conversion (concentration) stays constant.
FIG. 25 shows that the results from different runs employing the same experimental conditions give comparable conversions. FIG. 26 shows that the conversions are similar for different initial concentrations of raw material. This means that the amino acid concentration in the liquid phase will be higher for a higher starting concentration of offal.
FIG. 27 shows that low lime loadings have low conversions; therefore, the reaction needs a minimum loading. Because similar results are obtained for 0.075 and 0.1 lime loading, the minimum 0.075 g Ca(OH)2/g dry offal will be used. FIG. 28 shows that at 75° C., the reaction is almost as fast as it is at 100° C. The lower temperature is favored because the amino acids should degrade less.
Experiment 2.
Process Optimization
In Experiment 2, the objective was to find conditions in which the conversion is higher (more efficient). Experiment 2 included a total of eight runs labeled I through P. Because the reaction is fast and the conversion is constant after 15 min, only one sample is needed to obtain a representative condition of the reaction. Table 51 shows the experimental conditions and the TKN concentration in liquid samples.







TABLE 51







Experimental conditions and results for Experiment 2


(chicken offal - two samples for each run)
















Conc. of
Conc. of







Temperature
Ca(OH)2
dry Offal
Final
Time


Run
(° C.)
(g/g dry offal)
(g/L)
pH
Sample
TKN
TKN


















I
50
0.100
40
8.35
1.5
h
0.2067
0.2067


J
100
0.075
40
8.45
30
min
0.169
0.2209(a)


K
100
0.075
40
8.45
2
h
0.1722
0.2296(a)


L
75
0.075
40
—
30
min
0.2046
0.234(a)


M
75
0.075
40

2
h
0.2231
0.2318(a)


N
100
0.400
40
12.05
1
h
0.1116
0.1094


O
100
0.300
40
12.0
1-2
h
0.1203
0.1289


P
75
0.300
40
12.0
1-2
h
0.143
0.1463





(a)Non-centrifuged liquid sample.


TKN in g nitrogen/100 g liquid sample.






Table 52 shows that for Runs I through M, the conversion ranges from 63% to 84% using Equation 1 (i.e., liquid TKN per TKN added in solids). For runs J through M, the conversion ranges from 83% to 87% using Equation 2 (i.e., liquid TKN in non-centrifuged sample per TKN added in solids). Equation 3, for runs J to M, shows a loss of 13% of the initial offal nitrogen at 75° C. and a loss of 15% of the initial offal nitrogen at 100° C. It is unclear where the lost nitrogen goes. Perhaps it is lost into the gas phase, or perhaps it attaches to metal surfaces in the reactor. Table 51 and Table 52 show that for the runs with the highest conversions, the final pHs are lower than all those obtained for Experiment 1 and for the other runs in Experiment 2. From Experiment 2, one may recommend a temperature of 75° C., with a lime loading of 0.075 g Ca(OH)2/g dry offal.







TABLE 52







Fractional conversion of the total TKN to soluble


TKN for Experiment 2 (chicken offal)













Conversion
Conversion
Fractional



Run
Sample 1
Sample 2
loss of TKN







1
0.781(1)
0.781(1)




J
0.634(1)
0.829(2)
0.171(3)



K
0.646(1)
0.861(2)
0.139(3)



L
0.768(1)
0.879(2)
0.121(3)



M
0.838(1)
0.870(2)
0.130(3)



N
0.436(1)
0.411(1)



O
0.452(1)
0.484(1)



P
0.536(1)
0.548(1)







(1)Conversion calculated using Equation 1.



(2)Conversion calculated using Equation 2.



(3)Lost nitrogen calculated using Equation 3.






Experiment 3.
Analysis of Final Product
FIG. 29 shows the amino acid spectrum for two centrifuged liquid samples obtained under conditions of Experiment 2 (lime loading 0.075 g Ca(OH)2/g dry offal, temperature 75° C., offal concentration 40 g dry offal/L, and time 1 h). First, the amino acid composition in the raw centrifuged liquid sample without further treatment was determined by HPLC analysis. Second, the centrifuged liquid sample was treated with 6-N HCL for 1 h, which hydrolyzed protein to its corresponding amino acids. By comparing both results, one may conclude that lime hydrolyzes the chicken offal into individual amino acids; the results of the two cases are essentially identical.
FIG. 30 compares the amino acid spectrum for the raw offal and for the solid residue that remains after lime treatment. To do this, the residual solids were dried at 105° C. for 24 h, a sample was taken for protein measurement. Because the water content of this solid residue was about 80%, the measured protein came from both the liquid and solid phases. The amino acid content in the residual solids is much less than in the raw offal because amino acids have dissolved into the liquid phase.
Using mass balances and the data shown in Figure V.6, the amount of each amino acid “extracted” from the raw material ranges from 50% to 75%. However, this includes the protein in the liquid adhering to the solids. If one subtracts the protein dissolved in the adhered liquid, the extraction for each amino acid ranges from 52% to 76% of the crude protein, which is similar to the results obtained in Experiment 2.
Another important issue is to determine the degradation of individual amino acids at the reactor operating conditions. To determine this, one needs to obtain the amino acid concentration at two different times. FIG. 31 shows that the amino acids present in the centrifuged liquid phase at 30 min are nearly identical to those at 2 h; implying that the amino acids are stable at the operating conditions. FIG. 32 shows that with a different starting concentration of offal; again, the amino acids have the same concentration at 30 min and 2 h.
FIG. 33 compares the results of three different initial offal concentrations, for the same time, temperature, and lime loading. These results show that the amino acid concentration in the centrifuged liquid phase is higher for a higher initial concentration of raw material, as expected.
FIG. 34 examines the amino acid concentration as a function of time for the first 10 min of reaction. The concentration stabilizes for all amino acids after 10 min, and the 30-min values are also comparable. This implies that the reaction occurs during the first 10 to 30 min of contact, as concluded in Experiment 1.
From the experiments performed using HPLC and Kjeldhal methods, the nitrogen content was comparable in both the cases (see Table 53). These results imply that the main contribution to the total nitrogen content is from the amino acids (i.e., the protein content of the chicken offal).







TABLE 53







Comparison of results for nitrogen content


(g nitrogen/100 g liquid sample) with HPLC and


Kjeldhal methods for experiments in FIG. V.10












2 min
3 min
5 min
10 min

















HPLC
0.065
0.072
0.211
0.216



Kjeldhal
0.11
0.11
0.18
0.17










Table 54 compares the various requirements for essential amino acids to the needs of various domestic animals, which are presented in Table 55. Table 56 indicates the compositions of various common animal fees and may also be compared to Table 54.







TABLE 54







Comparison of the amino acid present in the liquid phase of two


experiments: (a) at 75°, 0.075 g Ca(OH)2/g dry offal,


60 g dry offal/L, and 30 min; and (b) at 50° C., 0.100 g


Ca(OH)2/g dry offal, 40 g dry offal/L, and 90 min with the


dietary requirement of different animals




















Solu-
Solu-








bilized
bilized


Amino





Offal
Offal


Acid
Catfish
Dogs
Cats
Chickens
Pigs
(a)
(b)

















ASN





2.14
0.82


ASP





3.62
6.36


GLU





10.56
8.70


SER





4.54
7.21


HIS
1.31
1.00
1.03
1.40
1.25
2.92
2.23


GLY





4.89
5.35


THR
1.75
2.64
2.43
3.50
2.50
5.74
6.47


ALA





8.47
6.66


ARG
3.75
2.82
4.17
5.50
0.00
7.95
5.22


VAL
2.63
2.18
2.07
4.15
2.67
7.53
6.60


CYS
2.00*
2.41*
3.67*
4.00*
1.92*
0.7
ND


MET
2.00*
2.41*
2.07
2.25
1.92*
3.83
4.23


TYR
4.38+
4.05+
2.93+
5.85+
3.75+
1.68
4.36


PHE
4.38+
4.05+
1.40
3.15
3.75+
5.42
4.65


ILE
2.28
2.05
1.73
3.65
2.50
6.36
5.19


LEU
3.06
3.27
4.17
5.25
2.50
10.91
9.37


LYS
4.47
3.50
4.00
5.75
3.58
3.27
7.42


TRP
0.44
0.91
0.83
1.05
0.75
2.26
ND


PRO





6.11
6.98





*Cysteine + Methionine


+Tyrosine + Phenylalanine


ND Not determined


Values expressed as g individual amino acid per 100 g total amino acids.













TABLE 55







Nutritional requirement for domestic animals during growth phase


(Pond et al., 1995)
















Chicken




Catfish
Dogs
Cats
Broiler
Pigs















Crude protein (%)
32.0
22.0
30.0
20.0
12.0


Arginine (%)
1.20
0.62
1.25
1.10
0.00


Methionine (%)
0.64*
0.53*
0.62
0.45
0.23*


Cysteine (%)
0.64*
0.53*
1.10*
0.80*
0.23*


Histidine (%)
0.42
0.22
0.31
0.28
0.15


Isoleucine (%)
0.73
0.45
0.52
0.73
0.30


Leucine (%)
0.98
0.72
1.25
1.05
0.30


Lysine (%)
1.43
0.77
1.20
1.15
0.43


Tyrosine (%)
1.40**
0.89**
0.88**
1.17**
0.45**


Phenylalanine (%)
1.40**
0.89**
0.42
0.63
0.45**


Threonine (%)
0.56
0.58
0.73
0.70
0.30


Tryptophan (%)
0.14
0.20
0.25
0.21
0.09


Valine (%)
0.84
0.48
0.62
0.83
0.32





Notes:


1) *Cysteine + Methionine


2) **Tyrosine + Phenylalanine


3) All values are expressed as percentage of the total diet (g/100 g feed).













TABLE 56







Composition of different feed used in the diet of domestic animals (Pond et al., 1995)






















Meat










and



Blood
Fish
Soybean
Gluten
Corn

bone
Feather



meal
meal**
meal
meal
meal
Milo
meal
meal


















Dry matter (%)
91.0
92.0
89
91.0
93.0
89.0
94
91.0


Crude fiber (%)
1.0
0.9
6.0
4.0
12.0
2.0
2.4
4.7


Crude protein (%)
79.9
61.2
45.8
42.9
18.0
11.0
50.9
85.4


Digestibility (%)*
62.3
56.4
41.7
35.7
14.8
7.8
45.0
60.2


Arginine (%)
3.50
3.74
3.20
1.40
1.20
0.36
3.05
5.33


Cysteine (%)
1.40
0.58
0.67
0.60
0.32
0.18
0.46
3.21


Glycine (%)
3.40
—
2.10
1.50
—
0.40
—
—


Histidine (%)
4.20
1.44
1.10
1.00
—
0.27
0.96
0.47


Isoleucine (%)
1.00
2.85
2.50
2.30
—
0.53
1.47
3.51


Leucine (%)
10.30
4.48
3.40
7.60
1.70
1.42
3.02
0.42


Lysine (%)
6.90
4.74
2.90
0.80
0.90
0.27
2.89
1.67


Methionine (%)
0.90
1.75
0.60
1.00
0.35
0.09
0.08
0.54


Phenylalanine (%)
6.10
2.46
2.20
2.90
0.80
0.45
1.65
3.59


Threonine (%)
3.70
2.51
1.70
1.40
0.90
0.27
1.60
3.63


Tryptophan (%)
1.10
0.65
0.60
0.20
0.30
0.09
0.28
0.52


Tyrosine (%)
1.80
1.93
1.40
1.00
1.50
0.36
0.79
2.35


Valine (%)
6.50
3.19
2.40
2.20
1.30
0.53
2.14
5.85





Notes:


1) *As-fed basis for ruminants.


2) **There are three types of fish meal: anchovy, menhaden and herring. The values given are for menhaden.


3) The values of the amino acids are in percentage as-fed basis (g amino acid/100 g feed).






The tabulated results imply that the solubilized protein meets, or exceeds, the essential amino acids requirements of the animals during their growth phase for the run at 50° C. On the other hand, at 75° C. (optimum conversion conditions), the values for tyrosine and lysine are lower than the requirements.
Chicken offal, containing 15% protein (wet basis) or 45% protein (dry basis), can be used to obtain an amino acid-rich product by treating with Ca(OH)2 at temperatures less than 100° C. A simple non-pressurizing vessel can be used for the above process due to the low temperature requirements.
For all conditions of temperature, lime loading, and offal concentration that were studied, no significant change in the conversion occurred after 30 minutes of reaction.
The optimal conditions to maximize the protein conversion (up to 80%) are 0.075 g Ca(OH)2/g dry offal processed at 75° C. for at least 15 min. Initial offal concentration had no significant effect either on the conversion or the amino acid spectrum of the product.
However, a high offal concentration is recommended to obtain a highly concentrated product, thus reducing the energy requirements for concentrating the final product.
Little amino acid degradation was observed for all experiments performed below 100° C. and up to 2 hours. Thus, little degradation should occur by evaporating the liquid product at temperatures around 100° C.
At 50° C., the spectrum of essential amino acids obtained meets or exceeds the requirements for many domestic animals during their growth period. Thus, the amino acid-rich solid product obtained by lime treating chicken offal could serve as a protein supplement for these animals. The product obtained at 75° C. has a smaller amount of lysine and tyrosine than required and therefore will not be as efficient.
Example 5
Protein Solubilization in Chicken Offal and Feathers
Disposal of animal organs by the slaughter industry is an important environmental issue. The poultry industry generates a large amount of wastes (offal, feathers, and blood) centralized in the slaughterhouses in volumes that are large enough to develop techniques for processing these wastes. If the wastes are collected separately, they can be processed into blood meal (heat-dried blood used as a feed supplement), hydrolyzed feather meal, poultry meal, and fat.
Five percent of the body weight of poultry is feathers. Because of their high protein content (89.7% of dry weight, Table 57), feathers are a potential protein source for food, but complete destruction of the rigid keratin structure is necessary (Dalev, 1994).







TABLE 57







Composition of poultry offal and chicken feathers


(Wisman et al., 1957, and Dalev, 1994)















Feathers



% total weight
Fresh offal
Dry matter
(dry matter)
















Moisture
69.5
—
—



Crude protein
17.2
56.5
89.7



Ether extract (fat)
8.0
26.2
1.4



Crude fiber
0.1
0.4
ND



Ash
3.7
12.1
6.3



Nitrogen free extract
1.5
4.8
ND



Calcium (Ca)
0.5
1.7
0.35



Phosphorus (P)
0.6
2.0
0.13



Sodium (Na)
ND
—
0.4



Potassium (K)
ND
—
0.9










Poultry offal contains much more histidine, isoleucine, lysine, and methionine than chicken feathers (characteristics of chicken offal and feathers are shown in Table 57s to 59.). Hence, poultry offal and feathers meal together would have a better balance of amino acids (E I Boushy and Van der Poel, 1994). A feathers/offal process may accommodate the fact that feathers are harder to decompose or hydrolyze than offal.







TABLE 58







Amount of viable microorganisms in poultry offal (Acker et al., 1959)











Unwashed
Washed
Agar used














Total aerobes
280000
90000
Trypticase soy


Total anaerobes
98000
28000
Linden thioglycollate


Spore forming anaerobes
4500
2000
Linden thioglycollate


(Clostridium botulinum)


Coliforms (Salmonella)
20000
9000
Violet red bile


Lactobacilli
270000
97000
Tomato juice


Yeasts
28000
26000
Littman oxgall


Cottony molds
<100
<100
Littman oxgall





Count/g wet weight.













TABLE 59







Composition of poultry offal (Acker et al., 1959)











Unwashed
Washed
Units














Crude protein
20.5
17.7
g/100 g wet matter


Digestible protein
91.2
91.5
g/100 g protein


Ether extract
8.4
7.6
g/100 g wet matter


Crude fiber
1.1
1.0
g/100 g wet matter


Moisture
68.5
72.1
g/100 g wet matter


Ash
4.0
4.3
g/100 g wet matter


Loss on ignition
27.5
23.5
g/100 g dry matter


Calcium
1.4
1.8
g/100 g wet matter


Phosphorus
1.1
1.3
g/100 g wet matter


Riboflavin
3.8
3.1
mg/100 g dry matter


Niacin
4.8
6.3
mg/100 g dry matter


Ca pantothenate
2.3
1.1
mg/100 g dry matter


Pyrodoxine
0.11
0.09
mg/100 g dry matter


B12
52.6
9.5
μg/100 g dry matter


Vitamin A
806.8
1163.9
USP units/100 g dry matter


Carotene
356.2
656.8
Int'l units/100 g dry matter


Total Vit. A
1163.0
1820.7
Int'l units/100 g dry matter


Total Vit. C
47.9
26.9
mg/100 g dry matter


Vitamin E
3.4
7.7
Int'l units/100 g dry matter


Inositol
218.1
131.5
mg/100 g dry matter


Thiamine
0.13
0.07
mg/100 g dry matter


Folic acid
0.11
0.04
mg/100 g dry matter


Arginine
6.6
7.1
g/100 g protein


Histidine
1.2
1.4
g/100 g protein


Isoleucine
10.5
11.0
g/100 g protein


Leucine
8.9
10.0
g/100 g protein


Lysine
13.3
13.6
g/100 g protein


Methionine
2.7
2.8
g/100 g protein


Phenylalanine
5.5
5.0
g/100 g protein


Threonine
2.5
3.2
g/100 g protein


Tryptophan
0.9
0.7
g/100 g protein


Valine
2.9
3.4
g/100 g protein









Because the addition of feces to an animal diet may adversely affect growth (Acker et al., 1959), and because of public health considerations, offal used for feeding purposes may be treated to reduce the bacterial load (Table 58). There are high levels of ash content (calcium and phosphorus) and vitamins present in offal (Table 59). It appears that poultry offal is a significant source of vitamins, minerals, and possibly unidentified growth factors (Acker et al., 1959).
One way to treat poultry by-products is by rendering, which includes five phases:

    
    
        Storage of raw materials
        Cooking and drying (sterilization)
        Condensation
        Fat extraction
        Meal handling.
    
    


Poultry blood, feathers and offal, hatchery wastes, and dead birds reach the reactor (cooker) in different ways. Hydrolysis and sterilization occur in the cooker where the materials are heated to an established temperature and pressure for a given time. Then, the material is dried at the lowest possible temperature to preserve the quality of the product. Condensation of the vapors is required according to environmental regulations. The end product after drying is ground and sieved. Finally, the product prepared this way can have a fat content higher than 16%; therefore, fat extraction (e.g., the lard drains through the perforated false bottom to an adjacent tank) is required to ensure a lower fat content of 10-12%. The extracted fat can be used as an addition for feed and for other purposes (El Boushy and Van der Poel, 1994).
Sterilization occurs during cooking. Drying is accomplished in a separate drier. Two different types of driers have been used: the disc drier and the flash drier. The flash drier is the most common with benefits such as lower floor space, heating made by oil or gas, and a high-quality end-product (El Boushy and Van der Poel, 1994).
The rendering process can be used to treat different wastes or generate different products such as:

    
    
        Feather meal (FM), using chicken feathers only.
        Poultry by-product meal or offal meal, from offal (viscera, heads, feet, and blood).
        Mixed poultry by-product meal (PBM), from the mixture of poultry offal and chicken feathers.
    
    


The composition and nutritional value for feather meals and poultry by-product meals using different processing conditions are shown in Tables 60-63.







TABLE 60







Composition of poultry by-product meal











% Total weight
Fresh
Dry matter















Moisture
6.1
—



Crude protein
54.6
58.1



Ether extract
14.9
15.9



Crude fiber
0.8
0.9



Ash
17.0
18.1



Nitrogen free extract
6.6
7.0



Calcium
8.0
8.5



Phosphorus
3.0
3.2

















TABLE 61







Offal meals composition using rendering process in different


industrial plants (McNaughton et al., 1977)











Plant 1
Plant 2
Plant 3
















Crude protein
53.99
53.10
54.01



Crude fat
25.34
25.20
24.70



Ash
5.52
5.96
6.06



Moisture
11.15
11.01
9.98



Crude fiber
4.00
4.73
5.25



Calcium
1.46
1.65
1.78



Phosphorus
1.00
1.08
1.10







Values in percentage of total weight













TABLE 62







Amino acid content of feed from different poultry waste


processes (El Boushy and Van der Poel, 1994)











Amino
FM
FM
PBM
PBM


acid
(batch)
(continuous)
(batch)
(continuous)





ASP
5.90
5.75
5.20
5.17


THR
4.05
4.35
2.40
2.33


SER
7.50
9.25
2.70
2.70


GLU
10.10
10.35
9.83
9.70


PRO
9.55
8.85
6.43
6.50


GLY
6.75
6.85
7.87
7.40


ALA
5.35
4.75
4.43
4.93


VAL
5.40
5.80
2.87
3.03


CYS
2.60
3.00
0.63
0.60


MET
0.50
0.40
1.07
1.43


ILE
4.15
4.25
2.23
2.30


LEU
7.00
7.25
4.20
4.37


TYR
2.35
2.40
1.80
2.00


PHE
4.30
4.10
2.40
2.53


LYS
1.80
1.90
3.70
3.80


HIS
0.60
0.55
1.10
1.20


ARG
6.65
6.60
4.77
4.77


Crude protein
84.55
86.40
63.63
64.76












FM Feather meal
(batch)
30-60 min, 207-690 kPa, ~150° C.



(continuous)
6-15 min, 483-690 kPa, ~150° C.








PBM
Poultry by-product meal (blood, feathers and offal),



batch or continuous, 30-40 min, 380 kPa, 142° C.













TABLE 63







Amino acid content and availability of different


poultry wastes (El Boushy and Van der Poel, 1994)












FM
Availability
PBM
Availability

















ASP
5.02
56
5.46
67



GLU
7.96
62
8.00
77



SER
6.73
64
6.09
81



HIS
0.55
59
1.08
72



GLY
4.47
—
6.59
—



THR
3.36
62
3.22
76



ALA
4.85
78
4.35
78



ARG
5.44
77
5.45
84



TYR
2.23
65
2.52
77



VAL
6.41
75
4.81
77



MET
0.79
65
1.14
77



PHE
3.89
77
3.63
79



ILE
4.15
78
3.25
79



LEU
6.19
73
5.78
78



LYS
1.57
64
2.81
77



PRO
9.39
71
6.13
77



CYS
4.26
65
2.43
62










Feather meal contains about 85% of crude protein; it is rich in cysteine, threonine and arginine, but deficient in methionine, lysine, histidine, and tryptophan (El Boushy and Roodbeen, 1980). Adding synthetic amino acids or other materials rich in the latter amino acids would improve the quality of the product. At high pressures, the chicken feathers tend to “gum” giving a non free-flowing meal.
Offal and feathers were obtained from the Texas A&M Poultry Science Department. The offal used contains bones, heads, beaks, feet, and internal organs (e.g., heart, lungs, intestine, liver). The offal was blended for 10 min in an industrial blender, collected in plastic bottles and finally frozen at −4° C. for later use. Samples of this blended material were used to obtain the moisture content, the total nitrogen (estimate of the protein fraction), and the amino acid content to characterize the starting material. Feathers were washed several times with water, air-dried at ambient temperature, dried at 105° C. and finally ground using a Thomas-Wiley laboratory mill (Arthur H. Thomas Company, Philadelphia, Pa.), and sieved through a 40-mesh screen.
The experiments were performed in two autoclave reactors (12-L, and 1-L) with a temperature controller and a mixer powered by a variable-speed motor. The conditions studied were established from previous experiments with both chicken feathers and chicken offal. The treatment conditions include temperature, raw material concentration (dry offal+feathers/L), calcium hydroxide loading (g Ca(OH)2/g dry offal+feathers), and time. Samples were taken from the reactor at different times and then they were centrifuged to separate the liquid phase from the residual solid material.
A group of steps were followed such that data were collected for the different intermediate products for the process shown in FIG. 35.
The raw offal was 33.4% dry material and 66.6% moisture. The crude protein concentration of the dry offal was −34% (offal TKN 5.40%) and the ash content was −10%; the remaining 56% was fiber and fat. Amino acid analysis (Table 64) of the solid raw offal shows a good balance for all amino acids. The total protein content from the amino acid analysis is 26 g protein/100 g dry offal (Table 65). Considering that some amino acids were destroyed during the acid hydrolysis used in the HPLC determination and that Kjeldhal (TKN) values approximate the protein content, these two values are similar.







TABLE 64







Amino acid analysis for the dry raw offal













Percentage




Concentration
(g amino



Amino acid
(mg/L)
acid/100 g protein)















ASP
29.565
9.900



GLU
50.559
16.930



SER
12.453
4.170



HIS
5.826
1.951



GLY
22.557
7.553



THR
12.409
4.155



ALA
20.943
7.013



ARG
22.753
7.619



TYR
10.015
3.354



VAL
15.172
5.080



MET
6.894
2.309



PHE
13.456
4.506



ILE
13.100
4.387



LEU
28.257
9.462



LYS
20.266
6.786



PRO
14.409
4.825

















TABLE 65







Determination of amino acid content for dry raw offal sample










Variable
Value














Total amino acid concentration (mg/L)
298.63



Total mass of amino acid in solid sample (mg)
23.89



Mass of solid sample for analysis (mg)
92



Percent of amino acid in dry sample
26










The chicken feathers were 92% dry material and 8% moisture. The crude protein concentration of the dry feathers was about 95.7% (feathers TKN 15.3%); the remaining 4.3% was fiber and ash.
Experiment 1.
Whole Offal Hydrolysis
Experiment 1 compares the protein solubilization of the complete offal sample (bones, heads, beaks, feet, and internal organs) with a sample that only used internal organs, which was conducted previously (Chapter V). The conditions used in Experiment I were 75° C., 0.10 g lime/g offal, and 40 g dry offal/L. The experimental conditions studied and variables measured are summarized in Table 66.







TABLE 66







Experimental conditions and variables measured to determine


the protein solubilization of the offal sample with bones,


heads, beaks, feet, and internal organs










Variable
Value














Temperature (° C.)
75



Mass of Ca(OH)2 (g)
3.5



Mass of Offal (g)
102.1



Volume of water (mL)
850



Lime loading (g Ca(OH)2/g dry offal)
0.103



Dry offal concentration (g dry offal/L)
40.05



Residual solid (g)
14.2










Table 67 shows the total nitrogen content in the centrifuged liquid samples as a fraction of time for this experiment. On the basis of the average TKN for dry offal (5.40%), the protein hydrolysis conversions were estimated and given in Table 68.







TABLE 67







Protein and mineral content of raw offal and products after lime hydrolysis


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Condition
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















Dry Offal
5.3995
0.6269
0.9181
0.3845
0.0622
3150
59
493
46
10


Liquid 30 min
0.1189
0.0041
0.0311
0.0539
0.001
104
0
11
0
0


Liquid 90 min (*)
0.1925
0.0187
0.0321
0.2
0.0031
104
2
9
2
0


Liquid 90 min
0.1145
0.0041
0.0311
0.0487
0.001
104
0
3
0
0


Dry residual solid
2.5867
0.5606
0.1005
4.1793
0.1078
560
97
187
58
15





(*) Non-centrifuged sample.













TABLE 68







Percentage conversion of the total TKN to soluble TKN










Sample
Conversion














Centrifuged liquid 30 min
59.4



Non-centrifuged liquid 90 min
96.2



Centrifuged liquid 90 min
57.2










At the condition studied, the conversion of nitrogen in the solid phase to the liquid phase was 60% efficient. This value is lower than the one obtained for the same conditions in the previous example but it can be explained by the presence of bones, heads, beaks, and feet, which were not present before. These parts contain higher percentage of ash, minerals, and non-soluble components that reduce the efficiency of the hydrolysis process. The protein hydrolysis did not change between 30 min and 90 min (Table 68), similar to previous results; 30 min is the recommended time to avoid possible degradation of the heat-sensitive amino acids. No important loss of nitrogen occurred during the hydrolysis (96.2% is accounted for in the non-centrifuged sample).
An important reduction (approximately 50%) of protein in the solid is achieved, going from 33.7% in the raw offal to 16.2% (similar to the 13.3% value obtained from the amino acid analysis, Table 69) in the residual solid after lime treatment. There is also a 58% weight reduction of dry solid due to solubilization of amino acids and other soluble components present in the raw offal. This residual solid is stable, with no strong odors, and it has a well-balanced amino acid content (Table 70) that meets, or exceeds, the essential amino acids requirements of the animals during their growth phase.







TABLE 69







Determination of amino acid content for residual


solid after lime treatment










Variable
Value














Total amino acid concentration (mg/L)
180.50



Total mass of amino acid in solid sample (mg)
13.54



Mass of solid sample for analysis (mg)
102



Percent of amino acid in dry sample
13.27

















TABLE 70







Amino acid analysis for the residual


solid after lime treatment













Percentage




Concentration
(g amino



Amino acid
(mg/L)
acid/100 g protein)















ASP
19.289
10.686



GLU
25.776
14.280



SER
8.512
4.716



HIS
4.314
2.390



GLY
9.178
5.085



THR
8.314
4.606



ALA
10.392
5.757



ARG
12.771
7.075



TYR
7.805
4.324



VAL
10.546
5.843



MET
4.967
2.752



PHE
10.376
5.749



ILE
9.545
5.288



LEU
20.762
11.502



LYS
9.858
5.462



PRO
8.096
4.485










The treatment of chicken offal with lime hydrolyzes the protein present into small peptides and free amino acids, which are soluble in water. Therefore, the 60% TKN conversion from the solid phase to the liquid phase represents the efficiency of recovering protein in the liquid phase. Table 71 shows the amino acid balance for this centrifuged liquid.







TABLE 71







Amino acid analysis for the centrifuged liquid sample (30 min)













Percentage




Concentration
(g amino



Amino acid
(mg/L)
acid/100 g protein)















ASP
69.983
3.530



GLU
129.448
6.529



ASN
3.937
0.199



SER
98.378
4.962



GLN
26.346
1.329



HIS
25.379
1.280



GLY
69.551
3.508



THR
73.033
3.684



CIT
54.309
2.739



B-ALA
4.170
0.210



ALA
147.275
7.428



TAU
200.813
10.129



ARG
162.465
8.195



TYR
93.992
4.741



CYS-CYS
102.601
5.175



VAL
80.385
4.055



MET
51.049
2.575



TRP
36.910
1.862



PHE
86.256
4.351



ILE
74.689
3.767



LEU
179.141
9.036



LYS
136.399
6.880



PRO
76.073
3.837







Total amino acid concentration 1982.6 mg/L.






A comparison of the amino acid content of the raw offal, the centrifuged liquid product, and the residual solid (Table 72) shows that the amino acid contents in the centrifuged liquid and the residual solid are comparable to the raw offal. This implies that the solubilization of all amino acids occurs at a similar rate and that there is little destruction of specific amino acids for the conditions studied.







TABLE 72







Comparison of amino acid content for the different


materials during lime treatment of chicken offal














Residual
Centrifuged



Amino acid
Offal
solid
Liquid*
















ASP
9.90
10.69
4.50



GLU
16.93
14.28
8.33



SER
4.17
4.72
6.33



HIS
1.95
2.39
1.63



GLY
7.55
5.08
4.48



THR
4.16
4.61
4.70



ALA
7.01
5.76
9.48



ARG
7.62
7.08
10.46



TYR
3.35
4.32
6.05



VAL
5.08
5.84
5.17



MET
2.31
2.75
3.29



PHE
4.51
5.75
5.55



ILE
4.39
5.29
4.81



LEU
9.46
11.50
11.53



LYS
6.79
5.46
8.78



PRO
4.83
4.49
4.90







*Considering only the amino acids present in the solid analysis.






The treatment of chicken offal with lime at medium temperature and time reduces the amount of microorganisms present in the liquid phase. Rapid evaporation of the liquid is essential because the liquid medium contains all the nutritional requirements for bacterial growth.
The amino acid analysis of the samples (Table 73) shows again a very well balanced product that meets, or exceeds, the essential amino acids requirements of the animals during their growth phase. A slightly low value is obtained for histidine.







TABLE 73







Amino acid analysis of raw material and products, compared with the essential


amino acids requirements for various domestic animals (whole offal)





















Centrifuged

Residual


Amino acid
Catfish
Dogs
Cats
Chickens
Pigs
liquid
Solid offal
Solid


















ASN





0.20




GLN





1.33


ASP





3.53
9.90
10.69


GLU





6.53
16.93
14.28


SER





4.96
4.17
4.72


HIS
1.31
1.00
1.03
1.40
1.25
1.28
1.95
2.39


GLY





3.51
7.55
5.08


THR
1.75
2.64
2.43
3.50
2.50
3.68
4.16
4.61


ALA





7.43
7.01
5.76


ARG
3.75
2.82
4.17
5.50
0.00
8.19
7.62
7.08


VAL
2.63
2.18
2.07
4.15
2.67
4.05
5.08
5.84


CYS
2.00+
2.41+
3.67+
4.00+
1.92+
5.18
ND
ND


MET
2.00+
2.41+
2.07
2.25
1.92+
2.57
2.31
2.75


TYR
4.38*
4.05*
2.93*
5.85*
3.75*
4.74
3.35
4.32


PHE
4.38*
4.05*
1.40
3.15
3.75*
4.35
4.51
5.75


ILE
2.28
2.05
1.73
3.65
2.50
3.77
4.39
5.29


LEU
3.06
3.27
4.17
5.25
2.50
9.04
9.46
11.50


LYS
4.47
3.50
4.00
5.75
3.58
6.88
6.79
5.46


TRIP
0.44
0.91
0.83
1.05
0.75
1.86
ND
ND


PRO





3.84
4.83
4.49





*Cysteine + Methionine


+Tyrosine + Phenylalanine


ND Not determined


Values expressed as g individual amino acid per 100 g total amino acids.






Experiment 2.
Offal and Feather Processing
Chicken feathers and offal have different compositions and their main components behave differently during protein hydrolysis with lime. Keratin protein is harder to hydrolyze than the proteins in offal, requiring longer times or higher temperatures and lime concentrations. The residual wastes from slaughterhouses often contain mixtures of offal and feathers making the treatment of this mixture a possibility for obtaining a protein-rich product. Two products could be generated: one with a well-balanced amino acid content that could meet the amino acid requirements for various monogastric domestic animals (from the offal), and a second one for ruminants (from the feathers).
Hydrolysis of a chicken feather/offal mixture was studied using the process shown in FIG. 35. The initial treatment of the mixture was done to hydrolyze mainly the protein present in offal to obtain a liquid product and a residual solid. Bubbling the liquid product with CO2 precipitated CaCO3 (that can be converted back to lime) and reduced the concentration of Ca in the liquid phase. The final evaporation of this liquid yields the first solid amino acid-rich product.
The residual solid of Phase 1 was returned to the reactor to further treat with lime at longer times (different conditions) to promote the hydrolysis of the chicken feather protein. Steps similar to the Phase 1 will be followed to obtain the second product.
Experiments AI, B1, and C1 used Condition 1 whereas Experiments A2, B2, and C2 used Condition 2.
The experimental conditions studied and variables measured during Experiment 2 are summarized in Table 74. A ratio of 17.5 g wet offal/7 g wet feathers was used because it is a normal value in the waste generation of a slaughterhouse.







TABLE 74







Experimental conditions and variables measured to determine the protein


solubilization of the offal/feather mixture













Variable
Exp. A1
Exp. A2
Exp. B1
Exp. B2
Exp. C1
Exp. C2
















Temperature (° C.)
50
75
75
75
75
100


Mass of Ca(OH)2 (g)
36
41.4
20.7
20.7
4.8
2.7


Mass of offal (g)
685

343

91.3


Mass of feathers (g)
274
410
137
211.8
36.5
48.7


Volume of water (mL)
6000
3000
3000
2000
800
800


Ca(OH)2 (g/d dry offal)
0.075
0.101
0.086
0.098
0.075
0.055


Dry matter (g/L)
80.08
136.53
80.13
105.79
80.02
60.81


Dry Offal (g/L)
38.06

38.12

38.05


Total TKN (g)
50.94

25.48

6.79


TKN (%)
10.60

10.60

10.60









Table 75 shows the total nitrogen content in the centrifuged liquid samples as a function of time for this experiment. The average TKN for dry offal (5.40%) and chicken feathers (15.3%) gave a mixture initial TKN of 10.6%. Protein hydrolysis conversions were estimated and are given in Table 76 and Table 77. Table 76 considers the conversion with respect to the offal first (Condition 1) and feathers second (Condition 2), whereas Table 77 gives the conversion with respect to the initial TKN of the mixture. At the conditions studied, the highest conversion of nitrogen in the solid phase to the liquid phase was 60%.







TABLE 75







Total Kjeldhal nitrogen content in the centrifuged liquid phase as a


function of time for Experiment 2 (offal/feathers mixture)













Time (min)
Exp. A1
Exp. A2
Exp. B1
Exp. B2
Exp. C1
Exp. C2
















5
0.1126
0.1015
—
0.1183
—
—


10
0.1210
—
0.1109
—
—
—


15
0.1154
0.0973
0.1238
0.1262
—
—


30
0.1182
0.1126
0.1182
0.1431
—
—


60
—
0.1514
0.1349
0.1723
0.2300
—


120
—
0.2188
—
0.2299
—
0.2600





TKN in g nitrogen/100 g liquid sample.













TABLE 76







Percentage conversion of the total TKN to soluble TKN for Experiment 2,


with respect to offal (A1, B1 and C1) and feathers (A2, B2 and C2)


TKN respectively













Time (min)
Exp. A1
Exp. A2
Exp. B1
Exp. B2
Exp. C1
Exp. C2
















5
59.2
7.9
—
12.3
—
—


10
63.6
—
58.2
—
—
—


15
60.6
7.6
64.9
13.1
—
—


30
62.1
8.7
62.0
14.8
—
—


60
—
11.8
70.8
17.9
120.9
—


120
—
17.0
—
23.8
—
26.9
















TABLE 77







Percentage conversion of the total TKN to soluble TKN for


Experiment 2 (offal/feathers mixture)













Time (min)
Exp. A1
Exp. A2
Exp. B1
Exp. B2
Exp. CI
Exp. C2
















5
14.3
6.0
—
9.3
—
—


10
15.4
—
14.1
—
—
—


15
14.7
5.7
15.7
9.9
—
—


30
15.0
6.6
15.0
11.2
—
—


60
—
8.9
17.2
13.5
29.3
—


120
—
12.9
—
18.0
—
30.7


Total

27.9

35.2

60









Based on the data in Table 76, no significant effect on conversion occurs when changing the temperature from 50 to 75° C. Results from Experiments Al and B 1 show a higher conversion at 60 min compared to 30 min; this is expected because keratin protein hydrolyzes slower and continues to react while contacting the lime. Also, comparing Table 68 and Table 76, similar results are obtained for the conversion of the offal/chicken feather mixture as for offal alone; hence, the offal present in the mixture hydrolyzes at the same rate as the offal alone. At the temperatures studied in Experiments Al and B 1, the hydrolysis of chicken feathers is relatively slow compare to offal. The protein hydrolysis increases significantly by changing the temperature from 75 to 100° C. (Experiment C1) for Condition 1. This result is explained by the higher conversion expected for the chicken feathers at this condition, 60% for chicken feathers hydrolysis at 2 h (Chang and Holtzapple, 1999).
Results from Experiments A2 and B2 show that the initial “pretreatment” of the chicken feathers in a mixture with chicken offal slightly increases the hydrolysis conversion for the feathers (17% to 23.8%), and that higher temperatures or longer times might be required to completely hydrolyze the chicken feathers. Results from Experiment C2 show a higher conversion at 100° C. compared to 75° C. From the Chang and Holtzapple study, an even higher temperature or a longer reaction time could be used to further increase the protein hydrolysis.
Tables 78-80 show the total nitrogen and mineral content of the samples from the different steps of the lime treatment process of the offal/feather mixture. A slight reduction of calcium content (8%) is obtained after bubbling the liquid with CO2 until a pH of  ̃6 is achieved. This reduction is accompanied by a similar reduction of nitrogen content (Table 78). These results show that calcium precipitation with CO2 is a very inefficient process for the conditions studied.







TABLE 78







Protein and mineral content of products after lime hydrolysis for Experiments A1 & A2


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn



(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)





















With solids (30 min)
0.4257











Liquid 1(30 min)
0.1182
0.0093
0.0404
0.0746
0.001
259
0
3
1
0


After bubbling
0.1098
0.0083
0.0352
0.0684
0
207
0
2
1
0


With solids (2 h)
0.5420


Liquid 2 (2 h)
0.2188
0.0041
0.0197
0.1523
0
155
1
6
1
0


After bubbling
0.2108
0.0031
0.0176
0.1503
0
145
1
2
1
0


Residual Solid 1
9.0254
0.571
0.3119
4.0974
0.0756
3264
104
210
35
13


Residual Solid 2
7.9002
0.2974
0.1492
5.6684
0.1109
2694
104
301
31
16
















TABLE 79







Protein and mineral content of products after lime


hydrolysis for Experiments B1 & B2


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn



(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















With solids (60 min)
0.4257











Liquid 1 (60 min)
0.1349
0.0104
0.0383
0.0984
0.001
259
1
5
1
0


With solids (2 h)
0.5926


Liquid 2 (2 h)
0.2299
0.0031
0.0166
0.1668
0
135
1
2
1
0


Residual Solid 1
8.7163


Residual Solid 2
8.0355
0.313
0.0705
5.9482
0.0839
2518
77
166
20
9
















TABLE 80







Protein and mineral content of products after


lime hydrolysis for Experiments C1 & C2


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn



(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















Liquid 1 (60 min)
0.23
0
0.04
0.1
0
228
2
1
0
0


Liquid 2 (2 h)
0.26
0
0.01
0.14
0
83
1
1
0
0


Residual Solid 1
12.79
0.3
0.32
2.92
0.05
1617
73
152
19
5


Residual Solid 2
9.77
0.53
0.09
4.29
0.09
819
95
269
24
9


Final product
11.71
0.12
0.55
5.17
0.01
2912
38
21
11
8









Table 79 shows that after the second lime treatment, the protein content in the solid goes from 10.6% (TKN) in the raw mixture to 7.9% (TKN) in the final residual solid, about a 25% reduction. Also, there is approximately 35% reduction in total dry weight (soluble matter). This residual solid is stable, with no strong odors, a relatively high concentration of calcium ( ̃6% for all cases), and an amino acid content poor in several amino acids that are required for animal growth; similar to the residual obtained for chicken feathers only.
Because the concentration of calcium is high in Residual Solid #1, for all the cases, a lower amount of lime might be added to the second lime treatment with a similar result for the protein hydrolysis conversion.
The concentrations of all the minerals are compared for all the cases studied (Tables 78-80). The nitrogen content in the Centrifuged Liquid #1 and #2 increases with the highest temperature. The mineral content (phosphorus, potassium, and sodium) decreases from Liquid #1 to Liquid #2 as more salts are solubilized with temperature and time.
Tables 81-83 show the amino acid content for the different liquid products obtained at the conditions studied. For Experiments A2 and B2 the samples were hydrolyzed with HCL for 24 h before the amino acid analysis to determine the total amino acids concentration from the chicken feather hydrolysis. In Experiment C2 no hydrolysis was performed for comparison purposes.







TABLE 81







Amino acid analysis for the centrifuged liquid


sample in Experiments A1 and A2










Experiment A1
Experiment A2













Percentage 

Percentage




(g amino

(g amino



Concentration
acid/100 g
Concentration
acid/100 g


Amino acid
(mg/L)
protein)
(mg/L)
protein)














ASP
205.70
5.12
412.20
7.50


GLU
454.38
11.30
649.67
11.81


ASN
9.92
0.25
40.51
0.74


SER
235.14
5.85
351.29
6.39


GLN
0.00
0.00
0.00
0.00


HIS
50.93
1.27
0.00
0.00


GLY
170.00
4.23
365.21
6.64


THR
149.34
3.72
131.27
2.39


CIT
53.03
1.32
99.38
1.81


B-ALA
6.44
0.16
4.72
0.09


ALA
276.72
6.88
443.72
8.07


TAU
389.12
9.68
106.69
1.94


ARG
298.98
7.44
256.01
4.66


TYR
178.99
4.45
378.28
6.88


CYS-CYS
109.61
2.73
127.71
2.32


VAL
164.71
4.10
490.55
8.92


MET
110.56
2.75
99.93
1.82


TRP
68.81
1.71
46.19
0.84


PHE
162.55
4.04
236.89
4.31


ILE
141.70
3.52
334.24
6.08


LEU
351.04
8.73
578.80
10.53


LYS
305.46
7.60
283.56
5.16


PRO
126.91
3.16
62.32
1.13


Total Conc.
4020.04

5499.14
















TABLE 82







Amino acid analysis for the centrifuged liquid


sample in Experiments B1 and B2










Experiment B1
Experiment B2













Percentage

Percentage




(g amino

(g amino



Concentration
acid/100 g
Concentration
acid/100 g


Amino acid
(mg/L)
protein)
(mg/L)
protein)














ASP
208.38
4.88
606.53
8.23


GLU
455.89
10.69
788.25
10.70


ASN
9.39
0.22
0.00
0.00


SER
245.38
5.75
943.75
12.81


GLN
20.55
0.48
0.00
0.00


HIS
51.98
1.22
0.00
0.00


GLY
194.49
4.56
956.65
12.98


THR
161.33
3.78
166.24
2.26


CIT
67.51
1.58
0.00
0.00


B-ALA
9.57
0.22
0.00
0.00


ALA
300.78
7.05
387.08
5.25


TAU
391.07
9.17
0.00
0.00


ARG
329.20
7.72
546.22
7.41


TYR
204.69
4.80
274.13
3.72


CYS-CYS
74.44
1.74
0.00
0.00


VAL
171.31
4.02
401.03
5.44


MET
118.50
2.78
102.84
1.40


TRP
41.72
0.98
0.00
0.00


PHE
161.73
3.79
370.28
5.03


ILE
138.92
3.26
330.31
4.48


LEU
363.99
8.53
684.05
9.28


LYS
345.67
8.10
106.63
1.45


PRO
199.60
4.68
704.17
9.56


Total Conc.
4266.10

7368.15
















TABLE 83







Amino acid analysis for the centrifuged liquid sample in Experiments


C1 and C2










Experiment C1
Experiment C2













Percentage

Percentage



Con-
(g amino
Con-
(g amino



centration
acid/100 g
centration
acid/100 g


Amino acid
m/L
protein)
m/L
protein)














ASP
280.42
4.81
73.39
6.95


GLU
675.71
11.59
148.71
14.08


ASN
14.89
0.26
0.88
0.08


SER
244.52
4.20
99.68
9.44


GLN
0.00
0.00
0.00
0.00


HIS
80.50
1.38
0.00
0.00


GLY
249.11
4.27
91.98
8.71


THR
227.13
3.90
6.41
0.61


CIT
238.91
4.10
75.04
7.10


B-ALA
6.61
0.11
0.00
0.00


ALA
438.12
7.52
106.95
10.12


TAU
199.22
3.42
22.59
2.14


ARG
262.88
4.51
39.32
3.72


TYR
97.79
1.68
13.70
1.30


CYS—CYS
181.57
3.12
47.73
4.52


VAL
293.99
5.04
56.11
5.31


MET
148.91
2.55
14.41
1.36


TRP
113.75
1.95
0.00
0.00


PHE
258.51
4.44
48.00
4.54


ILE
270.12
4.63
54.45
5.15


LEU
599.13
10.28
107.36
10.16


LYS
408.43
7.01
25.54
2.42


PRO
537.85
9.23
24.20
2.29


Total Conc.
5828.07

1056.46









From Tables 81-83, a comparison of results from Experiments AI, B1, and C1 show similar amino acid contents for all cases; hence, the effect of temperature on the hydrolysis rate is similar for the different individual amino acids. The temperature increases the hydrolysis conversion (100° C. vs. 75° C., Table 76 and Table 77) but does not affect the amino acid content in the lime treatment of the chicken feather/offal mixture.
By comparing Experiments A1, B1, and C1 with the amino acid content for chicken offal only (Table 71), similar results are obtained in all cases. The amino acid content and protein hydrolysis of the chicken offal are not affected by the presence of chicken feathers in the mixture and the hydrolysis of these feathers is relatively small at the conditions studied. The increase in proline for the higher temperature can be explained by the hydrolysis of connecting tissue and bones (in offal) that probably requires higher temperature.
A comparison of results from Experiments A2, B2, and C2 show greater differences in the amino acid content than experiments AI, B1, and C1. The different amounts of non-hydrolyzed offal that remained in Residual Solid #1 for the different temperatures studied can explain these differences.
Table 84 and Table 85 compare the requirements for essential amino acids of various domestic animals with the different products.







TABLE 84







Amino acid analysis of raw material and products, compare


with the essential amino acids requirements for various


domestic animals (offal/feathers mixture Condition 1)















Amino acid
Catfish
Dogs
Cats
Chickens
Pigs
Exp A1
Exp B1
Exp C1


















ASN





0.25
0.22
0.26


GLN





0.00
0.48
0.00


ASP





5.12
4.88
4.81


GLU





11.30
10.69
11.59


SER





5.85
5.75
4.20


HIS
1.31
1.00
1.03
1.40
1.25
1.27
1.22
1.38


GLY





4.23
4.56
4.27


THR
1.75
2.64
2.43
3.50
2.50
3.72
3.78
3.90


ALA





6.88
7.05
7.52


ARG
3.75
2.82
4.17
5.50
0.00
7.44
7.72
4.51


VAL
2.63
2.18
2.07
4.15
2.67
4.10
4.02
5.04


CYS
2.00+
2.41+
3.67+
4.00+
1.92+
2.73
1.74
3.12


MET
2.00+
2.41+
2.07
2.25
1.92+
2.75
2.78
2.55


TYR
4.38*
4.05*
2.93*
5.85*
3.75*
4.45
4.80
1.68


PHE
4.38*
4.05*
1.40
3.15
3.75*
4.04
3.79
4.44


ILE
2.28
2.05
1.73
3.65
2.50
3.52
3.26
4.63


LEU
3.06
3.27
4.17
5.25
2.50
8.73
8.53
10.28


LYS
4.47
3.50
4.00
5.75
3.58
7.60
8.10
7.01


TRP
0.44
0.91
0.83
1.05
0.75
1.71
0.98
1.95


PRO





3.16
4.68
9.23





*Phenylalanine + Tyrosine


+Cysteine + Methionine


All values arc in g amino acid/100 g protein.













TABLE 85







Amino acid analysis of raw material and products, compare


with the essential amino acids requirements for various


domestic animals (offal/feathers mixture Condition 2)















Amino acid
Catfish
Dogs
Cats
Chickens
Pigs
Exp A2
Exp B2
Exp C2


















ASN





0.74
0.00
0.08


GLN





0.00
0.00
0.00


ASP





7.50
8.23
6.95


GLU





11.81
10.70
14.08


SER





6.39
12.81
9.44


HIS
1.31
1.00
1.03
1.40
1.25
0.00
0.00
0.00


GLY





6.64
12.98
8.71


THR
1.75
2.64
2.43
3.50
2.50
2.39
2.26
0.61


ALA





8.07
5.25
10.12


ARG
3.75
2.82
4.17
5.50
0.00
4.66
7.41
3.72


VAL
2.63
2.18
2.07
4.15
2.67
8.92
5.44
5.31


CYS
2.00+
2.41+
3.67+
4.00+
1.92+
2.32
0.00
4.52


MET
2.00+
2.41+
2.07
2.25
1.92+
1.82
1.40
1.36


TYR
4.38*
4.05*
2.93*
5.85*
3.75*
6.88
3.72
1.30


PHE
4.38*
4.05*
1.40
3.15
3.75*
4.31
5.03
4.54


ILE
2.28
2.05
1.73
3.65
2.50
6.08
4.48
5.15


LEU
3.06
3.27
4.17
5.25
2.50
10.53
9.28
10.16


LYS
4.47
3.50
4.00
5.75
3.58
5.16
1.45
2.42


TRP
0.44
0.91
0.83
1.05
0.75
0.84
0.00
0.00


PRO





1.13
9.56
2.29





*Phenylalanine + Tyrosine


+Cysteine + Methionine


All values arc in g amino acid/100 g protein.






For the liquid product obtained after the first hydrolysis of the chicken feather/offal mixture, the tabulated results imply that the solubilized protein meets, or exceeds, the essential amino acids requirements of the animals during their growth phase. Histidine will be the limiting amino acid for this product.
On the other hand, the product after the second hydrolysis (feathers), the values for threonine, cysteine+methionine, tryptophan, and especially lysine and histidine are lower than the requirements making this a poor product for monogastric animal nutrition. However, it is suitable for ruminants.
Experiment 3.
Calcium Recovery and Recycle
The use of calcium hydroxide as the alkaline material produces a relatively high calcium concentration in the centrifuged liquid solution. Because some calcium salts have low solubility, calcium can be recovered by precipitating it as calcium carbonate, calcium bicarbonate, or calcium sulfate (gypsum).
Calcium carbonate is preferred because of its low solubility (0.0093 g/L, solubility product for CaCO3 is 8.7×10−9). In contrast, the solubility of CaSO4 is 1.06 g/L, with a solubility product of 6×10−5. Also, it is easier to regenerate Ca(OH)2 from calcium carbonate than from calcium sulfate. Because CaSO4 is a more soluble material and gypsum is more difficult to recycle, the use of CaCO3 as the precipitate is a more efficient process.
When CO2 is bubbled into the centrifuged solution, carbonic acid (H2CO3) is formed. The carbonic acid is a weak diprotic acid with pKa1=6.37 and pKa2=10.25. An equilibrium between H2CO3, HCO3−, and CO32− is generated and the fraction of each component in the mixture is a function of pH. Because Ca(HCO3)2 is water-soluble (166 g/L of water, solubility product 1.08), the precipitation efficiency of the process is also a function of pH.
To measure and study calcium recovery by CO2 bubbling; centrifuged liquid products from the hydrolysis process of chicken feathers and offal were collected in plastic bottles and kept at 4° C. for later use. A known volume of the centrifuged liquid material (400 mL) was placed into an Erlenmeyer flask with a magnetic stirring bar (constant stirring), and CO2 was bubbled from a pressurized container. As pH decreased, liquid samples ( ̃10 mL) were collected and centrifuged. Total nitrogen and calcium content were measured in the clarified liquid. Samples with different initial pH were used to study how this parameter affects precipitation efficiency.
FIG. 36 shows the calcium and total nitrogen content as a function of pH for two different samples: one from chicken offal hydrolysis (C1) and the other from the chicken feathers hydrolysis (C2). In both cases, TKN concentration remains constant, implying that no nitrogen is lost during the precipitation of calcium.
FIG. 36 also shows that calcium concentration decreases to a minimum at pH ̃9 (calcium recovery between 50 and 70%), and increases at lower pHs. The increase in calcium concentration is expected because of the high solubility of calcium bicarbonate and the conversion of carbonate to bicarbonate and carbonic acid at low pH (8 and lower). The initial pH for the centrifuged liquid shown in FIG. 36 is relatively high (10.2 and 11.1 respectively); in both cases the equilibrium between the carbonic species is in a zone with relatively high carbonate concentration (pKa2=10.25).
FIG. 37 on the other hand, shows the calcium and total nitrogen content of samples with a relatively low initial pH ( ̃9.2). Because the samples collected were well inside the equilibrium zone between carbonic acid and bicarbonate, no calcium could be recovered as a precipitate (calcium bicarbonate solubility).
Experiment 4
Preservation of Chicken Waste Under Alkaline Conditions
The chicken offal and feathers described previously in this example were used as raw materials for another set of experiments. Experiments were performed in l-L Erlenmeyer flasks at ambient temperature and with no mixing; to avoid unpleasant odors, flasks were placed inside the hood. Calcium hydroxide loading (g Ca(OH)2/g dry offal+feathers) was varied, to determine the lime required to preserve this waste material mixture. Generation of strong bad odors (fermentation products) is considered as the end-point of the study.
Duplicate experiments were run under the same conditions. Samples were taken from the reactor at different times and were centrifuged to separate the liquid phase from the solid material. Total nitrogen content and pH were measured in the centrifuged liquid samples.
To determine the lime required for preservation of the chicken waste mixture and to study protein solubilization of the waste material, several experiments were run with different lime loadings, at ambient temperature, and utilizing no mixing. The experimental conditions studied and variables measured are summarized in Table 86.







TABLE 86







Experimental conditions during study of preservation of chicken


feathers and offal mixture














Exp. G1
Exp. G2
Exp. H1
Exp. H2
Exp. I1
Exp. I2

















Temperature
25
25
25
25
25
25


(° C.)


Mass of
3.3
3.3
6.6
6.6
9.9
9.9


Ca(OH)2(g)


Mass of offal
91.3
91.3
91.3
91.3
91.3
91.3


(g)


Mass of
36.5
36.5
36.5
36.5
36.5
36.5


feathers (g)


Volume of
800
800
800
800
800
800


water (ml)


Ca(OH)2
0.052
0.052
0.103
0.103
0.155
0.155


(g/g dry matter)


Dry matter
80.02
80.02
80.02
80.02
80.02
80.02


(g/L)


Dry Offal (g/L)
38.05
38.05
38.05
38.05
38.05
38.05


Total TKN (g)
6.79
6.79
6.79
6.79
6.79
6.79


Total TKN (%)
10.60
10.60
10.60
10.60
10.60
10.60









Table 87 shows the pH variation as a function of time while Table 88 shows the total nitrogen content of the centrifuged liquid.







TABLE 87







pH as a function of time during the preservation study


of chicken offal and feathers mixture













time (d)
Exp. G1
Exp. G2
Exp. H1
Exp. H2
Exp. I1
Exp. I2
















0
9.01
9.12
12.1
12.14
12.1
12.15


1
—
—
11.52
11.56
12.14
12.17


2
—
—
11.16
11.25
12.08
12.14


4
—
—
10.82
11.03
12.03
12.06


7
—
—
10.65
10.85
12.05
12.06


11
—
—
9.05
10.1
12.06
12.09


14
—
—
—
—
12.06
12.1


17
—
—
—
—
12.04
12.07
















TABLE 88







Total Kjeldhal nitrogen content as a function of time during the


preservation study of chicken offal and feathers mixture













time (d)
Exp. G1
Exp. G2
Exp. H1
Exp. H2
Exp. I1
Exp. I2
















0
0.1438
0.1427
0.1002
0.1103
0.0924
0.0991


1
—
—
0.1248
0.1314
0.1325
0.1381


2
—
—
0.1337
0.1337
0.1460
0.1472


4
—
—
0.1348
0.1337
0.1596
0.1630


7
—
—
0.1371
0.1416
0.1835
0.1824


11
—
—
0.1472
0.1427
0.2099
0.2020


14
—
—
—
—
0.2239
0.2251


17
—
—
—
—
0.2297
0.2297





TKN in g nitrogen/100 g liquid sample.






The protein hydrolysis conversions were estimated and are given in Table 89 and Table 90. Table 89 considers the conversion with respect to the offal nitrogen content whereas Table 90 gives the conversion with respect to the initial TKN of the mixture. At the conditions studied, the highest conversion of nitrogen in the solid phase to the liquid phase was  ̃30%.







TABLE 89







Percent conversion in the liquid phase with respect to offal as


a function of time (preservation experiment)













time (d)
Exp. G1
Exp. G2
Exp. H1
Exp. H2
Exp. I1
Exp. I2
















0
75.5692
74.9911
52.6567
57.9644
48.5577
52.0786


1
—
—
65.5844
69.0528
69.6309
72.5738


2
—
—
70.2615
70.2615
76.7253
77.3560


4
—
—
70.8396
70.2615
83.8724
85.6591


7
—
—
72.0482
74.4131
96.4322
95.8541


11
—
—
77.3560
74.9911
110.3058
106.1542


14
—
—
—
—
117.6630
118.2937


17
—
—
—
—
120.7110
120.7110
















TABLE 90







Percent conversion in the liquid phase with respect to


total nitrogen as a function of time (preservation experiment)













time (d)
Exp. G1
Exp. G2
Exp. H1
Exp. H2
Exp. I1
Exp. I2
















0
18.3018
18.1618
12.7527
14.0382
11.7600
12.6127


1
—
—
15.8836
16.7236
16.8636
17.5764


2
—
—
17.0164
17.0164
18.5818
18.7345


4
—
—
17.1564
17.0164
20.3127
20.7454


7
—
—
17.4491
18.0218
23.3545
23.2145


11
—
—
18.7345
18.1618
26.7145
25.7091


14
—
—
—
—
28.4963
28.6491


17
—
—
—
—
29.2345
29.2345









In Table 89, values higher than 100% imply the solubilization of chicken feather protein for the long-term reservation study. Also, a comparison between Experiments H and I correlate a high protein hydrolysis to a high pH. The reduction of pH during the hydrolysis process (Table 87) is related to the generation of new free amino acid values close to 9 were measured the day previous to strong odor generation.
Monitoring pH during the preservation of chicken waste mixture is a viable alternative for keeping a stable (non-fermentative) solution. Based on the results obtained, a pH value of 10.5 could be used as the lower limit for the addition of extra lime to avoid bacterial growth.
Lime is a relatively water insoluble base, and because of this low solubility, it generates mild-alkaline conditions (pH ̃12) in the solid-liquid mixture. The relative low pH reduces the possibility of unwanted degradation reactions, when compared to strong bases (e.g., sodium hydroxide). Lime also promotes the digestion of protein and solubilization into the liquid phase (Table 90), while the chicken waste mixture is preserved.
Chicken offal and feathers can be used to obtain an amino acid-rich product by treating with Ca(OH)2 at temperatures less than 100° C. A simple non-pressurizing vessel can be used for the above process due to the low temperature requirements.
A chicken feather/offal mixture can be used to obtain two amino acid-rich products, one which is well balanced (offal) and a second which is deficient in some amino acids but high in protein and mineral content.
For the first lime treatment of the mixture—runs at 50-100° C.—the spectrum of essential amino acids obtained from the experiments meets or exceeds the requirements for many domestic animals during their growth period. Thus, the amino acid-rich solid product obtained by lime treating chicken offal could serve as a protein supplement for these animals.
For the second lime treatment of the mixture—runs at 75-100° C.—the spectrum of essential amino acids obtained from the experiments is deficient in several amino acids. Thus, the amino acid-rich solid product obtained by the second lime treatment of the chicken feathers/offal mixture could serve as a nitrogen and mineral source for ruminant animals.
Precipitation of calcium carbonate by bubbling CO2 into the centrifuged liquid product gives a calcium recovery between 50 and 70%. A high initial pH is recommended (>10), so that calcium carbonate and not calcium bicarbonate is formed during the process; while a final pH ̃8.8-9.0 ensures a high calcium recovery for lime regeneration. Because CaSO4 is a more soluble material and gypsum is more difficult to recycle, the use of CaCO3 as the precipitate is a more efficient process. Finally, lime solutions hydrolyzed and preserved chicken processing waste, including the keratinous material in chicken feathers. The absence of putrefactive odors, the continuous protein hydrolysis into the liquid phase, and the possibility of continuous monitoring of pH during the conservation of the chicken waste mixture, make the process a feasible alternative for keeping a stable (non-fermentative) solution and preserve carcasses during on-farm storage.
Example 6
Protein Solubilization in Cow Hair
According to the USDA, 188 lbs. of red meat and poultry are consumed per capita each year in the USA, from which  ̃116 lbs. are from beef and pork. Animal slaughter generates large amounts of waste, and animal hair represents between 3 and 7% of the total weight. There is a need and a desire to make better use of waste residues, and to turn them into useful products.
Wet cow hair was obtained from Terrabon Company and then air-dried. To characterize the starting material, the moisture content, the total nitrogen (estimate of the protein fraction), and the amino acid content were determined.
Air-dried hair is used as the starting material for these experiments. Its dry matter content, chemical composition, and amino acid balance are given in Table 91, Table 92, and Table 93, respectively.







TABLE 91







Dry matter content of air-dried cow hair












Sample
Humid Solid (q)
Dry Solid (g)
Dry matter (%)
















1
4.0883
3.8350
93.80



2
3.7447
3.5163
93.90





Average
93.85

















TABLE 92







Protein and mineral content of air-dried cow hair


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)





Hair
14.73
0.0508
0.0197
0.1658
0.029
5244
58
185
50
37
















TABLE 93







Amino acid composition of air-dried cow hair












Amino


Amino




acid
Measured
Literature
acid
Measured
Literature















ASP
6.63
3.0
TYR
2.44
3.4


GLU
14.47
12.2
VAL
6.80
5.5


SER
8.91
7.2
MET
0.71
0.6


HIS
1.29
0.7
PHE
3.09
3.0


GLY
5.52
10.8
ILE
4.20
4.4


THR
7.48
6.6
LEU
9.77
7.7


ALA
4.50
1.0
LYS
5.53
2.1


CYS
ND
13.9
TRP
ND
1.4


ARG
10.98
7.7
PRO
7.68
8.5





ND: Not determined


Values in g AA/100 g total amino acids.






The starting material contains a relatively well-balanced amino acid content, with low levels of histidine, methionine, tyrosine, and phenylalanine. The ash content is very low ( ̃1%) and the crude protein content is high ( ̃92.1%). The starting moisture content is 6.15%.
Experiment 1
Hair Concentration Effect
To determine the effect of the initial hair concentration in the solubilization of protein, experiments were run at different concentrations keeping the temperature and lime loading constant (100° C. and 0.10 g lime/g air-dried hair, respectively). The experimental conditions studied and variables measured are summarized in Table 94.







TABLE 94







Experimental conditions and variables measured for determining


the effect of initial hair concentration in protein solubilization of


cow hair










Hair concentration




(g hair/L)










40
60















Mass of hair (g)
34
51



Volume of water (mL)
850
850



Mass of lime (g)
3.4
5.1



Temperature (° C.)
100
100



Initial temperature (° C.)
101.4
87.1



pH final
9.2
9.8



Residual solid (g)
28.8
44.9



Dissolved solids in 100 mL (g)
1.18
1.92



Protein in 100 mL (g)
0.81
1.04










Table 95 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different hair concentrations. On the basis of the average TKN for air-dried hair (14.73%), the protein hydrolysis conversions are estimated and are given in Table 96.







TABLE 95







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 1 (cow hair)










Air-dried hair




concentration









Time (h)
40 g/L
60 g/L












0
0.0160
0.0327


0.5
0.0185
0.0497


1
0.0435
0.0699


2
0.0718
0.1000


3
0.0754
0.1194


4
0.0868
0.1368


6
0.1088
0.1629


8
0.1298
0.1662





TKN in g nitrogen/100 g liquid sample













TABLE 96







Percentage conversion of the total TKN to soluble TKN for


Experiment 1 (cow hair)










Air-dried hair




concentration









Time (h)
40 g/L
60 g/L












0
2.72
3.70


0.5
3.14
5.62


1
7.38
7.91


2
12.19
11.31


3
12.80
13.51


4
14.73
15.48


6
18.47
18.43


8
22.03
18.81









FIG. 38 presents the protein solubilization (percentage conversion) as a function of time for the different hair concentrations studied. It shows that hair concentration has no important effect on protein hydrolysis (conversion) and that higher lime loadings or a longer treatment period are required to obtain conversions on the order of 70%, which can be obtained with chicken feathers, another keratin material.
As Table 94 shows, the dissolved solids are higher for the higher hair concentration, as expected. The final pH for both cases is lower than the initial 12.0, implying that lime was consumed during the hydrolysis and that lime was not present as a solid in the final mixture.
Experiment 2
Lime Loading Effect
To determine the effect of lime loading on protein solubilization of air-dried hair, experiments were run at different lime/hair ratios keeping the temperature and hair concentration constant (100° C. and 40 g air-dried hair/L, respectively). The experimental conditions studied and variables measured are summarized in Table 97.







TABLE 97







Experimental conditions and variables measured to determine


the lime loading effect in protein solubilization of cow hair









Lime loading (g lime/g hair)












0.10
0.20
0.25
0.35















Mass of hair (g)
34
34
34
34


Volume of water (mL)
850
850
850
850


Mass of lime (g)
3.4
6.8
8.5
11.9


Temperature (° C.)
100
100
100
100


Initial temperature (° C.)
101.4
102.3
75.6
90.2


pH final
9.2
10.3
11.4
11.2


Residual solid (g)
28.8
17.44(*)
22.6
22.9


Dissolved solids in 100 mL (g)
1.18
2.92(*)
2.96
2.99


Protein in 100 mL (g)
0.81
1.77
2.18
2.40





(*)Measured after 48 h and not at 8 h as the other three conditions.






Table 98 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different lime loadings. On the basis of the average TKN for air-dried hair (14.73%), the protein hydrolysis conversions are estimated and given in Table 99.







TABLE 98







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 2 (cow hair)










Lime loading












Time (min)
0.10 g/g
0.20 g/g
0.25 g/g
0.35 g/g
















0
0.0160
0.0144
0.0241
0.0133



0.5
0.0185
—
0.0454
0.0637



1
0.0435
0.0845
0.0922
0.0822



2
0.0718
0.1425
0.1350
0.1438



3
0.0754
—
0.1549
0.1792



4
0.0868
0.2145
0.1951
0.2023



6
0.1088
—
0.2699
0.2999



8
0.1298
0.2832
0.3487
0.3837







TKN in g nitrogen/100 g liquid sample.













TABLE 99







Percentage conversion of the total TKN to soluble TKN for


Experiment 2 (cow hair)










Lime loading












Time (min)
0.10 g/g
0.20 g/g
0.25 g/g
0.35 g/g














0
2.72
 2.44
4.09
2.26


0.5
3.14
—
7.71
10.81


1
7.38
14.34
15.65
13.95


2
12.19
24.19
22.91
24.41


3
12.80
—
26.29
30.41


4
14.73
36.41
33.11
34.33


6
18.47
—
45.81
50.90


8
22.03
48.07
59.18
65.12









FIG. 39 presents the protein solubilized (percentage conversion) as a function of time for the different lime loadings studied. It shows that the conversion is similar for all lime loadings, except for 0.1 g lime/g air-dried hair. FIG. 38 shows that the conversions differ more at longer times and that the reaction does not slow down at 8 h for any of the lime loading studied. Hence, a longer treatment period may increase the conversion and the minimum lime loading required for the process to be efficient.
As Table 97 shows, the dissolved solids are higher for the higher lime loadings as expected (higher calcium salts in solutions and higher conversion). The final pH increases the lime loading increases, and is lower than 12.0 in all cases, again implying the consumption of lime during the hydrolysis and that the final OH-concentration (pH) can be related back to the efficiency of the treatment.
The behavior shown in FIG. 39 can be related to the requirement for the hydroxyl group as a catalyst for the hydrolysis reaction. The low solubility of lime maintains a “constant” lime concentration in all treatments (0.2 to 0.35 g lime/g air-dried hair), but its consumption during the process makes the lower lime loading reaction slow down or level off faster.
Experiment 3
Effect of Longer Term Treatment
To establish the effect of a long-term treatment in the solubilization of protein, experiments were run at two different conditions: 100° C., 0.2 g lime/g air-dried hair with 40 g air-dried hair/L; and 100° C., 0.35 g lime/g air-dried hair with 40 g air-dried hair/L, respectively. The experimental conditions studied and variables measured are summarized in Table 100.







TABLE 100







Experimental conditions and variables measured for


determining the effect of a longer treatment period in


protein solubilization of cow hair










Lime loading




(g lime/g air-dried hair)












0.2
0.35















Mass of hair (g)
34
34



Volume of water (mL)
850
850



Mass of lime (g)
6.8
11.9



Temperature (° C.)
100
100



pH final
10.3
11.99



Residual solid (g)
17.44
10.74



Dissolved solids in 100 mL (g)
2.92
4.01



Protein in 100 mL (g) at 48 h
2.25
2.63










Table 101 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different lime loadings. On the basis of the average TKN for air-dried hair (14.73%), the protein hydrolysis conversions are estimated and given in Table 102.







TABLE 101







Total Kjeldhal nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 3 (cow hair)










Lime loading










Time (h)
0.20 g/g
0.35 g/g












0
0.0144
0.0133


1
0.0845
—


2
0.1425
—


4
0.2145
0.2088


8
0.2832
0.2832


12
0.3089
—


24
0.3319
0.3988


36
0.3617
0.4265


48
0.3597
0.4210





TKN in g nitrogen/100 g liquid sample.













TABLE 102







Percentage conversion of total TKN to soluble TKN for Experiment 3


(cow hair)










Lime loading










Time (h)
0.20 g/g
0.35 g/g












0
2.44
 2.26


1
14.34
—


2
24.19
—


4
36.41
35.44


8
48.07
48.07


12
52.43
—


24
56.33
67.68


36
61.39
72.39


48
61.05
71.45









FIG. 40 presents the protein solubilization (percentage conversion) as a function of time for the two different conditions studied. It shows that the conversions differ for the longer time treatments and that the reaction reaches the highest conversion between 24 and 36 hours of treatment. The relation between lime availability and conversion is more perceptible in this long-term treatment study.
There is a very perceptible ammonia odor, starting at 24 hours, that suggests amino acid degradation at longer periods. One way to reduce this problem is to recover amino acids already hydrolyzed to the liquid phase with separation of residual solids for further alkaline hydrolysis in subsequent treatment steps.
Experiment 4
Ammonia Measurements During Alkaline Hydrolysis of Air-Dried Cow Hair (Amino Acid Degradation)
The effect of a long-term treatment in the solubilization of protein and the degradation of soluble amino acids was determined by ammonia measurements. The ammonia concentration was determined as a function of time for the two experimental conditions of Experiment 3 and for an additional run that used the centrifuged liquid of an experiment performed at 100° C., 0.2 g lime/g air-dried hair with 40 g air-dried hair/L for 5 hours. The experimental conditions studied and variables measured are summarized in Table 103.







TABLE 103







Experimental conditions and variables measured for determining


the effect of a longer treatment period on amino acid degradation









Lime loading (g lime/g air-dried hair)











0.2
0.35
0.35



(Exp. A1)
(Exp. A2)
(Exp. A3)














Mass of hair (g)
34
34
**


Volume of water (mL)
850
850
850


Mass of lime (g)
6.8
11.9
8.5


Temperature (° C.)
100
100
100


Initial temperature (° C.)
102.3
98.8
96.6


pH final
10.3
11.99
12.08


Residual solid (g)
17.44
10.74
8.28


Dissolved solids in 100 mL (g)
2.92
4.01
2.50


Protein in 100 mL (g) at 48 h
2.25
2.63
1.41





** No solid material was used, only the centrifuged liquid from a previous experiment.






Tables 104-106 and FIGS. 41-43 show the total nitrogen content and the free ammonia concentration in the centrifuged liquid samples as a function of time for the different experimental conditions.







TABLE 104







Total Kjeldhal nitrogen content, ammonia concentration and


estimated protein nitrogen in the centrifuged liquid phase as


a function of time for Experiment A1 (cow hair)












[Ammonia]
TKN
TKN
Protein-N


Time (h)
(ppm)
(%)
(ppm)
(ppm)














0
34
0.0144
144
110


1
33
0.0845
845
812


2
41
0.1425
1425
1384


4
76
0.2145
2145
2069


8
175
0.2832
2832
2657


12
236
0.3089
3089
2853


24
274
0.3319
3319
3045


36
327
0.3617
3617
3290


48
316
0.3597
3597
3281





TKN in g nitrogen/100 g liquid sample.













TABLE 105







Total Kjeldhal nitrogen content, ammonia concentration and


estimated protein nitrogen in the centrifuged liquid phase as


a function of time for Experiment A2 (cow hair)












[Ammonia]
TKN
TKN
Protein-N


Time (h)
(ppm)
(%)
(ppm)
(ppm)














0
0
0
0
0


4
85
0.2088
2088
2003


8
115
0.2832
2832
2717


24
111
0.3988
3988
3877


36
141
0.4265
4265
4124


48
110
0.4210
4210
4100





TKN in g nitrogen/100 g liquid sample.













TABLE 106







Total Kjeldhal nitrogen content, ammonia concentration and


estimated protein nitrogen in the centrifuged liquid phase as


a function of time for Experiment A3 (cow hair)












[Ammonia]
TKN
TKN
Protein-N


Time (h)
(ppm)
(%)
(ppm)
(PPM)














0
50
0.2332
2332
2282


1
50
0.2426
2426
2376


2
51
0.2449
2449
2398


4
60
0.2449
2449
2389


8
90
0.2382
2382
2292


12
106
0.2393
2393
2287


24
86
0.2326
2326
2240


48
87
0.2248
2248
2161





Ammonia concentration in the centrifuged liquid is determined by the Kjeldhal method but with no initial hydrolysis of the sample.


TKN in g nitrogen/100 g liquid sample.






FIGS. 41 and 42 show that the total protein-N concentration increases as a function of time until it reaches a maximum between 24 and 36 h of treatment. The free ammonia concentration also increases as a function of time, suggesting the degradation of amino acids. In Experiments A1 and A2, further hydrolysis of hair into the liquid exceeds amino acid degradation, giving a net improvement of protein-N until the 24-36 h period.
In Experiment A3 no solid hair was present, so there is no protein source other than previously solubilized protein. In this case, the reduction of protein-N occurred after 4 h and continued at 48 h, implying that there are several amino acids that are susceptible to degradation at the conditions studied.
Experiment 4A
Amino Acid Degradation Study
For Experiments A2 and A3, the amino acid composition of liquid samples was analyzed to determine the stability of individual amino acids in the protein hydrolyzate.
Two different amino acid analyses of lime-hydrolyzed cow-hair were performed:

    
    
        1) Free amino acids in the centrifuged liquid. The analysis was made without extra HCL hydrolysis of the sample. No amino acids were destroyed by the analytical procedure, but soluble polypeptides are missing in the analysis.
        2) Total amino acids in the centrifuged liquid.
    
    


HCL hydrolysis was performed before HPLC determination. Some amino acids (asparagine, glutamine, cysteine, and tryptophan) were destroyed by the acid and could not be measured.
Table 107 and Table 108 compare the total amino acids (HCL hydrolysis), the free amino acids, and the estimated amino acids using TKN values. These tables show that hair protein is hydrolyzed mainly to small soluble peptides instead of free amino acids (comparing the free amino acids with the total amino acids columns).







TABLE 107







Protein concentrations comparison for Experiment A2 (cow hair)











Time
TKN
Protein
Free AA
Total AA


(h)
(%)
(mg/L)
(mq/L)
(mg/L)














4
0.2088
13050.0
330.4
4783.5


8
0.2832
17700.0
684.5
9300.4


24
0.3988
24925.0
1454.9
12208.4


36
0.4265
26656.3
1699.2
13680.1


48
0.4210
26312.5
1742.6
13989.6
















TABLE 108







Protein concentrations comparison for Experiment A3 (cow hair)












TKN
Protein
Free AA
Total AA


Time (h)
(%)
(mg/L)
(mg/L)
(mg/L)














0
0.2332
14575.0
413.6
7373.0


1
0.2426
15162.5
816.6
9490.6


2
0.2449
15306.3
989.4
11075.4


4
0.2449
15306.3
1154.7
12040.4


8
0.2382
14887.5
1393.9
10549.1


12
0.2393
14956.3
1571.9
9988.4


24
0.2326
14537.5
2266.9
8464.8


48
0.2248
14050.0
2236.9
8782.3









Table 108 also shows an increase in the total amino acid concentration between 0 and 4 h. Because this experiment (A3) was performed only with centrifuged liquid (no solid hair), the increasing value can be explained by the presence of suspended polypeptides particles in solution that are further hydrolyzed in the liquid. Liquid was centrifuged at 3500 rpm in the solid separation, whereas 15000 rpm is used before HPLC analysis.
Table 108 shows a very good agreement between the estimated protein (TKN) and the total amino acids concentration at 4 h. At this time, there is relatively little amino acid degradation and a very high conversion of the “suspended material” in the liquid phase. In Table 107, the difference can be explained by the presence of this suspended material, which is not accounted for in the amino acid analysis.
For Experiment A2, FIG. 44 shows the concentration of individual free amino acids present in the centrifuged liquid as a function of time, whereas FIG. 45 shows the total concentration of individual amino acids as a function of time. Histidine concentrations could not be measured or are underestimated because it eluted right before a very high concentration of glycine; hence, the peaks could not be separated.
FIG. 45 shows an increase in all amino acids concentration until 36 h, except for arginine, threonine, and serine. FIG. 44 shows a similar behavior, except that the concentrations are lower, especially for arginine and threonine. At 36 hours the amino acid concentrations level off (except for arginine, threonine, and serine), suggesting equilibrium between the solubilization and degradation processes.
For Experiment A3 (no solid hair added, only centrifuged liquid), FIG. 45 shows the concentration of individual free amino acids present in the centrifuged liquid as a function of time, whereas FIG. 46 shows the total concentration of individual amino acids as a function of time.
In FIG. 46, the concentration of free amino acids increases until 24 h when it levels off. Again, the exceptions are arginine, threonine, and serine, with very low concentrations of the first two as free amino acids.
FIG. 47 shows an increase in all individual amino acids concentration between 0 and 4 h. This implies again the presence of suspended particles in the initial centrifuged liquid that are hydrolyzed to the liquid phase between 0 and 4 h. After this initial trend, the concentrations of all amino acids decline with time, suggesting the degradation of all amino acids under the condition studied for the long-term treatments. Arginine (16% of the concentration obtained at 4 h is present at 48 h), threonine (31%), and serine (31%) degrade more than the other amino acids.
Increasing concentrations of ornithine and citrulline, both not present in perceptible amounts in hair, suggest them as possible degradation products.
Table 109 shows the weight percentage of each amino acid as a function of time for Experiment A2. Similar contents are present for most of the amino acids with the exception of arginine, threonine, and serine. Some amino acid percentages Increase because of their higher resistance to degradation and the decrease of others.







TABLE 109







Individual amino acid present in Experiment A2 as a function of time


compared to the initial material











Amino
Time (h)
















Acid
4
8
24
36
48
Hair



















ASP
6.76
6.90
7.03
6.96
6.77
6.63



GLU
13.31
14.64
15.96
16.42
16.37
14.47



SER
6.68
3.76
1.53
1.11
1.00
8.91



HIS
1.11
0.00
0.00
0.00
0.00
1.29



GLY
9.33
9.48
8.50
8.25
8.29
5.52



THR
2.40
1.66
0.85
0.66
0.54
7.48



CIT
0.91
0.95
1.56
1.68
1.68
0.00



ALA
5.40
6.50
8.63
9.47
9.27
4.50



ARG
9.22
7.79
4.38
2.89
2.11
10.98



TYR
5.35
5.43
5.78
5.87
5.74
2.44



VAL
6.74
7.13
7.45
7.40
7.25
6.80



MET
0.80
0.90
1.05
1.00
1.09
0.71



PHE
3.17
3.05
3.13
3.17
3.15
3.09



ILE
4.04
4.19
4.52
4.62
4.55
4.20



LEU
8.81
9.66
10.92
11.21
11.25
9.77



LYS
2.09
2.71
3.89
4.08
4.14
5.53



PRO
13.77
15.07
14.60
15.02
16.60
7.68







Values in g AA/100 g total amino acids.






Experiment 5
Two-Step Treatment of Material
The amino acid degradation observed in the previous experiments affects the overall efficiency of the hydrolysis process. One way to tackle this problem is to separate the already-hydrolyzed protein with subsequent solubilization of protein (residual solids) in a series of treatment steps. In this experiment, two conditions were studied to determine the effect of a two-step process in the hydrolysis efficiency and the amino acid degradation of protein in air-dried hair. The experimental conditions studied and variables measured are summarized in Table 110.







TABLE 110







Experimental conditions and variables measured to


determine the lime loading effect in protein solubilization


(cow hair - two step treatment)









Experiment












Exp. C1
Exp. C2
Exp. D1
Exp. D2















Mass of hair (g)
34
20
34
20


Volume of water (mL)
850
850
850
850


Mass of lime (g)
8.5
5
11.9
5


Temperature (° C.)
100
100
100
100


Initial temperature (° C.)
75.6
96.5
90.2
105


pH final
11.4
11.2
11.2
11.2


Residual solid (g) at 8 h
22.6
12.7
22.9
12.4


Dissolved solids in 100 mL (g)
2.96
1.15
2.99
1.17


Protein in 100 mL (g) at 8 h
1.80
0.91
1.78
0.86









Table 111 shows the total nitrogen content in the centrifuged liquid sample as a function of time for the different experimental conditions. On the basis of the average TKN for air-dried hair (14.73%), the protein hydrolysis conversions were estimated and given in Table 112. FIG. 48 shows the total conversion for the process (Step 1+Step 2) as a function of time.







TABLE 111







Total Kjeldhal nitrogen content in the centrifuged liquid


phase as a function of time for Experiment 5 (cow hair)











Time (h)
Exp. C1
Exp. C2
Exp. D1
Exp. D2














0
0.0241
0.0363
0.0133
0.0365


0.5
0.0454
0.0553
0.0637
0.0481


1
0.0922
0.0560
0.0822
0.0571


2
0.1350
0.0620
0.1438
0.0631


3
0.1549
0.0756
0.1792
0.0704


4
0.1951
0.0745
0.2023
0.0798


6
0.2299
0.1135
0.2269
0.1042


8
0.2887
0.1450
0.2837
0.1383





TKN in g nitrogen/100 g liquid sample.













TABLE 112







Percentage conversion of the total TKN to


soluble TKN for Experiment 5 (cow hair)











Time (h)
Exp. C1
Exp. C2
Exp. D1
Exp. D2














0
4.09
6.16
2.26
6.19


0.5
7.71
9.39
10.81
8.16


1
15.65
9.50
13.95
9.69


2
22.91
10.52
24.41
10.71


3
26.29
12.83
30.41
11.95


4
33.11
12.64
34.33
18.54


6
39.02
19.26
38.51
17.68


8
49.00
24.61
48.15
23.47









FIG. 48 shows a similar conversion for the two conditions studied. At 16 h of treatment, a total of 70% of the initial nitrogen is recovered in the liquid phase. The total conversion increases during the second treatment and a lower concentration of ammonia is present compared to the one-step treatment (Table 113), which suggest a lower degradation of amino acids. Hence, further treatment of the residual solid with lime hydrolyzes more hair, but the concentration of nitrogen (protein/amino acids) in the second step is only 40% of the obtained in the initial treatment, which increases the energy required for water evaporation. Because the initial concentration of hair has no important effect in the conversion, a higher product concentration might be obtained with a semi-solid reaction.







TABLE 113







Total Kjeldhal nitrogen and ammonia concentration


for the two-step and the one-step process













Step 1 (8 h)
Step 2 (8 h)
One-Step (16 h)
















TKN
0.2984
0.1154
0.3525



Ammonia
87
39
363










The separation of the initial liquid at 8 h ensures relatively high concentrations for the susceptible amino acids (arginine, threonine, and serine) with approximately 50% conversion of the initial protein. The second step gives a higher total conversion with lower concentrations of these amino acids.
The unreacted residual solid after Step 2 (approximately 30% of the initial hair with 7 g nitrogen/100 g dry solid) could be further treated to give a total of 80% protein recovery in the liquid phase. This step will probably require between 24 and 36 hours.
Experiment 6
Amino Acid Composition of Products and Process Mass Balance
This section presents the total mass balance and the amino acid composition of the products obtained with the suggested two 8-h step process and the one 16-h step treatment.
Table 113 compares the total Kjeldhal nitrogen and the ammonia concentration for the three centrifuged liquid products. Table 114 shows the solid composition (nitrogen and minerals) for the three residual solids. FIG. 49 shows the mass balance for the two-step process and the one-step process. Non-homogeneity in solids produces very high variation in concentrations.







TABLE 114







Protein and mineral content of air-dried hair and residual solids of the process


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















Hair
14.73
0.0508
0.0197
0.1658
0.029
5244
58
185
50
37


 RS1 8 h
10.234
0.0622
0.0176
7.0083
0.1233
3005
108
457
61
17


 RS2 8 h
6.974
0.0725
0.0155
10.1003
0.1938
2301
117
702
62
22


RS3 16 h
5.803
0.0642
0.0228
9.7181
0.1617
2404
79
472
56
18









Table 115 compares the amino acid composition for the three different products and the hair. As expected from previous experiments, Step 1 gives the higher values for threonine, arginine, and serine. With the exception of the previously mentioned amino acids, the concentration of the product from Step I, Step 2, and the one-step process are very similar.







TABLE 115







Individual amino acid present in solid products and the starting material











Amino acid
Step 1 (8 h)
Step 2 (8 h)
One-Step (16 h)
Hair














ASP
8.19
8.68
7.85
6.63


GLU
17.46
19.30
17.51
14.47


SER
3.01
1.10
1.57
8.91


HIS
1.06
0.83
0.94
1.29


GLY
10.00
6.97
9.84
5.52


THR
1.32
0.83
0.76
7.48


ALA
7.34
7.80
8.64
4.50


ARG
7.95
4.94
5.25
10.98


TYR
1.75
2.14
2.59
2.44


VAL
7.82
8.99
8.20
6.80


MET
0.73
0.99
0.75
0.71


PHE
3.37
3.39
3.38
3.09


ILE
4.62
5.21
4.82
4.20


LEU
11.01
13.04
11.52
9.77


LYS
2.77
4.82
3.91
5.53


PRO
11.62
10.94
12.45
7.68





Values in g AA/100 g total amino acids.






Finally, in Table 116, the amino acid composition of the products was compared to the needed essential amino acids of various monogastric domestic animals.








TABLE 116







Amino acid analysis of product and essential amino acids requirements


for various domestic animals
















Amino
Step 1
Step 2
One-Step








Acid
(8 h)
(8 h)
16 h
Hair
Catfish
Dogs
Cats
Chickens
Pigs



















ASP
8.19
8.68
7.85
6.63







GLU
17.46
19.30
17.51
14.47


SER
3.01
1.10
1.57
8.91


HIS
1.06
0.83
0.94
1.29
1.31
1
1.03
1.4
1.25


GLY
10.00
6.97
9.84
5.52


THR
1.32
0.83
0.76
7.48
1.75
2.64
2.43
3.5
2.5


ALA
7.34
7.80
8.64
4.50


ARG
7.95
4.94
5.25
10.98
3.75
2.82
4.17
5.5
0


VAL
7.82
8.99
8.20
6.80
2.63
2.18
2.07
4.15
2.67


CYS
ND
ND
ND
ND
2+  
2.41+
3.67+
4+  
1.92+


MET
0.73
0.99
0.75
0.71
2+  
2.41+
2.07
2.25
1.92+


TYR
1.75
2.14
2.59
2.44
 4.38*
4.05*
2.93*
 5.85*
3.75*


PHE
3.37
3.39
3.38
3.09
 4.38*
4.05*
1.4
3.15
3.75*


ILE
4.62
5.21
4.82
4.20
2.28
2.05
1.73
3.65
2.5


LEU
11.01
13.04
11.52
9.77
3.06
3.27
4.17
5.25
2.5


LYS
2.77
4.82
3.91
5.53
4.47
3.5
4
5.75
3.58


TRP
ND
ND
ND
ND
0.44
0.91
0.83
1.05
0.75


PRO
11.62
10.94
12.45
7.68





+Cysteine + methionine


*Tyrosine + phenylalanine


ND Not determined


All values are in g amino acid/100 g protein.






As shown in Table 116, the amino acid composition of lime-hydrolyzed cow hair is not well balanced with respect to the essential amino acid requirements of different domestic monogastric animals. There are particularly low values for histidine (underestimated in the analysis), threonine, methionine, and lysine some other amino acids are sufficient for the majority of animals, but not all (tyrosine, phenylalanine). Lime hydrolysis, of cow hair generates a product that is very rich in proline and glutamine+glutamate, but these are not essential amino acids in the diet of domestic monogastric animals. The amino acid product can be used for ruminants.
A higher serine and threonine concentration could be obtained by reducing the time in Step 1.
Air-dried cow hair, containing 92% protein (wet basis), can be used to obtain an amino acid-rich product by treating with Ca(OH)2 at 100° C. A simple non-pressurizing vessel can be used for the above process due to the low temperature requirements.
Hair concentration has no important effect on protein hydrolysis, whereas high lime loadings (greater than 0.1 g Ca(OH)2/g hair) and long treatment periods (t>8 h) are required to obtain conversions of about 70%, which also can be obtained from chicken feathers, another keratin material.
Protein solubilization varies with lime loading only for the long-term treatment, showing that the hydroxyl group is required as a catalyst for the hydrolysis reaction, but its consumption during the process makes the lower lime loading reaction slow down or level off faster.
The optimal conditions to maximize protein conversion (up to 70%) are 0.35 g Ca(OH)2/g air-dried hair processed at 100° C. for at least 24 hours. A very perceptible ammonia odor, starting at 24 hours, suggests amino acid degradation. Arginine, threonine and serine are the more susceptible amino acids under alkaline hydrolysis.
Degradation of amino acids can be minimized by recovering the amino acids already hydrolyzed into the liquid phase, with separation of residual solids for further alkaline hydrolysis in subsequent treatment steps. The separation of the initial liquid (Step 1) at 8 h ensures relatively high concentrations for the susceptible amino acids (arginine, threonine, and serine) with approximately 50% conversion of the initial protein. The second 8-h step gives a higher total conversion (approximately 70%) with lower concentrations of these amino acids.
Nitrogen concentration (protein/amino acids) in Step 2 is only 40% of that obtained in the initial treatment, which increases the energy required for water evaporation. Because the initial concentration of hair has no important effect in the conversion, a higher product concentration might be obtained with a semi-solid reaction.
The amino acid composition of the product compares poorly with the essential amino acid requirements for various domestic monogastric animals. The product is low in threonine, histidine, methionine, and lysine. It is especially rich in asparagine and proline, but these are not required in animal diets. The products obtained by this process are valuable as ruminant feed, have a very high digestibility, a high nitrogen content, and are highly soluble in water.
Example 7
Protein Solubilization in Shrimp Heads
Considerable amounts of shrimp processing by-products are discarded each year. In commercial shrimp processing about 25% (w/w) of the live shrimp is recovered as meat. The solid waste contains about 30-35% tissue protein; calcium carbonate and chitin are the other major fractions. Chitin and chitosan production are currently based on waste from crustacean processing. During chitosan production, for every kg of chitosan produced, about 3 kg of protein are wasted (Gildberg and Stenberg, 2001).
Chitin is a widely distributed, naturally abundant amino polysaccharide, insoluble in water, alkali, and organic solvents, and slightly soluble in strong acids. Chitin is a structural component in crustacean exoskeletons, which are  ̃15-20% chitin by dry weight. Chitin is similar to cellulose both in chemical structure and in biological function as a structural polymer (Kumar, 2000).
At the present time, chitin-containing materials (crab shell, shrimp waste, etc.) are treated in boiling aqueous sodium hydroxide (4% w/w) for 1-3 h followed by decalcification (calcium carbonate elimination) in diluted hydrochloric acid (1-2 N HCL) for 8-10 h. Then chitin is deacetylated to become chitosan in concentrated sodium hydroxide (40-50% w/w) under boiling temperature.
Frozen large whole white shrimps were obtained from the grocery store. Shrimp tails were removed and the residual waste (heads, antennae, etc.) was blended for 10 min in an industrial blender, collected in plastic bottles and finally frozen at −4° C. for later use. Samples of this blended material were used to obtain the moisture content, the total nitrogen (estimate of the protein  ̃16%+chitin fraction  ̃16.4% of total weight is nitrogen), the ash (mineral fraction), and the amino acid content to characterize the starting material.
Shrimp head waste was 21.46% dry material and 17.2 g ash/100 g dry weight (Table 117 and Table 118). The TKN was 10.25% corresponding to a crude protein and chitin fraction of about 64.1% (Table 119). The remaining 18% corresponds to lipids and other components. The amino acid composition for shrimp head waste is given in Table 120.







TABLE 117







Moisture content in shrimp head waste













Solid
Dry Solid
Dry solid



Sample
(g)
(g)
(%)







1
64.1091
13.7745
21.49



2
58.5237
12.5662
21.47



3
61.7193
13.2126
21.41





Mean
21.46

















TABLE 118







Ash content in shrimp head waste













Solid
Dry Solid
Dry solid



Sample
(g)
(g)
(%)
















1
3.2902
0.5859
17.81



2
3.068
0.5148
16.78



3
3.0486
0.5196
17.04





Mean
17.21

















TABLE 119







Protein and mineral content in shrimp head waste


















TKN
P
K
Ca
Mg
Na
Zn
Fe
Cu
Mn


Sample
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)




















1
10.2
1.34
1.07
4.5430
0.3896
12090
90
355
160
10


2
10.3
1.21
1.02
4.7162
0.3586
11550
90
167
155
9


Mean
10.25
1.27
1.045
4.6296
0.3781
11820
90
261
157.5
95
















TABLE 120







Amino acid composition of shrimp head waste












Amino acid
Measured
Amino acid
Measured
















ASP
11.13
TYR
3.15



GLU
15.83
VAL
5.77



SER
4.08
MET
1.84



HIS
1.78
PHE
4.93



GLY
6.94
ILE
4.54



THR
4.06
LIEU
8.30



ALA
6.83
LYS
5.63



OYS
ND
TRIP
ND



ARG
7.25
PRO
7.96







ND: Not determined



Values in g AA/100 g total amino acids.






The starting material contains a well-balanced amino acid content (Table 120); with relatively low levels of histidine and methionine. High levels of phosphorous, calcium, potassium make the material a valuable source for minerals in animal diets.
Experiment 1
Repeatability
To determine the repeatability of the solubilization process of protein in shrimp head waste, two experiments were run under the same conditions (100° C., 40 g dry shrimp/L, and 0.10 g lime/g dry shrimp respectively). The experimental conditions and variables measured are summarized in Table 121.







TABLE 121







Experimental conditions and variables measured for determining the


repeatability in protein solubilization of shrimp head waste











Experiment
A
B















Mass of shrimp head waste (g)
149
149



Volume of water (mL)
750
750



Mass of lime (g)
3.2
3.2



Initial temperature (° C.)
97
87



pH final
10.64
10.2



Humid residual solid (g)
137.19
182.7



Dry residual solid (g)
17.24
19.74



Dissolved solids in 100 mL (g)
2.3757
2.4322










Table 22 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the two different runs. On the basis of the average TKN for dry shrimp head wastes (10.25%), the protein hydrolysis conversions were estimated and given in Table 123. The average standard deviation for the conversion values is 1.13 or 1.5% of the average result (79.3% conversion).







TABLE 122







Total Kjeldhal nitrogen content in the centrifuged liquid phase as a


function of time for Experiment 1 (shrimp head waste)









Time (min)
A
B












0
0.2837
0.2934


10
0.3005
0.3017


20
0.3053
0.2981


30
0.3029
0.3005


60
0.3053
0.2969


120
0.3077
0.3005





TKN in g nitrogen/100 g liquid sample.













TABLE 123







Percentage conversion of the total TKN to soluble TKN for Experiment 1


(shrimp head waste)









Time (min)
A
B












0
75.1
77.6


10
79.5
79.8


20
80.8
78.9


30
80.1
79.5


60
80.8
78.6


120
81.4
79.5









FIG. 49 presents the protein solubilization (percentage conversion) as a function of time for the two different runs. It shows that the conversion remains constant after the initial 5-10 min, and that the protein hydrolysis process is fairly repeatable under the conditions studied. For the sample for time 0 min, is taken after the reactor is closed and pressurized, this process takes between 8 and 12 min.
Experiment 2
Temperature Effect
To determine the effect of temperature on solubilizing protein in shrimp head waste, experiments were run at different temperatures keeping the lime loading and material concentration constant (0.10 g lime/g shrimp and 40 g dry shrimp/L respectively). The experimental conditions and variables measured are summarized in Table 124.







TABLE 124







Experimental conditions and variables measured to determine the effect


of temperature in protein solubilization of shrimp head waste









Temperature (° C.)











75
100
125














Mass of shrimp (g)
149
149
149


Volume of water (mL)
750
750
750


Mass of lime (g)
3.2
3.2
3.2


Initial temperature (° C.)
78.5
97
108


pH final
10.1
10.64
9.88


Humid residual solid (g)
133.04
137.19
130.58


Dry residual solid (g)
16.06
17.24
17.42


Dissolved solids in 100 mL (g)
2.6439
2.3757
2.6808









Table 125 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different temperatures. On the basis of the average TKN for dry shrimp head waste (10.25%), the protein hydrolysis conversions were estimated and given in Table 126.







TABLE 125







Total Kjeldhal nitrogen content in the centrifuged liquid phase as a


function of time for Experiment 2 (shrimp head waste)









Temperature












Time (min)
75° C.
100° C.
125° C.
















0
0.3160
0.2837
0.3053



10
0.3196
0.3005
0.3101



20
0.3101
0.3053
0.3101



30
0.3101
0.3029
0.3112



60
0.3101
0.3053
0.3101



120
0.3172
0.3077
0.3101







TKN in g nitrogen/100 g liquid sample.













TABLE 126







Percentage conversion of the total TKN to soluble TKN for Experiment 2


(shrimp head waste)









Temperature












Time (min)
75° C.
100° C.
125° C.
















0
83.6
75.1
80.8



10
84.6
79.5
82.1



20
82.1
80.8
82.1



30
82.1
80.1
82.3



60
82.1
80.8
82.1



120
83.9
81.4
82.1










FIG. 51 presents the protein hydrolysis (percentage conversion) as a function of time for the different temperatures studied. The conversion does not depend on temperature (statistically the same value). The lower temperature is favored because the amino acids Should degrade less, and the energy required to keep the process at this temperature is also less.
Experiment 3
Lime Loading Effect I
To determine the effect of lime loading on protein solubilization of shrimp head waste, experiments were run at different lime/shrimp ratios keeping the temperature and shrimp concentration constant (100° C. and 40 g dry shrimp/L respectively). The experimental conditions and variables measured are summarized in Table 127.







TABLE 127







Experimental conditions and variables measured to determine the lime


loading effect in protein solubilization of shrimp head waste









Lime loading (g lime/g shrimp)












0
0.05
0.1
0.2















Mass of shrimp head
149
149
149
149


waste (g)


Volume of water (mL)
750
750
750
750


Mass of lime (g)
0
1.6
3.2
6.4


Initial Temperature
96
95
97
103


(° C.)


pH final
8.1
9.20
10.64
12


Humid residual solid (g)
179.4
148.8
137.2
122.5


Dry residual solid (g)
17.72
16.5
17.24
18.28


Dissolved solids in
2.3576
2.5146
2.3757
2.4516


100 mL (g)









Table 128 shows the total nitrogen content in the centrifuged liquid samples as a function of time for the different lime loadings. On the basis of the average TKN for dry shrimp head waste (10.25%), the protein hydrolysis conversions were estimated (Table 129).







TABLE 128







Total Kjerahl nitrogen content in the centrifuged liquid phase


as a function of time for Experiment 3 (shrimp head waste)










Lime loading












Time (min)
0 g/g
0.05 g/g
0.1 g/g
0.2 g/g














0
0.2477
0.2890
0.2837
0.2573


10
0.2452
0.2978
0.3005
0.2573


20
0.244
0.3035
0.3053
0.2621


30
0.2488
0.3035
0.3029
0.2669


60
0.2452
0.3051
0.3053
0.2766


120
0.2513
0.3035
0.3077
0.2897





TKN in g nitrogen/100 g liquid sample.













TABLE 129







Percentage conversion of the total TKN to soluble


TKN for Experiment 3 (shrimp head waste)










Lime loading












Time (min)
0 g/g
0.05 g/g
0.1 g/g
0.2 g/g














0
65.5
76.5
76.4
68.1


10
64.9
78.8
79.7
68.1


20
64.6
80.3
79.8
69.4


30
65.8
80.3
79.8
70.6


60
64.9
80.7
79.7
73.2


120
66.5
80.3
80.5
76.7









FIG. 52 presents the protein solubilized (percentage conversion) as a function of time for the different lime loadings studied. It shows that the conversion is similar for all lime loadings, except for the experiment with no lime (statistically different).
In the no-lime experiment, there is soluble protein present in the water phase; however, hydroxyl groups are dilute, making the hydrolysis reaction and cell breakage slow-down. The final pH for the no-lime experiment was 8.1. Likely, the alkaline pH is caused by the calcium carbonate and bicarbonate released from the shrimp waste.
The addition of lime is required to ensure fast protein hydrolysis into the liquid phase, and would likely give a higher fraction of free amino acids in the product. Also, because the lime treatment is considered as a preliminary step for generating chitin and chitosan, a high protein recovery is related to reducing chemicals required for subsequent steps during processing, and a higher quality chitin or chitosan product.
The recovery of carotenoids (astaxanthin) from the suspended solids could be considered for generating an additional valuable product from the process. Because calcium carbonate and chitin are structural components in the crustacean, straining the mixture and centrifuging the suspended solids could recover carotenoids (Gildberg and Stenberg, 2001).
Experiment 4
Amino Acid Analysis
Table 130 shows the total amino acid composition of the hydrolyzate for different process conditions. With the exception of serine and threonine in the high-lime-loading experiment, and a relatively high variation in the cysteine content, the composition of the final product does not vary with the treatment conditions. As shown in previous results, the no-lime experiment produces a lower protein concentration in the hydrolyzate.







TABLE 130







Total amino acid composition with different process conditions protein


hydrolysis of shrimp head waste














100° C.
100° C.
100° C.
100° C.
75° C.
125° C.



60 min
120 min
120 min
120 min
120 min
120 min


Conditions
0.1 lime
0.2 lime
0.1 lime
No lime
0.1 lime
0.1 lime
















ASP
9.66
10.19
9.27
9.78
9.46
9.40


GLU
15.68
15.85
15.50
15.68
15.03
15.20


SER
4.57
3.92*
4.33
4.46
4.41
4.38


HIS
0.00
0.00
0.00
0.00
0.00
0.00


GLY
7.77
8.31
7.32
7.26
7.05
7.42


THR
3.57
2.30*
4.01
4.46
4.40
3.77


ALA
7.15
7.53
7.28
7.20
6.69
7.17


TAU
0.00
0.00
0.00
0.00
0.00
0.00


ARG
7.00
6.47
7.59
4.90*
7.94
6.60


TYR
3.82
4.27
3.78
3.94
3.83
4.13


CYS—CYS
0.67
0.48
0.82
1.42
1.09
0.74


VAL
5.79
6.13
6.08
6.17
6.24
6.30


MET
2.19
2.15
2.21
2.25
2.15
2.14


TRP
ND
ND
ND
ND
ND
ND


PHE
4.43
4.90
4.43
4.67
4.57
4.81


ILE
4.01
4.32
4.31
4.30
4.33
4.51


LEU
8.60
8.94
8.75
9.02
8.83
8.97


LYS
7.79
7.31
7.34
7.52
7.53
7.59


PRO
7.30
6.92
6.97
6.97
6.45
6.85





ND: Not determined


Values in g AA/100 g total amino acids.






Table 131 shows the free amino acid composition of the hydrolyzate for different process conditions. The composition variability is higher than in the total amino acids case. Treatment conditions affect susceptible amino acids; stronger conditions (e.g., longer times, higher temperatures, or higher lime loadings) accelerate the degradation reactions and generate different compositions, especially in the free amino acid determination.
Tryptophan represents approximately 2% of the free amino acid composition, whereas taurine is close to 4%. These values can be used as estimates for their concentrations in the total amino acid composition.







TABLE 131







Free amino acid composition with different process conditions for


protein hydrolysis of shrimp head waste














100° C.
100° C.
100° C.
100° C.
75° C.
125° C.



60 min
120 min
120 min
120 min
120 min
120 min


Conditions
0.1 lime
0.2 lime
0.1 lime
No lime
0.1 lime
0.1 lime
















ASP
1.61
3.85
2.09
2.93
216
2.75


GLU
3.49
5.54
3.86
4.46
4.08
4.20


ASN
1.87
0.83
2.15
2.40
2.53
2.12


SER
3.01
4.15
3.17
3.37
3.20
3.59


GLN
1.67
0.00
2.05
2.69
3.29
0.18


HIS
0.00
0.00
0.00
0.00
0.00
0.00


GLY
8.51
8.61
6.55
6.54
5.80
6.59


THR
2.44
1.38
3.00
3.38
3.25
2.91


CIT
0.52
1.13
0.58
0.38
0.67
0.36


B-ALA
0.50
0.25
0.09
0.02
0.00
0.15


ALA
8.71
9.21
8.41
8.45
7.85
8.98


TAU
6.51
5.63
4.31
3.84
3.48
3.95


ARG
11.45
9.37
11.63
6.53
11.46
9.51


TYR
3.93
4.35
4.72
5.40
5.06
5.25


CYS—CYS
ND
ND
ND
ND
ND
ND


VAL
4.10
4.61
4.84
4.87
4.85
5.50


MET
2.78
3.22
3.22
3.36
3.01
2.89


TRP
2.78
2.57
2.32
2.17
2.16
1.86


PHE
4.55
4.74
5.17
6.15
5.87
5.56


ILE
3.86
3.92
4.82
4.32
4.45
5.72


LEU
7.63
8.15
8.90
9.82
9.60
9.75


LYS
10.31
9.39
9.82
10.98
9.32
9.82


PRO
9.78
9.10
8.28
7.95
7.91
8.37





ND: Not determined


Valves in g AA/100 g total free amino acids.






An average of 40% of the total amino acids is present as free amino acids. A relatively higher fraction is obtained for longer times or stronger conditions.
The thermo-chemical treatment of shrimp waste produces a mixture of free. amino acids and small soluble peptides) making it a potential nutritious product. The hydrolyzate product contains a high :fraction of essential amino acid) making it a high quality nutritional source for monogastric animals. Table 132 shows a comparison between the total amino acid composition and the requirement for various domestic animals. Because histidine is underestimated during the analysis, and using the 1.78 g/100 g value calculated for the raw waste material, a high quality protein supplement is generated that meets or exceed the essential amino acids requirements of the animals during their growth phase.







TABLE 132







Amino acid analysis of product and essential amino acids


requirements for various domestic animals (shrimp head waste)














Amino





Liquid
Liquid


Acid
Catfish
Dogs
Cats
Chickens
Pigs
(TAA)
(FAA)

















ASN






2.15


GLN






2.05


ASP





9.27
2.09


GLU





15.50
3.86


SER





4.33
3.17


HIS
1.31
1.00
1.03
1.40
1.26
0.00
0.00


GLY





7.32
6.55


THR
1.75
2.64
2.43
3.50
2.50
4.01
3.00


ALA





7.28
8.41


ARG
3.75
2.82
4.17
5.50
0.00
7.59
11.63


VAL
2.63
2.18
2.07
4.15
2.67
6.08
4.48


CYS
2.00*
2.41*
3.67*
4.00*
1.92*
0.82
ND


MET
2.00*
2.41*
2.07
2.25
1.92*
2.21
3.22


TYR
4.38+
4.05+
2.93+
5.85+
3.75+
3.78
4.72


PHE
4.38+
4.05+
1.40
3.15
3.75+
4.43
5.17


ILE
2.28
2.05
1.73
3.65
2.50
4.31
4.82


LEU
3.06
3.27
4.17
5.25
2.50
8.75
8.90


LYS
4.47
3.50
4.00
5.75
3.58
7.34
9.92


TRP
0.44
0.91
0.83
1.05
0.75
ND
2.32


PRO





6.97
8.28





*Cysteine + Methionine


+Tyrosine + Phenylalanine


ND Not determined


All values are in g amino acid/100 g protein.






In addition to  ̃20% ash, shrimp head waste contains 64% protein plus chitin, both of which can be used to generate several valuable products. The thermo-chemical treatment of this waste with lime generates a protein-rich material with a well-balanced amino acid content that can be used as an animal feed supplement. Straining the treated mixture and centrifuging the liquid product can recover carotenoids. Finally, the residual solid rich in calcium carbonate and chitin could also be used to generate chitin and chitosan through well-known processes.
For all conditions of temperature, lime loading, and time that were studied, no significant change in conversion occurred after 30 minutes of reaction. Little amino acid degradation was observed for all these conditions and up to 2 h of treatment.
Lime addition is required during the treatment to obtain a higher nitrogen conversion to the liquid phase. This will also reduce the chemicals required for further treatment of the residual solid for chitin and chitosan production.
The product obtained by lime treating the shrimp waste material, meets or exceed the essential amino acid requirements for monogastric animals making it a suitable protein supplement.
Although only exemplary embodiments of the invention are specifically described above, it will be appreciated that modifications and variations of the invention are possible without departing from the spirit and intended scope of the invention.

## Claims

1. A recirculating method of solubilizing protein and destroying prions comprising the following steps in the following order:
first, applying an alkali to an untreated protein source to form a slurry, wherein the alkali is added in an amount sufficient to induce hydrolysis of the protein source when the slurry is heated;
second, heating the slurry to a temperature sufficient to allow hydrolysis of protein in the protein source to obtain a reaction liquid comprising small peptides and free amino acids, and further comprising solid residues;
third, holding the reaction liquid at an elevated temperature between 125-250° C. for a time period sufficient to destroy prions in the reaction liquid;
fourth, separating the solid residues from the reaction liquid;
fifth, neutralizing the reaction liquid with acid or an acid source to produce a neutralized liquid comprising small peptides and free amino acids;
sixth, concentrating the neutralized liquid to produce concentrated liquid comprising small peptides and free amino acids and water; and
seventh, returning the water to the slurry before or during the heating step.

2. The method according to claim 1, further comprising grinding the protein source.

3. The method according to claim 1, wherein the alkali comprises calcium oxide.

4. The method according to claim 1, wherein the alkali comprises a compound selected from the group consisting of: magnesium oxide, magnesium hydroxide, sodium hydroxide, sodium carbonate, potassium hydroxide, ammonia, and any combinations thereof.

5. The method according to claim 1, further comprising neutralizing the ammonia produced during the heating of the slurry with an acid.

6. The method according to claim 1, further comprising separating reactive solid residues from inert solid residues in the separated solid residues.

7. The method according to claim 1, wherein the time period that the reaction liquid is held at an elevated temperature sufficient to destroy prions is between 1 second and 5 hours.

8. The method according to claim 1, further comprising separating solid residues from the neutralized liquid.

9. The method according to claim 1, wherein concentrating the neutralized liquid further comprises evaporating the neutralized liquid.

10. The method according to claim 1, wherein concentrating the neutralized liquid further comprises filtering the neutralized liquid.

11. The method according to claim 1, wherein concentrating the neutralized liquid further comprises freezing the neutralized liquid.

12. The method according to claim 1, wherein concentrating the neutralized liquid further comprises adding an immiscible amine and extracting water using the immiscible ammine.

13. The method according to claim 1, further comprising drying the concentrated liquid.

14. The method according to claim 1, further comprising producing process heat and reusing process heat.

15. The method according to claim 1, wherein the alkali comprises calcium hydroxide.

16. The recirculating method of solubilizing protein comprising the following steps in the following order:
first, applying an alkali to a protein source to form a slurry, wherein the alkali is added in an amount sufficient to induce hydrolysis of the protein source when the slurry is heated;
second, heating the slurry to a temperature sufficient to allow hydrolysis of protein in the protein source to obtain a reaction liquid comprising solid residues;
third, separating the solid residues from the reaction liquid;
fourth, neutralizing the reaction liquid with acid or an acid source to produce a neutralized liquid;
fifth, concentrating the neutralized liquid to produce concentrated liquid and water; and
sixth, returning the water to the slurry before or during the heating step.

17. The method according to claim 16, further comprising grinding the protein source.

18. The method according to claim 16, wherein the alkali comprises calcium oxide.

19. The method according to claim 16, wherein the alkali comprises a compound selected from the group consisting of: magnesium oxide, magnesium hydroxide, sodium hydroxide, sodium carbonate, potassium hydroxide, ammonia, and any combinations thereof.

20. The method according to claim 16, further comprising neutralizing the ammonia produced during the heating of the slurry with an acid.

21. The method according to claim 16, further comprising returning separated solid residues to the protein source.

22. The method according to claim 16, further comprising separating reactive solid residues from inert-solid residues in the separated solid residues.

23. The method according to claim 16, further comprising separating solid residues from the neutralized liquid.

24. The method according to claim 23, wherein the solid residues separated from the neutralized liquid comprise the alkali and further comprising adding the separated solid residues to the protein source.

25. The method according to claim 16, wherein concentrating the neutralized liquid further comprises evaporating the neutralized liquid.

26. The method according to claim 16, wherein concentrating the neutralized liquid further comprises filtering the neutralized liquid.

27. The method according to claim 16, wherein concentrating the neutralized liquid further comprises freezing the neutralized liquid.

28. The method according to claim 16, wherein concentrating the neutralized liquid further comprises adding an immiscible amine and extracting water using the immiscible amine.

29. The method according to claim 16, further comprising drying the concentrated liquid.

30. The method according to claim 16, further comprising producing process heat and reusing process heat.

31. The method according to claim 16, wherein the alkali comprises calcium hydroxide.