Abstract:
Systems and methods according to the present invention yield milk products having reduced cholesterol. A method according to the present invention includes the steps of adding an edible oil to skim that was separated from whole milk; standardizing the particle size of the skim-and-oil mixture; combining the skim-and-oil mixture with homogenized cream that was separated from whole milk; and separating the oil from the reduced cholesterol cream and skim. A method according to the present invention may further include the steps of separating the reduced cholesterol cream and skim and then recombining them to form a reduced cholesterol milk product having desired properties.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to systems and methods utilized in fluid processing operations and more specifically to systems and methods for reducing cholesterol in a milk product, where the milk product may have a selective fat content. 
     Physicians and health experts generally agree that a diet low in saturated fats and cholesterol can reduce the likelihood of heart and circulatory diseases. Consumer awareness of the health benefits associated with maintaining a diet low in fat and cholesterol has recently increased, along with the demand for food products low in these components. Because of its low fat content, skim milk currently has large applications in such low fat food products. 
     Whole milk is a dilute emulsion combined with a colloidal dispersion in which the continuous phase is a solution. Whole milk has a fat content typically between about 3.3% to about 3.4% and 14 mg cholesterol per 100 g milk. To obtain skim milk, whole milk is usually centrifuged. An oil rich phase having cream floating on top and a liquid phase, or skim milk, are obtained. 
     In milk products, the majority of the fat and about 80 percent to about 85 percent of the total cholesterol is present in the cream. The cream is comprised of predominantly milk fat globules. The cholesterol in the milk fat is thought to be distributed between the milk fat globule membrane and the bulk lipid. Wong, Fundamentals of Dairy Chemistry (1988). It was once thought that when the membrane was separated from the milk fat globules and the butter oil was isolated from the milk fat globules, that about 90 percent or greater of the cholesterol was equilibrated in the butter oil and about 5 percent or greater was in the membrane. Contrary to this prior interpretation, there may actually be very little connection between cholesterol content and fat content. 
     Roughly, prior skim milk contains about 10% to about 20% of the cholesterol that is in whole milk. Skim milk contains less than about 0.5% fat, about 10% solids and typically about 2 to about 3 mg of cholesterol per 100 g of skim milk. 
     The cholesterol in milk products is thought to be associated with triglycerides, milk fat globules and complex proteins. Cholesterol in skim milk is thought to exist in three forms: (i) complexed with residual triglyceride droplets not removed in the skimming process, (ii) complexed with lipoprotein particles sloughed off from milk fat globule membranes in the skimming process, and (iii) complexed with proteins contained in the serum albumin. When skim milk, reduced-fat or whole milk is concentrated, its cholesterol content increases proportionally. For example, nonfat dry milk has a cholesterol content of about 20-30 mg per 100 grams. Therefore, the use of skim milk, reduced-fat or whole milk as an ingredient in low fat foods can contribute significant amounts of cholesterol to these foods. 
     It is therefore desirable to produce milk products that have a substantially reduced cholesterol content. A satisfactory cholesterol removal process would maximize cholesterol removal without affecting the protein functionality or other properties of the milk. A desirable removal process would be simple to perform and would minimize equipment and raw material requirements. Furthermore, the use of potentially harmful materials such as organic polar solvents would preferably be avoided. No such method is known to have been developed prior to the present invention. 
     Several approaches have been utilized for removing the cholesterol from milk fats. For instance, methods of removing cholesterol from fats by contacting with adsorbent materials such as silica gel and activated carbon. When applied to milk products, such adsorbents have been found to either be too impractical for commercial use or to lack specificity for cholesterol adsorption. Also, supercritical extraction processes have been used; however, such processes involve extreme process conditions and are generally too expensive for large commercial applications. 
     Therefore, the art of reducing cholesterol in milk products would benefit from systems and methods utilizing an edible oil for reducing cholesterol in a resulting milk product having desired fat content. 
     SUMMARY OF THE INVENTION 
     The present invention provides systems and methods utilizing an edible oil for reducing cholesterol in a resulting milk product having desired fat content. 
     In a first embodiment, a method according to the present invention includes the step of providing skim and cream, both of which may have been separated from provided whole milk. The skim is combined with edible oil, such as soybean oil, at a predetermined oil-to-skim ratio, such as one part oil to nineteen parts skim, to make a skim-and-oil mixture. The skim may be heated prior to being combined with the oil. The skim-and-oil mixture is blended, thereby forming a blended skim-and-oil mixture. The particle size of the blended skim-and-oil mixture is then standardized, thereby forming a particulated skim-and-oil mixture. The standardization of the skim-and-oil mixture may be performed by shearing the blended skim-and-oil mixture, such as by a shear pump or colloid mill. The desired particle size of the particulated skim-and-oil mixture is preferably in the range of about 0.1 microns to about 10 microns. 
     The provided cream is homogenized, thereby making a homogenized cream. The cream may be heated prior to homogenization. The homogenized cream preferably has a particle size of about 0.04 microns to about 1 micron, and more preferably has a particle size of about 0.08 microns to about 0.5 microns. A predetermined amount of the homogenized cream is combined with the particulated skim-and-oil mixture, thereby making a milk-and-oil mixture. The milk-and-oil mixture is held for a predetermined period of time at a predetermined temperature and is preferably agitated during the hold time. A majority of the edible oil is then separated from the milk-and-oil mixture, thereby leaving a first reduced cholesterol milk product. 
     In another embodiment, a method according to the present invention further comprises the step of separating the first reduced cholesterol milk product into a first reduced cholesterol skim and a first reduced cholesterol cream, either or both of which may be further separated to remove substantially all remaining oil, thereby leaving a second reduced cholesterol skim and/or a second reduced cholesterol cream, respectively. Another embodiment may include the step of combining the first or second reduced cholesterol skim with the first or second reduced cholesterol cream at a predetermined skim-cream ratio, thereby making a second reduced cholesterol milk product. 
     In yet another embodiment of a method according to the invention, any method according to the present invention is performed substantially automatically by a system after initial programming by an operator. 
     Another method according to the present invention includes the steps of providing an initial milk product—such as skim milk, 1% milk, 2% milk or whole milk—and combining the initial milk product with an edible oil at a predetermined oil-to-milk ratio thereby making a milk-and-oil mixture. The milk-and-oil mixture is blended, thereby forming a blended milk-and-oil mixture. The particle size of the blended milk-and-oil mixture is then standardized, thereby forming a particulated milk-and-oil mixture, which is held and agitated at a predetermined hold temperature for a predetermined period of time, thereby forming a modified milk mixture. A majority of the edible oil is then separated from the modified milk-and-oil mixture, thereby leaving a first reduced cholesterol milk product. 
     The method may further include the steps of providing cream and homogenizing the cream, thereby making a homogenized cream. A predetermined amount of the homogenized cream may be combined with the blended milk-and-oil mixture prior to standardizing the blended milk-and-oil mixture, thereby incorporating the predetermined amount of homogenized cream into the particulated milk-and-oil mixture. Alternatively, or additionally, a predetermined amount of the homogenized cream may be combined with the particulated milk-and-oil mixture prior to the holding and agitating steps, thereby incorporating the predetermined amount of homogenized cream into the modified milk-and-oil mixture. The method may further comprise the steps of separating whole milk to obtain the initial milk product and the cream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a first embodiment of a method for reducing cholesterol in a milk product. 
         FIGS. 2A and 2B  provide a first embodiment of a system for reducing cholesterol in a milk product. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     Turning now to the figures,  FIG. 1  presents an embodiment  200  of a method of reducing cholesterol in a milk product according to the present invention. The method  200  will be explained with reference also to the system  10  depicted in  FIG. 2A  and  FIG. 2B . The system  10  is preferably generally controlled by a programmable logic controller (PLC) that is programmable or otherwise interactive through a human machine interface (HMI), which may be provided on a touch-screen panel. Before initiating the processing of a quantity of raw whole milk  100  that has been received  211 , the PLC may require some programming input from a system operator. For instance, the operator may program the PLC with the whole milk batch size to be processed. Other parameters will be discussed throughout the remaining description. 
     Depending on the implementation of the system  10 , some manual swing connections may be required to establish desired or required fluid flow paths. For instance, flowverter panels may be used to direct fluid flow. Flowverter panels may be used, for example, to insert or remove optional equipment from the fluid flow circuit. Once the manual swing connections have been made, if needed, the generally automated process may begin. 
     The method  200  generally begins when after whole milk  100 , which may be raw, is received  201 . The raw whole milk  100  is delivered to a processing site having a receiving capacity, which may be, for example, 3000 gallons. The delivery  201  may be made to a processing site by way of a delivery vessel  12 , such as a tank carried by a truck. The delivery vessel  12  is preferably coupled to a receiving pump  14 , which conveys the raw whole milk  100  from the delivery vessel  12  to a receiving tank  16 . A flowmeter (not shown) may be installed in the flow path from the delivery vessel  12  to the receiving tank  16  to monitor the amount of product pumped into the tank  16  to assist in preventing overflow. A level transmitter (not shown) may be operatively coupled to the receiving tank  16  to provide an overflow or desired level emergency alert, also to assist in preventing an overflow condition. Upon completion of receiving  201  the raw whole milk  100 , the receiving line  15  may be air blown by way of an air blow check valve and an air solenoid valve, which reside generally at opposite ends of the receiving line  15 . Alternatively, rather than receiving raw whole milk  100 , the process may begin by receiving raw skim and raw cream which have been separated from raw whole milk. Generally, the whole milk  100 , or other supplied cream and skim, is received into the receiving tank  16 , which may keep the delivered product at a desired temperature, such as approximately forty degrees Fahrenheit. 
     After the delivery  201  of raw whole milk  100 , the method  200  generally includes a whole milk separation step  203 , using a separator  22  to separate the raw whole milk  100  into skim  102  and cream  104 . While the process herein describes use of skim  102  and cream  104 , it is to be understood that the skim  102  is provided as an initial milk product, but other initial milk products are contemplated. Thus, the process may be run on an initial milk product that is, for example, one or two percent milk, or whole milk. The whole milk  100  is preferably heated prior to separation  203 , perhaps by flowing through a whole milk heat exchanger  20 , thereby creating a heated whole milk  101 . The whole milk  100  may be heated to any desirable temperature that will maintain integrity of the milk  100 , but a temperature of about ninety-five degrees to about one hundred and ten degrees Fahrenheit, and more preferably a temperature of about one hundred and five degrees Fahrenheit, produces desirable results. Any heating or pretreatment of the whole milk  100  prior to separation  203  may depend upon the type of separator being employed, e.g., a centrifugal separator or membrane filtration unit. 
     After separation, the skim  102  and the cream  104  are preferably processed in parallel before being rejoined in the agitation tank  56 , if cream  104  is rejoined. The separated skim  102  is preferably heated  205 , such as by flowing through a skim heat exchanger  24 , preferably to a temperature of between about 120 to about 150 degrees Fahrenheit, and more preferably from about 135 to about 140 degrees Fahrenheit, thereby creating a heated skim  106 . The heated skim  106  is then added to a mixing tank  26  to be combined  213  with a quantity of desired edible oil  108 , such as soybean oil, that is usually stored onsite  211 . In fluid communication with the mixing tank  26 , is a supply  211  of edible oil, which may be, for example, a 4×4×4 portable oil tote having a capacity of approximately 360 gallons. As the heated skim  106  is delivered to the mixing tank  26 , oil  108  from the supply  211  is metered into the tank  26 . The amount of oil  108  is based upon an oil-to-skim ratio that is predetermined before starting the substantially automated process and is programmed into the PLC through the HMI. The desired oil-to-skim ratio may range from 1:1 to 1:99, but preferably is about 1:19. Although any suitable blending device may work, a preferred mixing tank  26  is a Breddo Likwifier™ available from American Ingredients Company of Kansas City, Mo. While a single tank  26  is shown, a plurality of tanks  26  may be cascaded to accommodate various production capacities. The flow of skim  106  to the mixing tank  26  may be monitored by a flowmeter (not shown), and the mixing tank  26  may be provided with level indicators, which are utilized for high level alarm while filling. If a plurality of mixing tanks  26  is used, the system  10  may automatically fill each of the plurality of tanks  26  in succession, based on a whole milk batch size entered into the HMI and recorded by the PLC. Upon or near the completion of the filling cycle of the mixing tank  26 , the skim-and-oil mixture may be blended. The blend time is preferably predetermined and set on the HMI prior to starting the process, but is preferably on the order of about one to about ten minutes, and more preferably about 3 to about 5 minutes. Where a plurality of mixing tanks  26  are used, the blending process may begin while successive tanks  26  are being filled with the skim  106  and oil  108 . Alternatively, or additionally, to the skim  106  and oil  108  being mixed in mixing tanks  26 , oil  108  may be introduced into the fluid flow conduit of the skim  106 , perhaps eliminating the need for a mixing tank  26 . 
     The blended skim-and-oil mixture  110  may be pumped by a pump  30 , which may be a positive pump, to a shearing device  32 , such as a colloid mill. Other shearing or blending devices could be used, such as a shear pump, a hydroshear device, a high level shear mixer, or even a homogenizer, although the latter may be less desirable based on desired particle size. An example of a high level shear mixer that may be employed is a Quadro Ytron Z Emulsifier, available from Quadro (US) Inc. of Millburn, N.J. The shearing device  32  is used to shear  215  the skim-and-oil mixture  110  to, at least in part, standardize the particle size of the mixture  110  prior to being added to a processing tank  56 , thereby forming a particulated skim  112 . As used herein, “particle size” refers to the preferred maximum dimension through the geometric center of any particle of a given mixture. For instance, the particle size of a spherical particle would be its diameter. The desired particle size of the mixture  112  prior to being added to the processing tank  56  is about 0.1 micron to about ten microns. The shearing is preferably carried out at a pressure of about fifty to about 2000 pounds per square inch (psi), and more preferably at a pressure of about 850 to about 950 psi, and more preferably at a pressure of about 900 psi. The particulated skim  112  is then added to the processing tank  56 , to which cream may be added, which may have been processed substantially in parallel. 
     Turning now to the preferably parallel processing of the separated cream  104 , the cream  104  is preferably heated  207  and then homogenized  209  prior to being added to the processing tank  56  with the skim-and-oil mixture  110 . While the heating  207  of the cream  104  is optional, it may be desirable prior to homogenization  209  as it has been found to improve flavor of the resulting product. Cream heating  207  may be provided by causing the separated cream  104  to flow through a cream heat exchanger  42 , thereby creating a heated cream  114 . A preferred temperature range for the heated cream  114  is about 145 to about 170 degrees Fahrenheit, and more preferably about 165 degrees Fahrenheit. The heated cream  114  may be forced through the cream heat exchanger  42  by a pump  40 , which may be a positive pump, to maintain a relatively constant pressure supply to the homogenization  209  step. While a single homogenizer may be used, two or more optional homogenizers may be provided. The direction of heated cream  114  to a desired homogenizer  52  or  54  may be provided by a flowverter panel  44 . For instance, a larger 10,000-lb. batch homogenizer  52  and a smaller 700-lb. batch homogenizer  54  may be provided. The speed of the pump  40  is controlled to maintain a relatively constant inlet pressure on the selected homogenizer, which may be measured by a pressure transducer (not shown). If the smaller homogenizer  54  is used, the flowverter  44  is switched to divert the cream  114  to the small homogenizer  54  and by-pass a hold tube  48 , cream cooler heat exchanger  50 , and larger homogenizer  52 . The smaller homogenizer  54  then homogenizes  209  the provided cream  114  at a predetermined pressure. If the larger homogenizer  52  is used, the flowverter  44  is switched to divert the cream  114  through a hold tube  48 , which provides a hold time, or travel time, of preferably about twenty-one seconds at a predetermined flow rate, such as about 4.6 gallons per minute. The cream  114  is then preferably cooled through a cream cooler heat exchanger  50 , thereby producing cooled cream  116  that may be presented to the larger homogenizer  52 . The temperature of the cooled cream is preferably about 120 degrees to about 150 degrees Fahrenheit, and more preferably about 135 degrees to about 140 degrees Fahrenheit. The cooled cream  116  is then provided to the large homogenizer  52  for homogenization  209 . Regardless of which homogenizer is used, the homogenization  209  occurs at a predetermined pressure, which is preferably about 2,000 to about 5,000 pounds per square inch, and more preferably at about 250 bar or about 3,600 to about 3,650 pounds per square inch. The resulting homogenized cream  122  includes at least substantially homogeneous particles having preferred sizes from about 0.04 microns to about 1 micron, and more preferably about 0.08 microns to about 0.5 microns. A predetermined amount, including none, of the homogenized cream  122  is then provided to the processing tank  56 , therein joining the particulated skim-and-oil mixture  112 . While described and shown as being added to the particulated skim-and-oil mixture  112 , a predetermined amount of homogenized cream  122  may alternatively be added prior to the standardization process  215  to the blended skim-and-oil mixture  110 . If the homogenized cream  122  is added prior to the particle size standardization  215 , the shearing is preferably carried out at a lower pressure, preferably about 125 to about 160 psi. A plurality of processing tanks  56  may be provided, if desired to handle the volume of the process. 
     Regarding the processing tank  56 , the tank  56  may be a zoned jacketed tank, which may be provided with level indicators (not shown) and an agitator, such as a batch pasteurization tank. During the filling of the processing tank  56  with the sheared skim-and-oil mixture  112  and the homogenized cream  122 , the agitator and various jacket zones are controlled. For instance, when the tank  56  is approximately five percent full, the agitator may begin, rotating at a top speed of preferably about five to about thirty revolutions per minute, and more preferably at a top speed of about twenty-five revolutions per minute. Also when the tank  56  is about five percent full, hot water may be introduced into a bottom zone of the tank jacket. The temperature control for the heating media used in the tank jacket is controlled by way of a cascade proportional, integral, derivative (PID) loop, as is known in the art. When the tank  56  is about twenty percent full, hot water may be introduced into a lower side zone of the tank jacket, and when the tank  56  is about sixty percent full, hot water may be introduced into a top side zone of the tank jacket. While the hot water used in the jacketed tank  56  may be provided by any suitable source, the jacket water source is preferably coupled to the same hot water supply that provides hot water to the various heat exchangers in the system  10 . The skim-and-oil mixture  112  and cream  122 , having been combined to form a milk-and-oil mixture within the tank  56 , is held and agitated at a predetermined rate for a predetermined amount of time at a predetermined temperature, the parameters for which may be entered into the HMI prior to processing by the system  10 . The predetermined length of time for holding and agitating the milk-and-oil mixture is preferably about five minutes to about 120 minutes, and more preferably about twenty to about sixty minutes. The predetermined agitation rate is mentioned above, but is generally a relatively mild agitation. The predetermined temperature of the milk-and-oil mixture in the tank  56  is preferably about 120 degrees to about 150 degrees Fahrenheit, and more preferably about 130 degrees to about 140 degrees Fahrenheit, and more preferably about 135 degrees Fahrenheit. 
     After the milk-and-oil mixture has been held and agitated  217  for the desired time, the mixture  124  may be transferred out of the processing tank  56 , preferably at a rate of about twenty-four gallons per minute. The transfer may be aided by a pump  58  and the milk-and-oil mixture  124  is preferably cooled through a milk-and-oil mixture cooler heat exchanger  60 , to form a cooled milk-and-oil mixture  126 . The temperature of the cooled milk-and-oil mixture  126  may be any desired temperature suitable for the next separation  219 , but the temperature is preferably about 105 degrees Fahrenheit. The cooled milk-and-oil mixture  126  is presented to a separator  62  for a milk-and-oil separation  219 . The separator  62  performs a separation  219  of a majority of the edible oil from a first reduced cholesterol milk product  130 , sending waste oil  128  to a waste oil tank  65 , which may be used as a basis for biodiesel fuel, as an ingredient for food products such as mayonnaise, or potentially as food for animals. The first reduced cholesterol milk product  130  may be held  221  in a surge tank  66 , if desired for process flow. From the surge tank  66 , the first reduced cholesterol milk product  130  may actually be packaged and sold as an end product  237 , in and of itself, perhaps as an ingredient for further processing. 
     Alternatively, further processing may be performed. For instance, the first reduced cholesterol milk product  130  may include some residual oil, which may be addressed in at least a couple of ways. A second milk-and-oil separation  224  may be performed, thereby attempting to separate additional waste oil  223  from a second reduced cholesterol milk product  226 , and the second reduced cholesterol milk product  226  may be packaged and sold as an end product  239 , in and of itself. 
     Preferably, however, a second milk separation  225  is performed on the first reduced cholesterol milk product  130 . The first reduced cholesterol milk product  130  is provided to an additional separator  70  from the surge tank  66  by a pump  68  at a desired flow rate, such as about twenty-five gallons per minute. While shown in  FIG. 3  as utilizing an additional separator  70 , the separation  225  may be performed by the same separator  22  that performed the initial whole milk separation  203 , rather than requiring the additional separator  70 . If this is desirable, the separator  22  is preferably cleaned during the time in which batch processing  217  occurs in the processing tank  56 . Regardless of which separator is used, the separation results in a first reduced cholesterol skim  132  and a first reduced cholesterol cream  136 . The first reduced cholesterol skim  132  is preferably chilled by a first reduced cholesterol skim heat exchanger  73  to a preferred storage temperature, to provide a cooled first reduced cholesterol skim  134  to be stored in a first reduced cholesterol skim storage tank  74 . The first reduced cholesterol skim  132  is cooled to a temperature of preferably about forty-five degrees Fahrenheit or below, to form the cooled first reduced cholesterol skim  134 . Alternatively, rather than being chilled and stored after the separation  225 , the first reduced cholesterol skim  134  may be processed through another separation  228 , resulting in a second reduced cholesterol skim  230  and further waste oil  223 . Thereafter, the second reduced cholesterol skim  230  may be chilled and stored in a similar manner as described in connection with the first  132 . 
     The first reduced cholesterol cream  136 , although it could be packaged and sold in its present form, is preferably separated again  231 . The first reduced cholesterol cream  136  is preferably fed to another separator  78 , perhaps by way of a positive pump  77 . This separation  231  results in a second reduced cholesterol cream  140  and more waste oil  138  which is fed  223  to the waste oil tank  65 . The second reduced cholesterol cream  140  is then preferably cooled to a predetermined temperature by a second reduced cholesterol cream cooler heat exchanger  84  to form a cooled second reduced cholesterol cream  142 , which may be fed into a storage tank  86 . The predetermined temperature to which the second reduced cholesterol cream  140  is cooled is preferably about forty-five degrees Fahrenheit or below, and more preferably about forty degrees Fahrenheit. 
     Desired products are then mixed  235  to form a final end product to be shipped  241 . In the system  10  depicted in  FIG. 3 , a cooled first reduced cholesterol skim  134  and a cooled second reduced cholesterol cream  142  are combined in a predetermined ratio to form a reduced cholesterol milk product  144  having desired properties. The predetermined ratio may include zero percent of either of the products to be mixed where, for example, only the skim or only the cream is to be provided as the reduced cholesterol milk product  144 . An on-line solids/fat sensor may be used to standardize the reduced cholesterol milk product  144  to a predetermined milk fat percentage, such as two percent. The milk product  144  may then be stored in a storage tank  92 , preferably at a predetermined temperature, to await pick-up. A centrifugal pump  94  may be provided to assist in the transfer of the milk product  144  to a delivery vessel  13 , which may be a tanker truck. While the mixing step is shown utilizing a first reduced cholesterol skim  134  and a second reduced cholesterol cream  142 , it is to be understood that the mixing step  235  may combine any of the reduced cholesterol products, such as the first reduced cholesterol milk product  130 , the second reduced cholesterol milk product  226 , the first reduced cholesterol skim  132 , the second reduced cholesterol skim  230 , the first reduced cholesterol cream  136 , and/or the second reduced cholesterol cream  140 . 
     The system  10  may also utilize a plurality of balance tanks, such as those  71 ,  76 , and  80  shown in  FIG. 3 , to ensure generally continuous process flow for processing a desired amount of end product. Additionally, the system  10  may incorporate a clean in place (CIP) system for cleaning the respective tanks and fluid flow conduits. 
     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.