WO1994012061A1

WO1994012061A1 - Lower cholesterol egg yolk method

Info

Publication number: WO1994012061A1
Application number: PCT/US1993/011418
Authority: WO
Inventors: Cecil T. Massie
Original assignee: Source Food Technology, Inc.
Priority date: 1992-11-24
Filing date: 1993-11-23
Publication date: 1994-06-09
Also published as: AU5676694A; MX9307315A

Abstract

A process for the continuous removal of cholesterol from an egg yolk material comprising wet milling said egg yolk material with an extraction oil, centrifuging said egg yolk material and extraction oil into a first egg yolk-containing fraction which is low in cholesterol and a second oil fraction which is high in cholesterol, wherein said second oil fraction is then subjected to steam stripping wherein a vapor phase rich in cholesterol and a liquid phase containing oil are produced, said liquid phase being recycled as an extraction oil for said wet milling.

Description

LOWERED CHOLESTEROL EGG YOLK METHOD

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of copending application ser. no. 07/886,266, filed May 20, 1992, which in turn is a continuation-in-part of serial no. 634,754, filed December 27, 1990, which in turn is a division of serial no. 310,536, filed Feb. 13, 1989, now U.S. Patent 4,996,072, granted Feb. 26, 1991, which in turn is a continuation-in-part of serial No. 20, 613, filed March 2, 1987, now U. S. Patent No. 4,804,555, which in turn is a continuation-in-part of now abandoned serial no. 921,984, filed October 21, 1986.

This application incorporates by reference the entire text of the aforementioned U.S. Patent 4,996,072, granted Feb. 26, 1991, "Physical Process for the Deodorization and/or Cholesterol Reduction of Fats and Oils", including the entire specification and all drawings. This application also incorporates by reference the specification and drawings of ser. no. 07/886,266, filed May 20, 1992, hereinafter referred to as the "Massie Application". BACKGROUND OF THE INVENTION

Fioriti et al., U.S. Patent 3,717,474, in Example VI, col. 4, lines 6 et seq. , blends egg yolk with oil at full speed of 7,000 rpm for a period of 15 minutes at a temperature that is said to be held between 125° F and 135° F. It is an essential element of the Fioriti process that he use "a high shear mixer capable of imparting the needed energy to disrupt the * * * water barrier in the yolk". Col. 2, lines 39-43. The Fioriti process apparently is started at a lower temperature and then rises during the 15 minute period, as it is an object of Fioriti to provide increasing temperatures due to his finding that "[t]he amount of cholesterol extracted varies directly with the increase in temperature due to the high energy blending" that is an essential element of his process. Col. 4, lines 52-54. The only temperature restriction at the high end by Fioriti is that the temperature should not exceed "much above 149° F * * *". Col. 4, lines 54-55. According to the teachings of Fioriti, Fioriti is able to extract 74.85 % of the cholesterol from egg yolk, which led to an improvement patent to Bracco, U.S. Patent 4,333,959, which provided a decrease in cholesterol level of between 79 and 80 %. Table I, column 4, lines 59-59. Bracco modified the Fioriti process by addition of strong mineral acid to destabilize the emulsion of the egg yolk. Thus, Bracco uses a process going away from the direction of the present invention, by focusing upon the inclusion in the egg yolk of a mineral acid.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided an improvement in the process of removal of cholesterol or fat from an egg yolk fraction through the admixture of said egg yolk fraction with an oil and centrifugation thereof to yield an egg rich lowered cholesterol centrifugate, the improvement comprising the intimate admixture for a period of at least about three minutes, and preferably at least about five minutes, of up to about two parts of edible oil per part by weight said egg yolk fraction under conditions of low shear substantially in the absence of air, preferably through use of a partial vacuum, at a temperature maintained within the range of from about 90° F to up to about 130° F, preferably about 115° F to about 125° F.

A benefit of the present invention is that in addition to the reduction of the cholesterol content of the egg yolk, fat reduction may be achieved in accordance with the present invention.

In accordance with a second aspect of the invention there is provided an improvement in the process of removal of cholesterol or fat from an egg-containing mixture which is blended with an oil for a period of at least three and preferably at least about five minutes that is followed by centrifugation and separation of the cholesterol-reduced egg yolk centrifugate, which improvement comprises conducting the blending substantially in the absence of air, preferably through use of a partial vacuum, at a temperature of from about 90° F to up to about 130° F, preferably about 115° F to about 125° F.

In accordance with a third aspect of the invention there is provided a process for removal of cholesterol or fat from an egg yolk fraction through an at least two stage process of (a) admixing said egg yolk fraction with an oil with said egg yolk fraction substantially in the absence of air, preferably through use of a partial vacuum, for a period of at least three and preferably at least about five minutes at a temperature of from about 90° F to about 130° F, preferably about 115° F to about 125° F followed by centrifugation to yield a cholesterol-lowered egg yolk product; and (b) repeating step (a) using said cholesterol-lowered egg yolk product in lieu of said egg yolk fraction, whereby the resultant egg yolk fraction retains the characteristics of egg yolk necessary for baking while having a highly reduced cholesterol content versus that of a raw egg yolk.

In accordance with a fourth aspect of the invention there is provided an improvement in the process for the continuous removal of cholesterol from an egg yolk material which comprises

(a) wet milling said egg yolk material having an elevated cholesterol level with an extraction oil whereby there is formed a mixture of the egg yolk material and extraction oil;

(b) centrifuging said mixture to yield a first egg yolk- containing fraction low in cholesterol, said first egg yolk- cόntaining fraction being suited for incorporation into a foodstuff, and a second fraction which is an oil feed having a high level of cholesterol; (c) introducing said oil feed at a temperature of at least about 400° F. at an upper portion of a countercurrent thin-film steam stripper while simultaneously introducing steam at a lower portion thereof, wherein said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil, said countercurrent thin-film steam stripper being continuously maintained at a temperature of at least about 400° F. , preferably at a pressure of at least about 1 mmHg, whereby there is produced a two phase exit flow therefrom comprising a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol; (d) and recycling said liquid phase as an extraction oil for said wet milling, wherein the improvement comprises wet milling said egg yolk material having an elevated cholesterol level with an extraction oil in step (a) substantially in the absence of air, preferably through use of a partial vacuum, for a period of at least three minutes at a temperature of from about 90° F to about 130° F.

UNITS OF MEASUREMENT

Throughout the specification and claims, percentages and ratios are by weight and temperatures in degrees Fahrenheit unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the removal of cholesterol from wet egg yolk using an edible oil as extraction solvent. As distinguished from earlier processes, this process achieves near theoretical extraction efficiency without contamination of the egg yolk with solvents or additives. A further advantage of this invention is that the extraction oil byproduct produced from this invention has a high cholesterol concentration, is directly suitable for recovery by steam distillation in accordance with the process of the Massie Application and may be more economically recovered due to high concentration and low mass flow as compared to the yolk.

Natural whole egg is a nutritious food with high bioavailability of essential proteins and other nutrients. In recent years per capita egg consumption has declined sharply after recommendations from national health organizations to reduce consumption of eggs due to their comparatively high cholesterol content. A single egg contains on average 213 mg compared with a recommended daily limit of dietary cholesterol of only 300 mg per day in the typical adult diet.

All prior art processes for the removal of cholesterol have in common the disruption of the low density lipoprotein macromolecule in which the cholesterol resides. The low density lipoprotein macromolecule is made up of proteins, moisture, and lipids including cholesterol and neutral triglycerides. J. Food Science 43 1210-14. The low density lipoprotein macromolecule can be disrupted by a number of means including heating, freezing, pH change, addition of sodium chloride, and dehydration. While processes based on the use of edible oils as the extraction solvent have many appealing features, they have not gained commercial success to date. The only commercially available cholesterol reduced liquid whole egg product is currently produced by a beta-cyclodextrin process. This failure of edible oil based processes to achieve success in the marketplace appears related to both functional and economic considerations. Fioriti reported that egg yolk extracted only with vegetable oil suffered a substantial loss of baking functionality. While Bracco was able to achieve a higher extraction efficiency and reports improved baking performance, this was achieved only by changing the pH of the egg yolk with strong mineral acids.

In accordance with the present invention, a process is provided that achieves high cholesterol reduction that may be based upon an edible oil as the extraction media while substantially retaining the baking functionality of the yolk.

A second major impediment to the application of edible oil extraction based processes has been the relatively unfavorable economics of oil use and recovery. A significant advantage is gained by reducing the amount of oil required or in other words, increasing the concentration of cholesterol in the extraction oil. Earlier processes produced relatively dilute solutions of cholesterol in oil typically on the order of one fifth or less of the original egg yolk concentration. It is an objective of this process to reduce oil use by increasing the concentration of the cholesterol in the extraction oil to approximately 40%. of the concentration in the egg yolk. A further economic feature of this invention is reduced cost of oil recovery and reuse. Even though efforts in the art generally have sought to provide that extraction oil should be recovered and reused to minimize the operating cost of the system, processes developed in this art to date have not presented an integrated system that permits economic recovery and reuse of the extraction oil. In particular, the extraction process must avoid the creation of contaminants which are difficult or impossible to remove from the extraction oil and which would prevent its reuse.

In accordance with the present invention, the general method of Marchner et al., U.S. Patents 4,804,555 and 4,996,072, is utilized, which method has been used for cholesterol removal from edible oils. It has been discovered that in accordance with the present invention the extraction oil is directly compatible with a steam distillation step without expensive preprocessing. This is distinguished from a system that would utilize the Bracco technology due to the inclusion in the oil fraction residue of trace amounts of mineral acid that would rapidly corrode the distillation system equipment. While oil washing is a well known process it is an unnecessary expenditure with the present invention because only edible oil is used in the extraction step.

Remarkably the product of the invention exhibits good baking characteristics, retaining about 65% of the functionality of fresh yolks. In addition there is up to 50% reduction in the fat content of the recovered yolk.

A further feature of this invention is that it can be applied without apparent difference to fresh or frozen egg yolk. Other related processes have reported difficulty with frozen egg yolks due to the presence of gelation sites in frozen egg yolk and a permanent viscosity increase which occurs with freezing. Similarly the process operates without regard to whether the yolks have been pasteurized. As a practical matter, the ability to use fresh, frozen or pasteurized egg yolk permits use of the process of this invention on a commercial scale without dependence on a nearby or attached egg breaking operation. Due to the economical use of extraction oil, smaller facilities can more readily afford to practice this invention on a modest scale.

This process is also substantially independent of the extraction oil source. In particular, animal fats such as beef fat or chicken fat which have fatty acid profiles similar to eggs can be used with the same effect as vegetable oils without causing a shift in the fatty acid profile of the product.

Finally, it has been generally assumed the extraction oil must be substantially free of cholesterol in order to achieve maximum extraction efficiency. It has been found that esterified cholesterol has no significant effect on the extraction efficiency under this invention with the result that commercially available steam distillation processes for removal of non-esterified cholesterol can be used to regenerate the extraction oil for reuse.

In the specification including claims there are several terms which are used that are defined as follows:

"Egg yolk fraction" means the yolk of an egg that is either from fresh eggs or from egg yolk that has been thawed from a previously frozen state, or a pasteurized egg yolk. A pure, fresh and unbroken egg yolk may be included as the egg yolk fraction without prior disintegration of the low density lipoprotein macromolecule that is made up of proteins, moisture, and lipids including cholesterol and neutral triglycerides. One of the advantages of the present invention is that it is not necessary to have prior disintegration of the low density lipoprotein macromolecule for the egg yolk fraction of the present invention. "Egg yolk material" is broader than "egg yolk fraction" and includes any yolk containing material including conventional egg yolk materials that have been subjected to cholesterol treatment including any material such as disclosed in the Marchner patent.

"Edible oil" means an oil of animal or vegetable origin having a food component that can be assimilated by a mammal.

By "edible oil source" is meant any oil from either animal fats such as beef fat or chicken fat which may or may not have fatty acid profiles similar to eggs or vegetable oils which do not provide a material shift in the fatty acid profile of the resultant product. In accordance with the present invention, it is not necessary to add a mineral acid as in Bracco because in accordance with the present invention there is provided a more gentle treatment of the yolk, which permits at least two extractions of the yolk without losing baking functionality of the yolk. With a two cycle treatment that is occasioned by the more gentle treatment of the present invention, it is possible to achieve a net 89 % cholesterol reduction.

By conditions "substantially in the absence of air" there is contemplated an environment where air is generally unable to substantially infiltrate the egg yolk fraction. Such conditions can be obtained, for example, by using a vessel that is completely filled substantially without air, such as by inclusion of a flexible membrane that can be expanded to occupy the space otherwise enjoyed by gas. In a preferred embodiment, however, instead of using a closed chamber, a partial vacuum is employed to provide the "conditions substantially in the absence of air." By having "conditions substantially in the absence of air" it is permitted to have a drop in the oil ratio and the use of a low shear operating condition, which latter point is highly desirable in that it permits at least two passes of the egg yolk fraction through the oil. Where "conditions substantially in the absence of air" are obtained solely due to the use of a partial vacuum, by "partial vacuum" is contemplated a vacuum of from about 300 about 1000 millibars, and preferably from about 500 to 900 millibars.

"Low shear" refers to conditions of shear more precisely known as the sheer decline of up to about 20,000 inverse seconds and preferably in the range of from about 5,000 to about 12,000 inverse seconds. A uniform low shear is obtained by using a rotor-stator design in which shear force is more selectively transmitted to the bonds in the media being milled. As a result, a larger amount of the mixing energy is used to overcome the binding energy of the low density lipoprotein macromolecule in which the cholesterol resides, and less is dispersed as heat into the media at large. As a suitable rotor-stator design mixer may be mentioned the Fryma VK-7 is produced by Fryma-Maschinen AG, CH-4310 Rheinfelden, Switzerland. In a theoretically perfect extraction of cholesterol from egg yolk, the non-esterified concentrations as measured in weight percent in the yolk and oil fractions are identical. The process of the present invention approaches this theoretical value for the elimination of cholesterol in a two stage cycle of the egg where 89 % of the cholesterol is removed.

In a preferred embodiment as set forth in Examples I-III, cholesterol is extracted from wet egg yolk in an at least two stage process producing a reduced cholesterol egg fraction and an extraction oil with high cholesterol concentration. Most preferably, the flow of oil and yolk is countercurrent resulting in the highest cholesterol concentration for distillation. The extraction oil is recovered for reuse by a steam distillation process.

Cholesterol is extracted from wet egg yolk in two stages using a countercurrent flow of edible oil as the extraction media. For the purposes of the discussion of this embodiment the first stage refers to fresh or virgin egg yolk material and the second stage refers to egg yolk recovered from the first extraction step by centrifugation.

The Massie Application provides a method for reducing the cholesterol level of an oil feed comprising introducing an oil feed having an elevated cholesterol level in comparison to a desired cholesterol level at a temperature of at least about 400° F. at an upper portion of a countercurrent thin-film steam stripper while simultaneously introducing steam at a lower portion thereof, wherein said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil, said countercurrent thin-film steam stripper being continuously maintained at a pressure of at least about 1 mmHg and a temperature of at least about 400° F. , whereby there is produced a two phase exit flow therefrom comprising a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol. The countercurrent thin-film steam stripper should be internally provided with sufficient evaporative effective surface area such that said countercurrent thin-film steam stripper is capable of removing at least 65 % of the cholesterol from a cholesterol-containing oil. Thus, said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil. In different words, the apparatus used in accordance with the invention has a greatly enlarged number of theoretical plates as distinguished from the simple use of an "unpacked" apparatus, i.e., one without a high number of theoretical plates when applied to cholesterol reduction. Accordingly, it is understood that "capable of removing at least 65 % of the cholesterol from a cholesterol-containing oil" refers to the ability of the system used in accordance with the invention to eliminate a large amount of cholesterol. It is to be understood that even if the system of the present invention is used, one skilled in the art could still find ways to circumvent the advantageous results, for example, by passing a large volume of feed oil through the system with a de minimis residence time in the system. In such a case, the user would repeat the process several times or end up with less than an optimum reduction of cholesterol. In accordance with a preferred embodiment, the method is operated under conditions to remove at least fifty percent of the cholesterol from said oil feed. In a further preferred embodiment, at least 65 % of the cholesterol is in fact removed from said feed oil.

In the Massie Application, any oil may be used as the oil feed in the practice of the invention, including oils that are mixed with vegetable oils. In a preferred embodiment, the feed oil is a fish oil, animal fat or oil, marine fat or oil, dairy fat or oil. In another embodiment, the feed oil is a dairy fat or oil. In yet another embodiment, said feed oil is a dairy fat or oil which is anhydrous butterfat or milkfat. And, in a still further embodiment, the feed oil is an animal fat.

The thin-film stripper of the present invention should be maintained at a temperature of at least about 400° F. , preferably using an internal circulation of auxiliary heating media through the stripper's plumbing to provide further indirect heating of the oil for process control. Distinguishing the present invention from previous thin-film strippers is not only the use of a cholesterol-containing oil, but also the arrangement of the apparatus to provide for a sufficient effective evaporative surface to permit a high level of the cholesterol to be removed. Thus, the stripper as used in the prior art is commonly referred to as a tube and disc type evaporator. Generally in the prior art this type of equipment is used for different purposes, namely solvent recovery, e.g. , hexane removal from soybean oil, and thus typical industrial focus has been given to optimization of the distillate fraction. The thin-film stripper may, for example, be arranged to have a larger interior surface area and thereby to greatly increase the evaporative surface area in comparison with the conventional use of otherwise identical equipment. The arrangement used in accordance with the present invention provides for the number of theoretical plates to be dramatically increased and thus mass transfer rates increased so as to effect removal of the non-esterified cholesterol notwithstanding any similarities between the operating conditions and residence times of conventional steam stripping deodorization and the present method.

In accordance with a second aspect of the Massie Application there is provided a process for the continuous removal of cholesterol from a feed oil which comprises (a) wet milling a raw oil having an elevated cholesterol level with an extraction oil whereby there is formed a mixture of the raw oil and extraction oil; (b) centrifuging said mixture to yield a first fraction low in cholesterol, said first fraction being suited for incorporation into a foodstuff, and a second fraction which is an oil feed having a high level of cholesterol; (c) introducing said oil feed at a temperature of at least about 400° F. at an upper portion of a countercurrent thin-film steam stripper while simultaneously introducing steam at a lower portion thereof, wherein said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil, said countercurrent thin-film steam stripper being continuously maintained at a pressure of at least about 1 mmHg and a temperature of at least about 400° F. , whereby there is produced a two phase exit flow therefrom comprising a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol; (d) and recycling said liquid phase as an extraction oil for said wet milling.

In step (a) of wet milling a raw oil having an elevated cholesterol level with an extraction oil whereby there is formed a mixture of the raw oil and extraction oil, the amount of raw oil yolk versus the amount of extraction oil, whether recycled or freshly introduced, is from about one to about four parts by weight of extraction oil per part raw egg oil, and more preferably about two parts extraction oil per part raw egg oil.

The wet milling of the present invention involves mixing the ingredients in a high intensity mixer of the type that can be used for making mayonnaise. In a preferred embodiment there is used the Fryma VK-7 apparatus.

The extraction oil that enters the wet milling process at the commencement of any production run may be either leftover extraction oil from a previous run, extraction oil that has been recycled, fresh oil, or any combination thereof. When a fresh oil is introduced into the procedure, the oil may be of animal or vegetable origin. As examples of oils that may be used as the extraction oil may be mentioned vegetable and animal oils. As vegetable oils may be mentioned soy oil, corn oil and safflower oil. As animal oils may be mentioned lard, tallow, chicken fat or a marine oil, e.g., a fish oil. In one preferred embodiment chicken fat is used as the extraction oil.

Whereas it was indicated in the Massie Application that the temperature of step (a) is not particularly critical, in accordance with the present invention step (a) should be conducted under the temperature conditions of the first aspect of the invention below 130° F and above 90° F and most preferably in the range of 115° F to 125° F. It is recognized that the extraction oil that is recovered in step (c) is at a temperature of at least about 400° F when it exits the steam stripper. Preferably, the oil is permitted to cool, for example, to room temperature, but it may be used without such cooling, preferably at a temperature of up to about 130° F. The raw oil of the Massie Application in accordance with the present invention is the egg yolk fraction.

In step (b) centrifuging said mixture to yield a first fraction low in cholesterol, the first fraction is suitable for incorporation into a foodstuff. Where wet egg yolk is used as the raw oil in step (a) , in a preferred embodiment the first fraction is a low cholesterol egg yolk product which is then suitable for use, as such, or for mixing with egg white, either for sale as a whole egg product to commercial food processors or for retail sale to homemakers.

In the centrifugation step (b) , in one embodiment a batch centrifugation may be used where a simple test tube is centrifuged for a period of five minutes, during which two discrete phases are reached. An extraction oil phase is decanted off and used in step (c) . The remaining egg yolk is then suitable for further processing as a foodstuff. In a second embodiment, a continuous centrifugation process is used which is more suitable for a commercial operation.

Through the centrifugation process there is a substantially complete separation of the cholesterol from the egg yolk. The cholesterol is uniformly distributed in the oil phase that is decanted off, thereby permitting an optimum removal of cholesterol. The second fraction from step (b) that is decanted off in the centrifugation process is a cholesterol rich oil that is preferably recycled by first treating that fraction under the procedures of step (c) . Step (c) duplicates the procedures of the first aspect of the invention, i.e., it comprises introducing said oil feed at a temperature of at least about 400° F. at an upper portion of a countercurrent thin-film steam stripper while simultaneously introducing steam at a lower portion thereof, wherein said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil, said countercurrent thin-film steam stripper being continuously maintained at a pressure of at least about 1 mmHg and a temperature of at least about 400° F., whereby there is produced a two phase exit flow therefrom comprising a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol.

The vapor phase is rich in cholesterol. It is either discarded or may be retained for recovery of the cholesterol.

The step (d) comprising the recycling of the liquid phase returns the remaining oil for use in step (a) .

In accordance with the second aspect of the Massie Application there is provided an a reduced cholesterol liquid whole egg that comprises (a) egg yolk that contains substantially no cholesterol; (b) an oil substantially free from cholesterol in an amount at least about equal to the amount of cholesterol in a raw egg; and (c) egg white, in an amount substantially equal to the amount of egg white per egg yolk in a native egg. In a preferred embodiment, the oil component (b) is a substantially cholesterol-free oil derived from chicken fat. The following examples illustrate the invention:

EXAMPLE I

In a first stage, virgin fresh or frozen wet egg yolk separated from egg whites by conventional means is mixed with extraction oil at a ratio of two parts of oil per part of yolk by weight. The extraction oil used with the virgin egg yolk is most preferably one recovered from a similar second stage extraction as described in the following step. The mixture is intimately mixed in a low shear, temperature controlled colloid mill for approximately 15 minutes during which time the temperature of the mixture is kept below 130° F and above 90° F and most preferably in the range of 115° F to 125° F. After mixing for 15 minutes, the oil/yolk mixture is centrifuged in a batch or continuous separator to recover a wet, partially cholesterol reduced yolk phase and a cholesterol rich oil phase.

A Fryma VK-7 pilot scale colloid mill is used in this example, equipped with a liquid ring vacuum pump to evacuate the holding tank to approximately 800 millibars of vacuum. Fryma VK- 7 is produced by Fryma-Maschinen AG, CH-4310 Rheinfelden, Switzerland. The colloid mill has a holding tank of 7 liter capacity and the colloid milling head is designed for shear and heat sensitive materials. A water cooled jacket maintains temperature in the mixing vessel below approximately 130° F and most preferably below 125° F.

Separation of egg and oil phases is accomplished using a DeLaval continuous gyrotester disk stack centrifuge operating at 12,000 RPM and equipped with 9.5 millimeter nozzles.

Low shear is obtained by use of a rotor-stator design mixer, in contradistinction to prior art mixing equipment with typical rotation speeds of 7,000 to 25,000 RPM contrasted with the approximately 3,000 RPM of the equipment used in the present invention. The velocity of the agitator tip in the prior art equipment will exceed 200 feet per second, as contrasted with milling equipment with tip speeds of approximately 120 feet per second or less. The Fryma VK-7 is a preferred embodiment of a mixer for use in the present invention that meets the criteria of low shear.

EXAMPLE II

Partially cholesterol reduced egg yolk produced in Example I is mixed with fresh or recovered extraction oil at a ratio of 2 parts of oil per part of egg yolk and mixed in a colloid mill for 15 minutes with temperature controlled below 125° F as in Example I. Following the mixing step, cholesterol reduced egg yolk is recovered from the mixture by centrifugation and the oil phase is recovered for extraction of virgin wet yolk.

EXAMPLE III

Cholesterol rich extraction oil produced in Example I is recovered for reuse by distillation of extraction oil by steam distillation according to the methods described in the Massie Application.

EXAMPLE IV

Following the procedure of Example I, pasteurized egg yolk with a cholesterol concentration of 0.916 % was mixed with fresh soy oil at an oil to egg yolk ration of 2:1 for fifteen minutes at a temperature that held in the range of 90 °F to 115° F and a vacuum of approximately 8000 millibars. The mixture was separated by centrifugation. 3.04 pounds of recovered reduced cholesterol egg yolk fraction was mixed with 6.14 pounds of fresh soy oil, followed by a repetition of the centrifugation process of this example. The cholesterol concentration in the recovered egg yolk fraction was 0.116 % which corresponds to an 87.8 % reduction in cholesterol content.

Accordingly, it is observed that the cholesterol reduction achieved with 4 parts of oil per part of egg yolk under the conditions of this process substantially exceeds the approximately 75 % reduction achieved by Fioriti et al., U.S. Patent 3,717,474, using a comparable amount of oil.

EXAMPLE V

Once extracted egg yolk was extracted with soy oil at an oil to egg ratio of 2.04 to l by milling in a Fryma colloid mill under partial vacuum of 780 millibars and temperatures below 130° F for 15 minutes. Extraction oil containing cholesterol at a concentration of 0.137 % was recovered by centrifugation and immediately mixed with fresh yolk containing cholesterol at a concentration of 1.07 % as before. Egg and oil phases were again separated by centrifugation to yield an oil phase with a cholesterol concentration of 0.515 %.

By calculation it can be shown that the cholesterol concentration resulting from perfect mixing would be 0.512 %. Thus it is seen that reusing extraction oil for a first extraction of fresh, pasteurized or frozen egg yolk does not diminish the mixing efficiency of the extraction.

EXAMPLE VI

A series of extractions were conducted to demonstrate that the extraction efficiency of the oil is not diminished when the oil is recovered by steam distillation of the cholesterol from the edible oil. A further objective of these trials was to evaluate whether there is a build up of artifacts which would adversely affect the organoleptic properties of the yolk.

Soy oil was mixed with fresh or frozen egg yolk at ratios of 2 parts oil to 1 part yolk and mixed by milling in a Fryma colloid mill under partial vacuum of 780 millibars and temperatures held within the range of from 90 °F to 130° F for 15 minutes. Extraction oil was recovered by centrifugation for recovery by steam distillation and the yolk was evaluated for flavor. This process was repeated until the extraction oil had been used 10 times.

During the trial, no off flavors developed in the yolk phase. Under these conditions, perfect mixing would produce a cholesterol reduction of 65 %. While there was some fluctuation during the course of the trial, the final trials showed the same overall reduction as would be predicted using virgin oil.

The observed overall reduction is made more remarkable by the fact that the steam distillation process employed to decholesterolize the extraction oil is known to not remove esterified cholesterol. During the course of the ten trials, esterified cholesterol in the extraction oil gradually accumulated at a rate of about 0.015 % per cycle to a concentration of 0.115 %. Remarkably it has been found that this residual esterified cholesterol does not affect the observed cholesterol reduction in the egg yolk.

EXAMPLE VI

The following example is taken from the Massie Application and describes a general method of use of a continuous process. In the Massie Application, there is described the method of treating a fish oil. In that application, it is described that a commercially obtained menhaden oil was used as the starting material having iodine value of 186, EPA content of 14.6 %, DHA content of 11.2 %, cholesterol level of 0.470 %, and free fatty acid of 0.08 %. A semi-pilot plant oil processing system 10 conforming substantially to FIG. 1 of the aforementioned and incorporated by reference text of U.S. Patent 4,996,072 was utilized to deodorize the above refined fish oil while simultaneously reducing its cholesterol level. The processing system employed a Model No. ESSJ 13-2 Evaporator, steam stripper (available from Artisan Industries, Inc.) as the thin film steam stripping column 30. The processing system was started up by drawing a vacuum on the entire system, heating the pre-evaporator 25 and thin film steam stripping sections 30 using Dowtherm HT, (partially hydrogenated terphenyl) as the heat transfer media, establishing steady state conditions with the stripping steam 15 and 28 in the pre-evaporator 25 and steam stripper sections 30, respectively and charging the system 10 with a continuous feed stream of refined fish oil. The refined fish oil was first deaerated in a feed tank using a vacuum of 25 mmHg absolute pressure and a subsequent nitrogen sparge. Next the feed was pumped through a back pressure valve 12 at a rate of 5.2 lb/hour (2.36 kg/hr) into the processing system, maintained at 1.5 mmHg pressure, where 0.75 lb/hour (0.34 kg/hr) dry steam 15 (14.4 % steam:oil ratio) was sparged in line to form a steam/oil mixture. The mixture was heated in the rising film pre-evaporator section 25, which had 1.96 Ft2 (0.18m2) heating surface area and 550° F. Dowtherm HT circulating in the jacket as heat transfer media 19. The steam/oil mixture achieved a final temperature of about 460° - 480° F. at the top of the pre-evaporator 25, while still at 1.5 mmHg pressure. Next the fish oil/steam mixture flowed into the disengaging chamber or vapor head 16, where the vapor phase was flash vaporized and separated from the liquid phase. The loaded vapor phase 20, consisting primarily of steam with free fatty acids, organic compounds, cholesterol, etc., was drawn to the vacuum system and collected as waste. The liquid phase 22, consisting of par-treated fish oil, was then thin film countercurrent steam stripped in the stripping section 30 which consisted of 13 tube and disc stages which were heated using the Dowtherm HT heat transfer media 32. The oil cascaded over the stages by gravity in a very fine film of a thickness visually measured of about 10 mm, which however in the final stages broke down into a mist of droplets with diameter of 0.2-5 mm. Simultaneously, 0.75 lb/hour (0.34 kg/hr) dry steam (14.4 % steam:oil ratio) 28 was injected at the bottom of the column 30 to countercurrently strip the volatile components from the fish oil, such as free fatty acids, cholesterol, etc. After steam stripping, the oil was immediately cooled to ambient temperature, while still under vacuum, using a small water cooled heat exchanger 36. The fish oil was then collected in nitrogen flushed containers for storage.

EXAMPLE VII

1 part by weight raw egg yolk is mixed together with 2 parts of an extraction oil that has been obtained by subjecting chicken fat to the process of Example VI, whereby the cholesterol content of the chicken fat has been substantially reduced. A wet milling process is used to create an intimate admixture suitable for centrifugation. The wet milling is conducted in an apparatus sold under the trademark, Fryma VK-7 (Fryma-Maschinen AG, CH-4310 Rheinfelden, Switzerland) .

EXAMPLE VIII

A test tube full of the intimately mixed product of Example VII is then centrifuged for a period of five minutes to yield two phases, a lower, egg yolk-rich phase that is retained for processing as a foodstuff, and an upper phase to be decanted off, and used for step (c) . It is understood that in any commercial operation of the present invention, a conventional, continuous centrifugation process is preferably utilized. EXAMPLE IX

The second, cholesterol-rich fraction which is decanted off in the procedure of Example VIII is thereafter introduced as the oil feed of cholesterol which is substituted for the oil containing native cholesterol in the process of Example VI. The resultant two phase exit flow comprises a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol. The vapor phase is discarded, while the liquid phase is recycled to be used as extraction oil for said wet milling.

EXAMPLE X

The lower, egg yolk-rich phase produced in accordance with Example IX that is retained for processing as a foodstuff may be used in a variety of ways. The egg yolk-rich phase may be substituted without further processing for egg yolk in a commercial operation where egg yolk, per se, is required either for cooking or baking.

Where an egg product is to be made available for sale to consumers it is generally reconstituted together with an appropriate amount of egg white to form a whole egg product.

In a preferred embodiment of a reconstituted product, the egg white and the egg yolk-rich phase are mixed together to form a product that is offered to consumers in a "scrambled" form.

Pasteurization is optimally included as a processing step whereby any danger of salmonella or other illness inherent in poultry is obviated. Homogenization is also a desirable processing step.

EXAMPLE XI Instead of creating a "scrambled" egg form as in Example X, it is also possible to form an "egg" in an unscrambled form. The egg-yolk rich phase may be extruded in a conventional manner with pieces of the egg-yolk rich phase being cut into units equivalent to an egg yolk, with the resultant "egg yolk" being treated in conventional means for such reconstitution whereby a solid film encasing the "egg yolk" is formed. A plurality of "egg yolks" is then mixed with egg white under conditions not to break the "egg yolks".

EXAMPLE XII

The "scrambled" form of egg of Example X has an oil content substantially equivalent to that of a regular, untreated egg. Whereas the cholesterol component of the oil has been removed in accordance with the process leading to the egg of Example X, a small amount of oil substantially equivalent to the removed cholesterol is retained. In a preferred embodiment, chicken fat is used as the extraction oil.

EXAMPLE XIII

Instead of providing the replacement oil from the extraction oil in the same amount as the removed cholesterol it is possible to include an excess oil of up to about five percent, and preferably not more than about three percent. In this example, the amount of oil in the "scrambled" egg of the invention of Example 7 is increased by one percent. Inclusion of an increased amount of oil facilitates making a scrambled fried egg food product.

Claims

WHAT IS CLAIMED IS:

1. In the process of removal of cholesterol or fat from an egg yolk fraction through the admixture of said egg yolk fraction with an oil and centrifugation thereof to yield an egg rich lowered cholesterol centrifugate, the improvement which comprises the intimate admixture for a period of at least about three minutes of up to about two parts of edible oil per part by weight said egg yolk fraction under conditions of low shear substantially in the absence of air at a temperature maintained within the range of from about 90° F to up to about 130° F.

2. The process of claim 1 whereby conditions substantially in the absence of air occurs by operation under a partial vacuum.

3. The method of claim 1 wherein said partial vacuum is from about 300 about 1000 millibars.

4. The method of claim 3 wherein said vacuum is from about 500 millibars to about 900 millibars.

5. The method of claim 1 wherein the temperature is controlled to be within the range of from about 115° F to about 125° F.

6. The method of claim 1 wherein said period is at least about five minutes.

7. In the process of removal of cholesterol or fat from an egg-containing mixture which is blended with an oil for a period of at least three minutes that is followed by centrifugation and separation of the cholesterol-reduced egg yolk centrifugate, the improvement which comprises conducting the blending substantially in the absence of air at a temperature of from about 90° F to up to about 130° F.

8. The process of claim 7 whereby conditions substantially in the absence of air occurs by operation under a partial vacuum.

9. The method of claim 8 wherein said partial vacuum is from about 300 about 1000 millibars.

10. The method of claim 9 wherein said vacuum is from about 500 millibars to about 900 millibars.

11. The method of claim 8 wherein the temperature is controlled to be within the range of from about 115° F to about 125° F.

12. The method of claim 8 wherein said period is at least about five minutes.

13. A process for removal of cholesterol or fat from an egg yolk fraction through an at least two stage process of (a) admixing said egg yolk fraction with an oil with said egg yolk fraction substantially in the absence of air for a period of at least three minutes at a temperature of from about 90° F to about 130° F, followed by centrifugation to yield a cholesterol-lowered egg yolk product; and (b) repeating step (a) using said cholesterol-lowered egg yolk product in lieu of said egg yolk fraction, whereby the resultant egg yolk fraction retains the characteristics of egg yolk necessary for baking while having a highly reduced cholesterol content versus that of a raw egg yolk.

14. The process of claim 13 whereby conditions substantially in the absence of air occurs by operation under a partial vacuum.

15. The method of claim 14 which is conducted in two stages.

16. The method of claim 15 wherein said partial vacuum is from about 300 about 1000 millibars.

17. The method of claim 16 wherein said vacuum is from about 500 millibars to about 900 millibars.

18. The method of claim 15 wherein the temperature is controlled to be within the range of from about 115° F to about 125° F.

19. The method of claim 18 wherein, said period is at least about five minutes.

20. In the process for the continuous removal of cholesterol from an egg yolk material which comprises (a) wet milling said egg yolk material having an elevated cholesterol level with an extraction oil whereby there is formed a mixture of the egg yolk material and extraction oil; (b) centrifuging said mixture to yield a first egg yolk-containing fraction low in cholesterol, and a second fraction which is an oil feed having a high level of cholesterol; (c) introducing said oil feed at a temperature of at least about 400° F. at an upper portion of a countercurrent thin-film steam stripper while simultaneously introducing steam at a lower portion thereof, wherein said countercurrent thin film steam stripper is internally configured with sufficient active surface area so that it is capable under appropriate operating flow conditions of temperature, pressure and steam flow rates to remove at least 65 % cholesterol from a cholesterol containing oil, said countercurrent thin-film steam stripper being continuously maintained at a temperature of at least about 400° F., whereby there is produced a two phase exit flow therefrom comprising a liquid phase containing oil with reduced level of cholesterol and a vapor phase rich in cholesterol; (d) and recycling said liquid phase as an extraction oil for said wet milling, the improvement which comprises

wet milling said egg yolk material having an elevated cholesterol level with an extraction oil in step (a) substantially in the absence of air for a period of at least three minutes at a temperature of from about 90° F to about 130° F.

21. The process of claim 20 whereby conditions substantially in the absence of air occurs by operation under a partial vacuum.

22. The method of claim 21 wherein step (c) is conducted at a pressure of at least about 1 mmHg.

23. The method of claim 20 which is conducted under conditions whereby said first egg yolk-containing fraction is suited for incorporation into a foodstuff.