Abstract:
Processes for converting by-products of citrus, such as peels and juice from juice sacs attached to the peel after hand or mechanical peeling into high quality dietary fiber, naringin, juice, and oil. The processes involve pressing peels to release juice from vesicles and then grinding peels in water to create a slurry. Peel color and oil is removed by a flotation technique. Decolorized citrus peel particles—or pulp—are debittered with water in steps of boiling and washing. Dietary fiber obtained after debittering is dried and packaged for commercial use. The process promotes environmental responsibility by reducing standard citrus waste—a high BOD waste product, by overcoming discharging problems with industrial waste, by converting an environmentally undesirable product—peels, juice, and oils—into a value-added ingredient, by drastically reducing discharge and penalty cost of waste, and by eliminating the use of solvents that generate pollution.

Description:
FIELD OF THE INVENTION 
     The invention relates to apparatus, systems, and processes for converting citrus peels into fiber, juice, naringin, and oil. 
     BACKGROUND OF THE INVENTION 
     Large scale industrial processing of citrus fruits into juices, canned fruit, fruit salads and other food products generates large volumes of citrus peels as a byproduct. The entire peeling process may be performed manually with specialized knives or mechanically with equipment such as citrus fruit juicers. Many vesicles—juice sacs—are left attached to a citrus peel. Much of citrus mill effluents—peel, rag, seed, pulp, etc.—are dewatered, chopped, kiln dried, or sold as animal feed. It is however well known that citrus peels contain useful and edible components. There is an ongoing commercial interest in identifying uses for left over citrus peels and reducing the environmental impact posed by waste from citrus processing. 
     As people are becoming more health conscious, interest in dietary fiber intake has increased. Dietary fibers from other fiber sources are used more frequently than those from fruit; however, fruit fiber is a high quality dietary fiber. As compared to other forms of fiber, fruit fiber has a higher total and soluble fiber content, water binding capacity, oil absorbing capacity, and colonic fermentability, as well as lower phytic acid content and caloric value. For example, residues from orange juice extraction are recognized as a potentially excellent source of dietary fiber because this material is rich in pectin and is available in large quantities. Citrus-derived fruit fibers are expected to have better quality than other dietary fibers because of the presence of bioactive compounds, such as flavonoids, polyphenols, and carotenes. 
     Intact citrus peels comprise two regions—albedo and flavedo. Albedo is known for its dietary fiber content including sugar, cellulose, and pectic substances. It has been used as a filler material to fortify stock food. Flavedo is known for containing Vitamin A, carotenes, and xanthophylls. It has been used as a coloring agent in the preparation of food stuffs, a clouding agent in fruit juice drinks, and a fortifier of livestock feed and human food. Dried citrus peels or pulp by-products and waste, which are highly absorptive, have been used as poultry bedding. 
     Citrus fruit by-products, such as the peels and pulp, can be processed in many different ways to obtain food or feed additives. For example, U.S. Pat. No. 4,225,625 teaches a method for separating citrus peels into separate albedo and flavedo components for later use. In the invention taught by U.S. Pat. No. 7,060,313, citrus peel and pulp with juice removed are processed to recover components of value such as, d-limonene, molasses, pectin pomace, and food grade quality peel mass. Other methods convert dried citrus peels to animal feed, as taught by U.S. Pat. No. 2,186,907, and to food additives, as taught by U.S. Pat. No. 3,868,466. Yet another example of converting citrus by-products is provided by U.S. Pat. No. 7,629,010 which teaches methods for recovering citrus fiber from citrus vesicles using organic solvents to obtain a food additive for beverages, baked goods, meat or meat emulsions, confectionary, jams, jellies. This method uses organic solvents, as does the method taught by U.S. Pat. No. 6,183,806 for making citrus fruit peel extracts and flour. Collecting citrus oil, as taught by U.S. Pat. No. 6,151,799, is another way to process useful components from citrus peels. 
     Citrus processing creates substantial waste in the form of peels, seeds, rag, and pulp. The U.S. regulatory environment places restrictions on disposal of waste emissions from citrus plants. As a consequence, citrus peel waste cannot be dumped into landfills, but must be converted into useable products, such as stock feed. The conversion is a costly add-on expense for citrus plant operators. 
     The foregoing is believed to describe the prior art processes. While the above prior art processes provide for extracting citrus by-products for use, one drawback of the prior art is that the processes are costly and impractical because unnecessary processing steps are used, for example, separating albedo from flavedo of citrus peels. Another drawback is the need to use pollution generating solvents to extract components of citrus by-products. A further drawback is that unnecessary processing and pollution generating solvent-based processing increase operating costs and maintenance. Furthermore, the use of pollution generating solvents requires operational control to meet regulatory framework and could have an adverse impact on the environment. 
     This invention overcomes the drawbacks of the prior art. This invention provides processes to convert standard citrus waste—a high biochemical oxygen demand (B.O.D.) product—into value added commercial products, to reduce or eliminate discharge problems associated with industrial waste, to drastically reduce discharge and penalty costs for handling waste, and to provide a water-based process thus eliminating the use of environmental pollutants such as organic solvents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional aspects, features, and advantages of the invention, as to its operation, will be understood and will become more readily apparent when the invention is considered in light of the following description of illustrative embodiments made in conjunction with the accompanying drawings, wherein: 
         FIG. 1  describes the hydrolysis pathway of naringin into naringinin using the enzyme naringinase. 
         FIG. 2  is a diagram of embodiments of the invention for processes for collecting and refining citrus fiber, oil, and naringin from citrus peels; and 
         FIG. 3  is a continuation of the diagram of  FIG. 1  showing processes for collecting and refining citrus juice and naringin from citrus peels. 
     
    
    
     DETAILED DESCRIPTION 
     Over 38 million tons of citrus are used annually to produce juice. Consequently, citrus juice extraction produces significant volumes of peel, seed, rag, and pulp waste. This organic waste cannot be disposed of in a landfill because it is a high B.O.D. waste product, but must be processed into commercial products such as stock feed or citrus oils to reduce the environmental impact of the sheer volume and content of citrus waste. One purpose of the invention is to convert the standard waste—peels, residual juice, and oils—into the following commercial-ready products: high quality dietary fiber, potable citrus juice, naringin, and citrus oil. Another purpose of the invention is to reduce industrial waste created by citrus juice extraction. This reduction diminishes costs and fees for processing waste. It also mitigates risk exposure to penalties related to disposal or discharge violations. A further purpose of the invention is to eliminate pollution-generating solvents used to convert citrus waste into useable products by providing a water-based process for converting citrus peels. 
     Illustrative and alternative embodiments and operational details of the processes for converting citrus peels into fiber, juice, naringin, and oil are discussed in detail below with reference to  FIGS. 1 through 3 . The processes of the invention may take place in large scale commercial operations whereby each step is automated with industrial machinery, carried out manually, or executed with some combination of both. The term “citrus” takes on its ordinary meaning and refers generally to oranges, grapefruits, kumquats, pomelos, tangelos, citrange, citron, lemons, limes, mandarins, tangerines, and the like. 
     Citrus juice is extracted by hand or by machine from the fleshy inner part of citrus. The fleshy inner part of the citrus comprises pectinaceous and cellulosic pulp vesicles, which are also referred to as, citrus vesicles, citrus cells, pulp, or juice sacs. The phrase “juice sacs” is used generally throughout this disclosure to refer to the pulp vesicles. In commercial processing, citrus is washed, juiced, and strained to remove peel and rag. Extracting juice may be performed by separating the inner flesh from the peel with a specialized utensil and then squeezing the flesh to release juice from the juice sacs. Juice extraction may occur by automation with industrial machinery that presses whole or halved citrus to release juice from the juice sacs. Either extraction process—manual or mechanical—generates a considerable amount of peels. 
     Citrus peel waste produced by juice or fruit segmenting operations contains valuable and extractable products. For example, the juice sacs attached to cut or pressed peels—which are typically discarded—contain considerable amounts of citrus juice that can be extracted and refined for consumption. Citrus peels and juice contains bitter components, including naringin—a soluble flavanone glycoside—and limonin—a soluble furanolactone. These citrus components can be extracted with solvents such as ethanol and water and later refined for use. Naringin—a powerful antioxidant—is available commercially as a nutritional supplement. Dietary fruit fiber and citrus oil are also present in citrus peels and can also be extracted for use. 
     Extracting Juice by Pressing Citrus Peels 
     Referring to  FIG. 2 , citrus peels with residual juice sacs attached  110  are pressed  112  to release citrus juice  120  (also shown in  FIG. 3 ) from the juice sacs. The citrus juice  120  is bitter because it contains naringin and other bitter components. Conventional press equipment, such as, for example, a screw press or the like, can be used to press the peels. The press exerts pressure that can be adjusted to generate a desired yield of juice. For example, the press may be configured to exert pressure from about one psig to about 30 psig. The yield ranges from about 10% to about 60% by peel weight. This yield depends on the season of citrus harvest and the type of fruit being pressed. As shown in greater detail in  FIG. 3 , the bitter citrus juice  120  released by pressing is collected and then refined for use by a series of processing steps. 
     Referring now to  FIG. 3 , the bitter citrus juice  120  is centrifuged  122 , or alternatively filtered, to clarify the bitter citrus juice  124 . The clarified juice  124  may then be filtered  126  with ultrafiltration or other filtration mechanism configured to collect retentate  128  comprising particulate matter, which is discarded. The juice that permeates the filter  140  is then processed to debitterize  142  and decolorize  146  the juice. This debittered and decolorized juice may be frozen and stored  510 ,  512  or concentrated  148  the juice into a desired ° Brix  150  and stored frozen  176  or sterilized and stored in refrigerated conditions  152 ,  158 , as shown in  FIG. 3  and described in further detail in the later portions of this disclosure. 
     Debittering Juice 
     Referring again to  FIG. 3 , the filtered bitter citrus juice  140  is debittered  142  by a process used to remove naringin  190 . Debittering the juice improves its taste and consequently its consumer appeal. There are two processes—non-enzymatic and enzymatic—that may be used to debitter juice  142 . 
     Debittering Juice by Non-Enzymatic Processes 
     A non-enzymatic process may be used to de-bitter citrus juice  142 . A purpose for using this process is to recover naringin from the juice. Nondestructive recovery of naringin from juice uses non-ionic adsorbent resins (i.e., Mitsubishi SP710) or similar polystyrene resins designed to adsorb naringin and similar bitter components present in the citrus juice. The resins—packed into a column—are food grade polymers and may be regenerated and reused as long as the resins retain sufficient adsorptive capacity. The juice may be filtered with an ultrafiltration unit or other suitable means to remove suspended particles before the juice is passed through the resin-packed column to minimize fouling of the resin. 
     Filtered or unfiltered citrus juice is passed over the resin packed in the column at a flow rate optimized for adsorption  190  of naringin to the resin packed in the column. The flow rate may be in a range of about one bed volume (BV) to about 30 BV per hour or other preferred flow rate that maximizes adsorption of naringin. The flow rate may be optimized within a range from about 2 BV to about 5 BV per hour. The temperature of the citrus juice may range from about 32° F. to about 220° F. before, during, and after its passage through the column. In an embodiment, the juice temperature is about 70° F. The citrus juice collected from the column  144  may be cooled and stored or immediately transferred into the next phase of juice refining—the decolorizing step  146 . 
     Debittering Juice by Enzymatic Processes 
     Alternatively, enzymes, such as naringinase, may be used to de-bitter the juice  142  by partially or totally removing naringin from the juice  140 . Enzymatic processing is used if the goal is to remove, but not recover, naringin. Naturally occurring naringin is a glucoside containing a rhamnosyl group (rhamnoglucoside). Naringinase hydrolyzes the glucoside naringin converting it into naringinin (aglycone form of naringin) ( FIG. 1 ) which is not bitter. During debittering  142 , naringinase may be introduced to the citrus juice at a rate of about 0.001% to about 1.00% by weight at a temperature in a range of about 35° F. to about 150° F. Naringinase may be added to the juice  142  and held for a time ranging from about 5 minutes to about 5 hours to allow the enzyme to hydrolyze naringin dissolved in the juice. This enzymatic debittering  142  is complete when the naringin in the juice is hydrolyzed. The debittered juice  144  is then heated to a temperature ranging from about 165° F. to about 220° F. Debittered juice  144  is then cooled to about 35° F. to about 150° F. and stored or immediately transferred to the next phase of juice refining—the decolorizing step  146 . 
     Decolorizing Juice 
     Debittered juice  144  is prepared for decolorizing  146 . This preparation step differs from the process used to debitter the juice. The debittered citrus juice  144  may be filtered through ultrafiltration membranes if the juice was de-bittered with enzymes. In another embodiment, the debittered citrus juice  144  is decolorized  146  without pre-filtration if a non-enzymatic process of debittering was used. 
     The process for decolorizing juice  146  (as shown in  FIG. 3 ) involves flow processing similar to debittering  142  except for the type of adsorbent resin packed in the column. In an embodiment, the decolorizing resin is a non-ionic adsorbent resin (i.e., Mitsubishi DCA11, an acrylic resin) or functionalized adsorbent resin (i.e., Dow Amberlite™ FPX66) with a weak base anion exchange characteristic. In alternative embodiments, a weak base anion exchange resin (i.e., Mitsubishi Diaions) or a strongly basic anion exchange resin (i.e., Mitsubishi Diaions) may be used for decolorizing  146  the debittered citrus juice  144 . The resins used for decoloring are food grade polymers and may be regenerated and reused as long as the resins retain sufficient adsorptive capacity. 
     Decolorizing citrus juice  146  is accomplished by passing the juice through a column packed with a decolorizing resin. Decolorizing resin adsorbs unwanted colors and their precursors dissolved in the debittered citrus juice  144 . The flow rate of the juice allows adsorption of color materials and their precursors to the resin packed in the column. The flow rate may be in a range of about 1 BV to about 30 BV per hour or other flow rate that optimizes adsorption of color materials and their precursors. In another embodiment, the flow rate may range from about 2 BV to about 5 BV per hour. The temperature of the juice may range from about 32° F. to about 220° F. before, during, and after its passage through the column. In an embodiment, the juice temperature is about 70° F. After the debittered citrus juice  144  is passed through the column, the resin in the column may be regenerated by washing the resin to remove adsorbed color materials and their precursors. 
     Concentrating Debittered and Decolored Juice 
     Referring now to  FIG. 3 , the decolorized citrus juice  146  eluted from the column is collected and concentrated  148  into a desired brix using conventional processes. In an embodiment, the degree Brix may be 70°. Decolorized citrus juice  146  is concentrated  148  into citrus juice  150  at ambient or reduced atmospheric pressure. As a non-limiting example, the pressure may be between about one inch of mercury to about 30 inches of mercury. In an embodiment, the concentrated citrus juice  150  may be prepared for packaging by sterilizing  152  the concentrated citrus juice  150  or, in alternative embodiments, by chilling  170  the concentrated citrus juice  150 . The sterilized juice concentrate  154  may be aseptically packaged  156  and stored at ambient or refrigerated temperatures  158 . The chilled juice concentrate  172  may be packaged  174  and stored in a refrigerator or freezer  176 . 
     Alternatively, the decolorized citrus juice  146  may be frozen  510  and/or stored  512  for commercial use. 
     Extracting Naringin from Juice 
     After juice is passed through the debittering column, adsorbed naringin  190  is desorbed  192  from the resin using a solvent (as shown in  FIG. 3 ) and removed from the resin-packed column in a solution. In an embodiment, the solvent is hot water. In other embodiments, different solvents may be used, such as, for example, alcohols, combinations of water and alcohol, or other solvents capable of desorbing naringin from the resin. The solvent desorbs naringin  192  from the resin in the column in a solution  194 . The eluted naringin in solution  194  is recovered and may be crystallized  196  into pure naringin crystals  198  using conventional methods of crystallization. The naringin crystals  198  are packaged  200 . The packaging may be hermetically sealed and impermeable to moisture to prevent rehydration of the packaged naringin crystals  198 . 
     Processing Citrus Peels 
     Referring now to  FIG. 2 , the pressed citrus peels  300  are pulverized or ground in water  302  with grinding equipment to create a citrus peel slurry  304 . Conventional grinding equipment, such as, for example, a Fitzmill or the like may be used to pulverize the citrus peels. The ratio of water to pulverized citrus peel may range from about 0.1 to about 200 times peel weight. Pulverized peel particles in the slurry may range from about 0.1 mm to about 10 mm in size. In another embodiment, the particles range from about 1 mm to about 2 mm in size. The slurry may be maintained in a storage tank or the like at a temperature ranging from about 0° F. to about 170° F. for a time period of about 2 hours up to about 1 year. 
     The citrus peel slurry  304  is processed by centrifugation  310  to separate citrus peel puree  400  from liquid supernatant  350 . In an alternative embodiment, macerating enzymes  306  (for example, and without limitation, NovoShape™ from Novozymes, or CrystalZyme™ from Valley Research) is added to the citrus peel slurry  304  to create a liquefied citrus peel  308 , which is then centrifuged  310 , pressed, or filtered to separate citrus peel puree  400  from liquid supernatant  350 . Citrus peel puree  400  is then processed to extract fiber, and the liquid supernatant  350  is processed to extract oil and naringin. 
     Extracting Fiber from Citrus Peel Puree 
     The citrus peel puree  400  is then washed (as shown in  FIG. 2 ) by flushing with fresh water. The citrus peel puree  400  may be maintained with a water to peel weight ratio of about 0.1:1 to about 200:1. The effluent from the water flush may be recycled into the citrus peel slurry  304 . After at least one flushing, the suspension of water and citrus puree  402  is boiled at least once by heating the slurry to a temperature between about 130° F. to about 230° F. After boiling, the water is removed from the boiled suspension of water and citrus peel puree  400  by pressing, bag filtering, ultrafiltering, or centrifuging  406  the suspension. Conventional press equipment, such as, for example, a screw press or the like, can also be used for pressing the citrus peel puree  400 . The press may be used to exert pressure from about 0.1 psig to about 10 psig. 
     The supernatant  408 , which contains soluble flavanoids and insoluble citrus oils, is recycled into the citrus peel slurry  304  and reprocessed. The sequence of adding water to the puree, boiling the suspension of water and citrus peel puree  400 , and then removing the water from the citrus peel puree  400  may be repeated any number of times. In an embodiment, the sequence is repeated 3 times. Boiling the citrus peel puree  400 ,  402  increases solubility of the flavanoids, such as naringin. The purpose of the washing and boiling steps is to separate citrus peel fiber from the supernatant  408  comprising water, naringin, citrus oil, and the like released when pulverizing the citrus peels. The supernatant  408  is recycled into the citrus peel slurry  304 , and the citrus peel puree  400  (now referred to as citrus pulp  410 ) is processed into citrus fiber as shown in  FIG. 2  and described in further detail later in this disclosure. 
     Drying Citrus Fiber 
     Referring again to  FIG. 2 , the washed and debittered citrus pulp  410  is dried  412  into citrus fiber granulate  414  by conventional methods. The pulp  410  may be dried to reach a water content ranging from about 2% to about 95% by weight. In embodiments, the drying can occur with or without heat at atmospheric pressure. In alternative embodiments, the drying can occur with or without heat at a reduced pressure, such as under a vacuum. The washed and debittered citrus pulp  410  may be dried by other conventional methods such as, for example, freeze drying, spray drying, drum drying, Infra Red radiation, or the like. The fiber granulate  414  may be ground  416  into citrus fiber powder  418 . The fiber granulate  414  may be ground at different mesh sizes ranging from about 4 mesh Tyler to about 200 mesh Tyler or finer. 
     The fiber granulate  414  and citrus fiber powder  418  comprise mostly dried dietary fiber and pectin. The total dietary content of the particles may range from about 5% to about 95% by weight. And the soluble fiber of the particles may range from about 5% to about 95% by weight. In an embodiment, the final moisture content may range from about 0.5% to about 20% by weight. Citrus fiber granulate  414  may be packaged at various sizes. The packaging may be hermetically sealed and impermeable to moisture to prevent rehydration of the packaged citrus fiber  422 . 
     Purifying Naringin and Citrus Oil 
     Referring to  FIG. 2 , the supernatant  350  removed from the centrifuged citrus peel puree  400  comprises solubilized naringin, crude citrus oil, and other citrus peel components released from the citrus peel during grinding  302 . The supernatant  350  may be centrifuged or allowed to separate by gravity into an upper phase  354 , which contains crude citrus oil, and a lower phase  370 , which contains solubilized citrus components including naringin. The crude citrus oil is refined  356  using commercial techniques into pure citrus oil  358 . 
     The lower phase  370  of the supernatant  350 , which includes naringin, is filtered, for example, with ultrafiltration to extract soluble naringin. The retentate  394  of ultrafiltration is collected and discarded  396 . The permeate  374  of ultrafiltration is debittered  376  similar to the processes used to debitter juice. The permeate  374  of ultrafiltration is passed through a column packed with debittering resins. The resins adsorb naringin and allow most other components of the permeate to elute through the column. In an embodiment, the un-adsorbed permeate eluate  390  is recycled into the water used during citrus peel grinding  302  or, alternatively, is discarded. The adsorbed naringin  378  is then desorbed  380  from the resin using a suitable solvent, such as, for example, hot water, alcohol, or a mixture of both. The naringin solution  382  is captured and then crystallized  384  into naringin crystals  386  by conventional methods. The naringin crystals  386  are packaged and sealed into bags  200 . 
     While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embraces all such alternatives, modifications and variations as fall within the scope of the claims below.