GB2283900A

GB2283900A - Preserving liquid egg

Info

Publication number: GB2283900A
Application number: GB9408376A
Authority: GB
Inventors: Aloysius Knipper
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-11-18
Filing date: 1994-04-26
Publication date: 1995-05-24
Also published as: GB9408376D0; DE4415751A1; CA2121989A1

Description

2283900 is THERMAL ABUSE RESISTANT EGG The present invention relates to

the f ield of enhancing the storage stability of perishable foods.

Liquid egg pasteurized in accordance with minimal pasteurization times and temperatures using a conventional plate heat exchanger may have a refrigerated shelf life of somewhere between about 1 and 2 weeks. Refrigerated shelf life, as the term implies, requires that the liquid egg be properly stored at refrigerated temperatures of under 450F and, preferably, under 40F at substantially all times after pasteurization. If liquid egg pasteurized as described above were left on a counter at room temperature, even in a sealed container, it is unlikely that the liquid egg would remain edible for much longer than about 24 hours. Of course, because the egg is pasteurized, there is no threat of Salmonella infection. However, spoilage microorganisms such as those of the family Bacillaceae and of the family Pseudomonas will grow prodigiously.

As they multiply and grow, the egg is consumed and converted into bacterial waste. As a result, the egg becomes viscous, acidic, and/or rotten smelling as well as unpalatable.

Some, like Dunn et al., U.S. Patent No. 4,695,472, suggest electrically stressing food by the use of high energy, high current density electrical pulses and thereafter, maintaining the electrically stressed food under substantially sterile conditions and packaging so as to have an extended shelf life. Preferably, the electrically stressed foodstuffs are maintained and packaged under aseptic conditions. Dunn et al. suggest that the shelf life of the resulting foodstuff can be improved by adjusting the temperature at which the foodstuff is treated. Further improvement in shelf life may be obtained by cooling the electric field treated liquid foodstuff to a refrigeration temperature of less than 50F. Dunn et al. also illustrate that when liquid egg is heated to 58C (below the temperature necessary for thermal pasteurization of liquid whole egg according to the U.S.D.A.), by use of specific electrical pulses followed by storage at 50F, an increase in refrigerated shelf life is observed.

However, if the treated liquid egg is stored at below 40F, the refrigerated shelf life of the egg extends to 28 days or longer.

others, however, suggest adding various agents to the liquid egg to improve refrigerated shelf life. For example, bacteriocin, nisin, and other antibiotic-like preservatives have been suggested for use in connection with pasteurizing liquid egg so as to provide an extended refrigerated shelf life. For example, as reported in Delves-Broughton et al., OThe use of the bacteriocin, nisin, as a preservative in pasteurized liquid whole eggff, Letters Xn Applied Microbiology, (1992), 15, 133-136, nisin used at levels of 5 mg per liter resulted in a significant increase in refrigerated shelf life of pasteurized liquid whole egg. Nisin also protected liquid egg from the growth of Bacillus cereus.

of course, the suggestion of the addition of nisin to egg is nothing new. For example, Blackburn et al., U.S. Patent No. 5,135,910 discusses the application of nisin compositions as a bacteriocide for treating meats, especially poultry, eggs, cheese and fish and for treatment of food packaging and handling equipment. Blackburn et al.

describe that nisin has been applied effectively as a preservative in dairy products such as processed cheese and that the use of nisin to inhibit the growth of certain gram positive bacteria has been well documented. Blackburn et al. suggest that by the co-administration of nisin and certain chelating or surfactant agents, the growth of gram negative 4 bacteria such as Salmonella tychimux-lum, Eschez-ia coli and others can be controlled and greater activity towards certain gram positive bacteria such as Liste.ria monocytogenes can be realized. See also Blackbux,n et al., U.S. Patent No. 4,980,163 which also suggests the use of nisin and other bacteriocins in conjunction with food such as eggs.

Despite these technological advances in terms of refrigerated storage and extended refrigerated shelf life, consideration of the problems associated with thermal abuse resistance as well as methods of overcoming these problems have remained largely unexplored. It is known that liquid egg that has been pasteurized, placed in an extended shelf life is container and properly stored at 40C or under will last for eight weeks or longer. In fact, an extended refrigerated shelf life of 12 weeks or more is not uncommon. However, it is generally known that as the storage temperature of the liquid egg increases, a decrease in storage life is observed. The inventor has realized that, within limits, for every degree over 40F that liquid egg is stored, one week of extended refrigerated shelf life is compromised. Thus, if extended refrigerated shelf life liquid egg having an anticipated shelf life of 12 weeks is refrigerated at 50OF instead of 400F, the resulting egg should have a shelf lif e of only about 1 to 2 weeks. Thus, a mere 10 change in temperature essentially negates the entire advantage imparted by various extended shelf life pasteurization and packaging techniques. As storage temperatures climb above 500F, the resulting shelf life of the liquid egg is reduced even further to merely a matter of days.

The present inventor has observed that when properly refrigerated and stored, extended refrigerated shelf life egg eventually goes bad and/or when spoilage is brought about by improper filling or contamination during filling, the resulting egg has a dark, almost brownish color. The pH stays approximately the same or, if anything, becomes more basic, and the material smells sour.

In contrast, when egg has been abused by being held at a temperature of above 40"F for any length of time and more particularly, over 45F, the color becomes a bright and uncharacteristically unnatural yellow,, the pH generally drops to as low as 5.5 or below and the product thickens and becomes viscous. Eventually, the material smells rotten. As a result, thermal abuse is a particularly important problem for consumers. While the egg may not smell bad and may not have thickened or discolored sufficiently to alert the consumer, its pH and bacterial content have changed such that the egg should not be used. Often consumers find out about this only after the egg has been incorporated into other products or consumed.

The present inventor believes that, Bacillus cereus and Enterococcus faecalis are difficult to kill by certain pasteurization techniques. When these bacteria remain in liquid egg and the liquid egg is properly stored at 40OF or below, they generally remain dormant. In fact, they may not contribute to spoilage at all. However, when stored at temperatures above 40F, and more often at temperatures higher than 45OF to about 500F, the growth of these difficult-to-kill bacteria becomes extremely rapid. They can then play a profound role in egg spoilage.

Manifestly, the considerations surrounding the problem of thermal storage abuse are extremely different than those involved in extending the refrigerated shelf life of liquid egg. Moreover, while, as before, the attention of the industry was focused on providing methods of imparting an extended refrigerated shelf life, that focus has begun to shift. Egg processors can control the way in which liquid egg is processed and by selecting particular methodologies and by the use of particular types of extended shelf life packaging, can provide the consumer with pasteurized liquid egg having a refrigerated shelf life of 3 months or more. However, processors can only control the quality of the egg so long as the egg remains under their specific control.

once a consumer has purchased the egg, the responsibility for proper handling and refrigerated storage fall upon the consumer. A few days of improper handling, particularly at temperatures approaching room temperature or above, can virtually eliminate all of the extended refrigerated shelf life that technology can provide. Of course, if the egg turns out to have spoiled prematurely,, it is the processor who hears about it and who often must make good even though the reason for the premature spoilage resulted from improper handling and refrigeration on the part of the consumer.

The present invention provides a way to assist processors and users alike in ensuring the continued quality of the liquid egg throughout its intended refrigerated shelf life by providing for various methods of imparting thermal storage abuse resistance to liquid egg products.

It is an object of the present invention to provide liquid egg which is resistant to thermal storage abuse.

It is another object of the present invention to provide liquid egg which will maintain a significant portion of its anticipated extended refrigerated shelf life even after prolonged exposures to improper refrigeration conditions or otherwise elevated temperatures.

It is also an object of the present invention to provide a method for imparting thermal storage abuse resistance to liquid egg.

In accordance with these and other obj ects of the present invention, there is provided a method of imparting thermal storage abuse resistance to liquid egg including the steps of electroheating the liquid egg, holding the electroheated liquid egg for a period of time sufficient to pasteurize the electroheated liquid egg, and adding to the liquid egg at least one antibacterial agent which is effective against gram positive bacteria in an amount which is effective to provide long term abuse resistance to the liquid egg.

As described more fully herein, electroheating and particularly electroheating utilizing high frequency AC electrical energy has is proved to be revolutionary in the pasteurization and processing of liquid egg. By the use of these electroheating techniques, liquid egg can be processed conveniently at both relatively high and relatively low pasteurization temperatures, without electrolysis, without detrimental coagulation and, with a relatively minimal ef fect on the functionality of the resulting egg. Electroheating as described herein provides for an extremely efficacious kill of the microbes contained in liquid egg. Moreover, it has been observed that generally well after pasteurization has been completed, the mortality rate of microbes contained in the liquid egg actually increases. By virtue of the extremely efficacious kill obtained by electroheating as described herein, the relative number of bacteria remaining within liquid egg after treatment is small. It has been found that by adding certain antibacterial agents such as, for example, nisin, to the thus pasteurized liquid egg, thermal storage abuse resistance can be instilled.

Without wishing to be bound by any particular theory of operation, certain spoilage bacteria such as, for example, Bacillus cereus and Ente. rococcus faecalls, may remain in liquid egg after pasteurization. If the pasteurized liquid egg is stored at refrigerated temperatures, and in particular, under 40F, such bacteria are unable to multiply and grow. However, as the temperature of the liquid egg is elevated above 400F, the conditions for growth of these microbes become favorable and their numbers begin to increase. Within limits, as the temperature increases, so too does the rate of growth of these spoilage bacteria. Therefore, if liquid egg is improperly handled or stored, the consequences in terms of compromising the expected refrigerated shelf life of the egg can be significant.

It is believed, however, that if a sufficiently efficacious initial kill can be provided, the addition of nisin or other related antibiotic-like compounds can act together to retard the growth of spoilage microorganisms during the time when the liquid egg is exposed to elevated temperatures.

It is also believed that electroheating provides qualities to the egg which cannot be obtained by other methodologies. Egg treated by electroheating in accordance with the present invention to which bacteriocins such as nisin or other antibiotic compounds have been added is therefore believed to provide particularly efficacious protection against thermal storage abuse.

Moreover, because the electroheating techniques in accordance with the present invention are useful to provide extremely efficacious kill without detrimental coagulation and without a sacrifice of baking functionality, it is possible to achieve the objectives described herein while maintaining a substantially fully functional egg similar in viscosity in baking functionality and in other properties to egg directly out of the shell.

In accordance with another aspect of the present invention, there is also provided a method of storing liquid egg so as to render it resistant to thermal storage abuse which includes the steps of heating liquid egg and holding the liquid egg for -a period of time sufficient to provide an initial average total plate count of 50 or less, adding to the liquid egg at least one antibacterial agent which is effective against gram positive bacteria in an amount which is effective to provide long term storage abuse resistance to the liquid egg and storing the liquid egg at a temperature above 40OF for at least some portion of time. whereby the liquid eggts shelf life is not substantially compromised. Liquid egg resulting from these methods is also contemplated.

Fig. 1 is a schematic representation of one configuration of an electroheating based pasteurization system useful in accordance with the present invention.

The term Oliquid egg in accordance with the present invention is meant to include not only liquid egg white and liquid egg yolk, but also combinations of each in any predetermined or desirable ratio. The term liquid egg" also includes liquid egg white, liquid egg yolk. or combinations thereof (referred to as Oliquid whole egglv) with additives such as salt, sugar, milk, stabilizers, antibiotics, dextrins, cyclodextrins,, peroxides, acids such as citric acid and food including solid or particulate foodstuffs. Liquid egg from which cholesterol has been removed is also included.

The term Oelectroheatingff in accordance with the present invention is meant to encompass a process of generating heat in liquid egg by passing a current through the liquid egg. The liquid egg acts as a resistor and heat is generated thereby. A particularly preferred technique for electroheating food is described in U.S. Patent No. 4,739,140, which is incorporated by reference.

In a more particularly preferred aspect of the present invention, the liquid egg is electroheated -g- is with the apparatus and methods described in a copending application entitled "METHODS AND APPARATUS FOR ELECTROHEATING FOOD EMPLOYING CONCENTRIC ELECTRODESN filed January 22, 1993 having U.S. Serial No. 007, 553. The text of this application is incorporated by reference as is fully set forth herein.

As used herein, the terms 'pasteurization', Npasteurizel and NpasteurizedO refer to the killing of sufficient pathogenic microorganisms contained within food and in particular liquid egg so as to render the food edible without threat of, for example, salmonella infection. OPasteurizationff may also be thought of as a treatment which is designed to eliminate, for all practical purposes, pathogenic micro-organisms and, in particular, salmonella, and, secondarily, to reduce the number of spoilage microorganisms present to improve the keeping quality of the food product. At U.S.D.A. minimum time and temperature parameters, pasteurization will generally produce liquid egg which will have a refrigerated shelf life of between about 7 and about 14 days. For liquid whole egg, a minimum temperature of 140OF and minimum holding time of 3.5 minutes is required. The definition of pasteurization, in terms of attained temperatures and holding times, for other foods is generally provided by government regulation and industry standards. They are therefore readily acceptable.

"Extended refrigerated shelf lifeff means that the liquid egg is safe to consume for a period of at least 3 weeks after treatment in accordance with the present invention. This, of course, assumes proper refrigerated storage. Preferably, the term Nextended refrigerated shelf lifeN means that the liquid egg is safe to consume for a period of at least 4 weeks after treatment in accordance with the present invention and more often 10 to 12 weeks after treatment, or longer. An extended refrigerated shelf life can also be imparted to other perishable foods by the practice of the present invention.

NElectrolysisO refers to a chemical process which can take one of at least two forms. one form of electrolysis results in the dissolution of the metal electrodes inserted into the food being treated. As electrons flow between the pair of electrodes, the metal within the electrodes becomes ionized, thereby releasing electrons. The ions are soluble and dissolve into the food being treated. Another electrolytic problem is caused by the conversion of conductive ionic species within the food being treated to radicals and gases, such as the conversion of a hydrogen ion to hydrogen gas and chlorine ions to chlorine gas. Hydroxide ions can subsequently be converted to water and oxygen. This conversion can adversely impact the flavor and other advantageous qualities of the treated food both as a result of the direct depletion of ions and their conversion to other species and by initiating other reactions within the food such as oxidation.

Coagulation generally involves the denaturation and agglomeration of protein contained in a food. Some foods, like, orange juice, do not coagulate when heated. other foods, such as liquid egg, do coagulate when a sufficient amount of energy is applied.

In accordance with the present invention as it relates to liquid egg and other coagulable foods, coagulation is usually to be minimized. At certain pasteurization temperatures, for liquid egg, some degree of coagulation will occur. However, in accordance with the present invention, and unless the liquid egg is to be cooked, Odetrimental coagulationg should be prevented. Detrimental coagulation is an increase in the viscosity of the liquid food such that its smooth pourable nature is compromised. Its is functionality is also compromised at this point and visible particles of egg appear.

The term mantibacterial agent' in accordance with the present invention includes any antibiotic agent which is effective against gran positive bacteria. More particularly, however, it refers to bacteriocins such as, for example, nisin, epiderman, cinnamycin, duramycin, ancovenin, Pep 5, tylosin, and subtilin. These compounds may, of course, also be effective in controlling some forms of gram negative bacteria.

The term retained baking functionality" means that despite the application of heat in accordance with the present invention, the liquid egg is useful for most commercial and home, if not all, baking applications. Baking functionality relates primarily to the emulsification properties of the liquid egg. This function directly relates to the stability of water/oil, water/air, oil/air, or water/oil/air phases. Emulsifications influence the viscosity of the batter, volume of the baked goods and stability thereof. The stability of a two or three phase system also greatly affects the texture of the resulting baked product. In a cake, a desirable soft uniform crumb can be achieved only with the proper emulsification system. In fact, the quality of certain baked goods, such as, for example, sponge cake, is considered wholly dependent upon the quality of the egg used. Good egg product, that is one having high baking functionality, yields high volume and soft texture.

Thermal abuse" in the context of the present invention involves the exposure of liquid egg which is intended to be stored under refrigerated condition to temperatures of over 40F and, in particular. 50F or over for a time which is sufficient for the liquid eggst temperature to begin to rise. Thermal abuse can occur in many forms, such as when a refrigeration unit is inadequate to provide proper refrigerated storage. For example, -in convenience stores, refrigeration space is usually at a premium. Often, because of the relatively high turnover, products which should be refrigerated are kept in a cold room adjacent actual refrigerated storage units. In supermarkets, eggs and other dairy products are traditionally sold in open refrigerated racks or cases. The temperature of the material contained within packages in these cases can depend on the ambient temperature of the store, the proximity of the package to the front of the rack and whether or not the package is in direct contact with a refrigerated shelf or is merely stacked upon other containers.

Thermal abuse may also occur, or may be compounded, when a consumer removes a poorly refrigerated package from such an open refrigerated case and places the refrigerated product in a shopping cart early in an extensive shopping trip. The refrigerated product may therefore be exposed to ambient temperature conditions for up to several hours until the package is taken home and placed into a refrigerator.

Thermal abuse can also occur during normal shipping and handling. For example, the refrigeration unit on a refrigerated truck or boxcar can break during transit, thereby exposing the packages and their contents to elevated temperatures for a prolonged period of time. In addition, during the shipping process, containers may wait on a loading dock for several hours either prior to being loaded onto a truck or thereafter.

In accordance with the present invention, Othermal abuse resistancem can be imparted to liquid egg. In the broadest sense, vthermal abuse resistanceO in accordance with the present invention means that liquid egg processed in accordance with the present invention which has been thermally abused will retain a substantially greater portion of its intended refrigerated shelf life than would liquid egg which has been merely pasteurized under identical conditions and thermally abused to the same extent. For example, egg pasteurized and packaged under identical conditions and exposed to the same degree of thermal abuse,, will last longer. Preferably, liquid egg so treated in accordance with the present invention will have at least one day's longer shelf life. Of course, the lesser the degree of thermal abuse, i.e. exposure to lower temperatures for shorter periods of time, the less severe the impact of the exposure. Therefore, by the practice of the present invention, it may be possible to negate entirely the effects of such minimal abuse and/or allow the liquid egg to retain a much larger percentage of its extended refrigerated shelf life. Thus, for example, liquid egg stored at 45OF which might be expected to have its refrigerated shelf life reduced from 12 weeks to 7 weeks, might last for 8 weeks or longer. In addition, the use of electroheating and, for example, nisin, in accordance with the present invention, allows the processor to realize not only a low total plate count and thermal abuse resistance, but also a higher level of retained baking functionality with little or no detrimental coagulation. This is especially true when the liquid egg of the present invention is compared to egg processed by other methods to yield the same plate count.

The methods of the present invention will be better understood with reference to the schematic diagram of Fig. 1, which describes a typical device used for pasteurizing liquid egg products. This typical egg pasteurizer has, however, been modified by substitution of an electroheater 71 where a plate heat exchanger or other conventional heating device could be used. This and similar devices can also be used in -14 connection with the heat treatment of a wide variety of foods.

As shown in Fig. 1, and for illustrative purposes only, liquid whole eggj' usually in refrigerated form, is transferred from a holding tank 1 to a balance tank 2. Liquid egg could also be introduced into the apparatus directly from a tank car,, tank truck or from an egg breaking line.

Thereafter, the liquid whole egg is pumped through a timing pump 3 which keeps the liquid whole egg moving throughout the entire pasteurization apparatus. The liquid whole egg is then preferably preheated by any conventional means of heating such as ovens, vats and/or steam infusion systems. In addition, electroheating elements or cells of the present invention can also be used to preheat the liquid whole egg. The liquid whole egg is usually brought from refrigerated or room temperature up to about 1390F or higher. More preferably, however, a conventional plate heat exchanger 4 is used to accomplish preheating.

As shown in Fig. 1, the regeneration section 5 of a conventional plate heat exchanger 4 is connected to the output of timing pump 3. The liquid whole egg temperature is raised in the regeneration section 5 from, for example, 350-400F to between about 90F and about 1200F. Thereafter, the liquid whole egg is introduced into the heating section 6 of plate heat exchanger 4 for further preheating. In heating section 6 the temperature of the liquid whole egg is further elevated in temperature to something below pasteurization temperature, usually between about 120OF and about 149F. In a preferred embodiment, preheating temperatures of about 123F and about 149F and more preferably between about 130OF and about 1440F are used for liquid whole egg. Unless relatively high pasteurization temperatures are used, it is generally preferable that the maximum preheating is temperature be selected such that it is below the pasteurization temperature of the particular f orm of food being treated. In the context of liquid whole egg, preheating temperatures generally range up to about 139F.

Thereafter, the liquid whole egg passes between the electrodes of an electroheater V. The electroheater 71 is supplied with a high frequency AC electric current which is effective to heat the liquid whole egg without electrolysis. Preferably, the AC electric current has a frequency above about 100 Hz and, more preferably, above about 100 kHz. Most preferably, frequency used ranges from between about 150 kHz and about 450 kHz. This energy is applied to the liquid whole egg in such a way so as to avoid detrimental coagulation. In electroheater 7 4' the temperature of the liquid whole egg is elevated from its preheated temperature to the desired pasteurizing temperature. Pasteurization temperatures in excess of 170OF for liquid whole egg can be achieved, however, preferred pasteurization temperatures of between about 1400F and about 165OF and more preferably, between about 140OF and about 1550F are achieved. Most preferably, pasteurization temperatures between about 140OF and These temperatures are, of course, for liquid whole egg only. For liquid egg white, temperatures should range from between about 1240F (with peroxide) or about 134F (without peroxide) to about 139F.

After being electroheated, the liquid whole egg is then passed through holding tubes 8 where it is held for a period of time sufficient to complete pasteurization in accordance with the Federal Regulations. Generally, holding times of between about 0.1 seconds and about 5 minutes can be used, however, times of between about 2 and about 4 minutes are preferred. The liquid whole egg then passes to about 145F are used.

flow diversion valve 9. If the temperature of the liquid whole egg exiting holding tubes 8 is below-a preset value the liquid whole egg is returned to the balance tank 2 to go through another pasteurization pass. If, however, the exit temperature is at or above the preset value, the liquid whole egg is allowed to proceed via the cooling means 10 to the packager 11, or to a holding tank, tank car, etc.

When cooled by cooling means 10, the pasteurized electroheated liquid whole egg preferably returns to a refrigerated temperature of between about 32F and 45F.

Cooling means 10 can be any device useful for lowering the temperature of the electroheated liquid egg, liquid whole egg in this case, quicklyenough to avoid detrimental coagulation. When high temperatures, and in particular, temperatures over about 1556F to 160"F and higher are reached during pasteurization, the need to rapidly cool the liquid whole egg becomes acute. In such cases it may be necessary to utilize a 'Yff-shaped cooling device such as described in the aforementioned U.S. Patent Application No. 07/862,198, filed on April 2, 1992.

When, however, pasteurization temperatures are below 160OF and more particularly below 155F, it is acceptable to use more conventional cooling means 101 such as the cooling/regeneration section and refrigeration section of a conventional plate heat exchanger. In fact,, cooling means 101 may be the cooling/regeneration and refrigeration sections 14 and 16 respectively, of plate heat exchanger 4, as shown in dashed lines in Fig. 1. In that case ' after leaving flow diversion valve 9, the electroheated liquid whole egg would flow into the cooling/regeneration section 14 of plate heat exchanger 4 via conduit or pipe 12 where its temperature would be lowered to between about 120F and about 600F. Thereafter, the cooled liquid whole shelf life and egg would be refrigerated in the refrigeration section 16 of heat exchanger 4 where its temperature would be lowered to between about 320F and about 45F and, more preferably, between about 32F and about 400F. Thereafter, the refrigerated liquid whole egg could be stored, loaded into a tank car or truck or packaged in packaging device or packager 11.

Packaging device 11 need not be aseptic. By electroheating and storage at 40OF or under, it is not necessary to aseptically package processed pasteurized liquid egg in order to obtain an extended refrigerated more particularly, an extended refrigerated shelf life of eight weeks or more. Aseptic packaging procedures are described in 21 C.F.R. 113.3, 114.40(g) and 113. 100 (a) (4). Generally during aseptic processing, a commercially sterilized product is introduced into a sterile package under sterile conditions such that the filling and sealing of the package is all conducted in a sterile environment. of course, liquid egg in accordance with the present invention and the majority of known technology is not sterile. Nonetheless, aseptic packaging procedures insure that a statistically insignificant number of cells are introduced during packaging. For purposes of illustration only, aseptic packaging should introduce approximately one cell per 1,000,000 packages. Aseptic packaging can be accomplished using an International Paper Model SA aseptic packager or a Scholle Model 10-2E aseptic packager. Of course, aseptic packaging may be utilized in accordance with the present invention. However, because of the present invention, it need not be.

Another type of packaging useful in accordance with the present invention is the so-called "clean pack" which may be produced using a Cherry Burrell packager Model EQ3 or EQ4. This type of packaging has a higher failure rate or, more correctly -is- is put, a higher incidence of the introduction of microorganisms during packaging than a truly aseptic system. For illustration purposes only, a clean pack may introduce one cell per every 100,000 packages.

While the use of this packaging technology does not qualify as aseptic, it is certainly acceptable in terms of the present invention and such devices may be used as packaging device 11. These Cherry-Burrell packages can also be run so as to produce plain sanitized clean containers as discussed below. For example, if the packages are not treated with a peroxide spray prior to filling, they can be considered sanitized, but not aseptic or Oclean packs." These are both forms of extended refrigerated shelf life packages.

Also useful in accordance with the present invention are plain sanitized clean containers produced and sanitized using Ogood manufacturing proceduresO in accordance with all government regulations. Such containers which have been properly sanitized may introduce as many as, for illustration purposes only, one cell per hundred packages. Because of the superior kill provided by electroheating and the growth inhibitory effect of proper refrigerated storage, such an addition of cells is not considered significant.

These aforementioned packages, which are all specifically useful in practicing the present invention to provide extended shelf life, may be contrasted with a Ndirty packageN which has not been sanitized nor packaged under clean or aseptic conditions. Such containers may introduce 1,000 cells per package or more which is statistically significant relative to the number of cells remaining in pasteurized liquid egg after successful pasteurization. Any other type of package can be utilized, as individual customers may require. Of course, the introduction of any microorganisms after

3 treatment is to be avoided at all costs. However, the packaging processes described herein do not significantly increase the total plate count and, therefore. should not affect refrigerated shelf life.

With this overview in mind, the various aspects of the present invention will now be described.

In accordance with the present invention, sufficient antibacterial agent is added to the liquid egg so as to provide long term thermal abuse resistance thereto. If, for example, nisin is added prior to pasteurization, there is some evidence that it will also assist in providing a more efficacious pasteurization. However,, the amount of nisin remaining within the resulting liquid egg may be reduced,, thereby compromising the degree of thermal Therefore, it other abuse resistance which may be imparted. be advantaaeous to add nisin may or antibacterial agents in accordance with the present invention to the liquid egg after pasteurization. However, it is also possible to pasteurize liquid egg using, for example, nisin and then augment the nisin content of the egg after pasteurization.

The amount of antibacterial agent useful in accordance with the present invention can vary widely depending upon the extent of the initial kill of microbes provided by pasteurization, the relative chance of thermal storage abuse, the degree and extent of anticipated thermal storage abuse, the particular antibacterial agent or agents used and the anticipated extended refrigerated shelf life of the resulting liquid egg. For nisin, an amount of at least about 0.75 ng/kg of liquid whole egg should be used. More preferably, between about 1.25 mg/kg and about 250 ng/kg of nisin may be used. The amounts of other antibacterial agents can be adjusted so as to provide a level of efficacy substantially corresponding to the useful levels of nisin.

is The efficacy of the addition of such antibacterial agents may be enhanced by the addition of a chelating agent or a surfactant agent as described in U.S. Patent No. 5,135,910, the text of which is incorporated by reference. Chelating agents used in accordance with the present invention may include EDTA, CaEDTA, CaNa2EDTA, and other alkyldlamine tetraacetates, , EGTA, citric acid, and citrate. Surfactants as described herein may include tweens, tritons,, glycerides,, fatty acids, quaternary compounds, sodium dodecyl sulphate and cocamido propyl betaine. These can be present in an amount of between about 0.1 mM to 20 M In addition. it is also known that compounds such as nisin can be used in combination with glycanohydrolases to provide particularly efficacious kills during pasteurization. It is believed that the coaction of these various agents, such as lysozyme, will also be efficacious in providing enhanced thermal abuse resistance. Lysozyme, for example, may be added in an amount of between 0.1% and about 1.0% by weight.

These additional ingredients may be added before, during or after pasteurization. They may be added with the antibacterial agent or separately. If added before pasteurization, it may also be desirable to augment these materials as they may be digested during heating.

Consistent with the belief that the combination of a particularly efficacious kill and the use of an antibiotic agent such as, for example, nisin, can provide significant thermal abuse resistance during storage. a preferred aspect of the present invention involves electroheating the liquid egg as previously described such that the total initial plate count of the liquid egg is under about 50. However, the liquid egg must be treated in such a way that its baking functionality is substantially retained and the detrimental coagulation attendant certain pasteurization processes is minimized. Thus higher temperature techniques such as those disclosed in Jones et al., U.S. Patent No. 3,113,872, and Swartzel et al., U.S. Patent No. 4,808,425, are generally contraindicated. Of course, such techniques may be useful in accordance with the present invention. However, they are believed to be unable to provide the extremely efficacious kill with little or no sacrifice in terms of detrimental coagulation and baking functionality as called for in this aspect of the present invention.

In accordance with this preferred aspect of the present invention, liquid egg is electroheated, with or without the addition of nisin, to a temperature of between about 140OF and about 145F and is held at that temperature for approximately 3.5 minutes. Thereafter, nisin or other similar agents may be added and the product is packaged and stored under refrigerated conditions. Preferably, a storage temperature of 40OF or below is maintained. If the resulting package liquid egg is stored improperly for any length of time, the combination of the particularly low kill and the antibacterial agent such as nisin should provide significant protection against spoilage.

The foregoing will be better understood with reference to the following examples. These examples are for purposes of illustration. They are not to be considered limiting as to the scope and nature of the present invention. VxgaRle I six two pound gable top containers containing liquid whole egg electroheated to a temperature of 1470F and held at that temperature for approximately 3 1/2 minutes were removed from a processing run. The liquid egg was packaged using a Cherry-Burrell model EQ3 packager which provides for a so-called ffclean packO. The liquid whole egg included citric acid in an amount which was insuf f icient to provide any preservative effect but was useful for stabilizing the color of the egg yolk. The treated liquid egg has an approved ten week refrigerated shelf life. 200 milligrams of NISAPLIN, available from Barrett Ltd. Trowbridge, Wilts, England BA148TR, in solution was injected through the container using a sterile syringe. one milligram of NISAPLIN contains about 0.026 milligrams of nisin, i.e., NISAPLIN is about 1/40th nisin by weight. Thereafter, the introduction hole was taped shut. Four of the six containers were treated in this way. The remaining two containers were used as a control. Each of these were punctured with a sterile syringe and thereafter were taped shut. The six containers were then stored in a windowless room at an ambient temperature which ranged from between about 68F and about 750F.

Four days after treatment both of the controls had turned sour. They were characterized by strong smell, high viscosity, and uncharacteristically bright yellow color. The plate counts were too high to measure. The liquid egg in two of the four test containers had begun to show some signs of thickening. The plate counts for these two samples were also too high to measure. However, they did not have an objectionable smell. By standard observation, it was believed that these containers included egg which was safe for consumption at that moment. However, there was at least a 50% chance that the egg would become inedible within 24 to 48 hours.

The remaining two samples of egg treated in accordance with the present invention showed no signs of thickening, discoloration or other physical change. The egg contained in these second two containers did not include an objectionable smell and tasted fresh and sweet. Total plate counts of 500 and 600 were observed.

The electroheated liquid egg in accordance with Example 1, when stored at room temperature between 2 and 3 days, turned sour and spoiled.

However,, by the use of nisin in accordance with the present invention, the liquid egg was still safe to consume and palatable for 4 to 5 days or longer. This represents almost a 100% increase in the shelf life of the liquid egg even over egg which had been electroheated. Liquid egg treated by conventional plate heat exchangers, for example, at 1470F or so would be unlikely to last for more than I to 2 days before spoiling. Thus the practice of the present invention including both electroheating to provide a particularly efficacious kill in combination with an antibacterial agent such as nisin can provide a significant increase in storage stability over conventionally pasteurized egg.

This rather rigorous test exemplifies the advantages of the present invention when liquid egg is -----ZO---rtored on a countertop at room temperature. Of course, if liquid egg was merely stored under improper refrigeration conditions such as, at between about 459F and 500F, the extended refrigerated shelf life of the liquid egg would not be reduced to only 5 or more days. Under such conditions, particularly if the improper storage does not persist, the extended refrigerated shelf life of the egg may be significantly retained so that the liquid egg may be stored for as much as 6 to 8 weeks or more.

Example 2

The six containers described in Example 1 were resealed and held at room temperature for four additional days. When the two control containers were opened, a strongly rotten odor was given off. Visible colonies of bacteria were present in the egg and the egg had noticeably thickened and darkened in color. The four cartons containing electroheated liquid whole egg and nisin had also become thick and turned sour.

The pH of all six containers was about 5.3. In addition, while a sour fermentative odor was detected, the rotten odor normally associated with egg turning bad was not noticeable.

Emmule - 3 Six additional containers of liquid egg as described in Example 1 were prepared and stored. 300 mg of NISAPLIN was introduced into two containers, 400 mg of NISAPLIN was introduced into two containers and 500 mg of NISAPLIN was introduced into the last two containers. The four containers including 300 and 400 mg of NISAPLIN were observed to be thick, their color had changed, and a sour odor was present. The pH of the samples was about 5.45. The two containers including 500 mg of NISAPLIN, however, were perfect in terms of color and viscosity. Their smell was sweet and their viscosity was about 6.75. The six containers were stored for eight days at room temperature of between about 68F and about 750F.

Zzg%Rle 4 Ten thousand pounds of TABLE READY brand liquid whole egg from Papetti's Hygrade Egg Products, Inc. of Elizabeth, New Jersey were pasteurized by electroheating at a temperature of approximately 143F and held at that temperature for approximately three and a half minutes. The liquid egg was packaged using a Cherry-Burrell Model EQ3 Packager which provides for so-called OClean PacksO. Three pounds of NISAPLIN was dissolved in forty pounds of water and introduced into the liquid whole egg while the egg was in the holding tank prior to pasteurization. After processing the containers, including liquid whole egg pasteurized in the presence of nisin, were stored at either 40F or 500F, both of which can broadly be considered ffrefrigerated' temperatures. Controls consisting of TABLE READY liquid whole egg were processed and packaged under the same conditions as described herein, without the addition of NISAPLIN. The controls were actually processed a day before the KISAPLIN containing samples. The amount of NISAPLIN used equated to approximately 7.8 mg. per ounce or 27.5 mg. per hundred grams of liquid whole egg.

The amount of nisin thereby delivered was approximately 0.20 mg. per ounce or approximately 0.68 mg. per hundred grams. The results are reported in Table I.

TABLE I (Hisin was added before pasteurization) SAMPLE 0 1 2 3 4 5 6 7 a 9 10 40OF SAMPLE 10 60 LT 100 200 LT 100 LT 100 LT 100 LT 10 100 LT 100 LT 100 4" is CONTROL 10 LT 100 LT 100 LT 100 LT loo LT loc LT 100 LT loc 11,500 150, 000 TNTC 50OF SAMPLE 10 LT 100 20 LT 100 LT 100 LT loc LT 100 LT loc 8,900 THTC THTC 50OF CO)MOL 1 LT 100 LT 100 TNTC TNTC TNTC THTC THTC THTC THTC LEVELS USED: NISAPLIN: 7.8 agloz. LT- Less Than 27.5 ag/100 g TNTC - Too Numerous to Count NISIN: 0.20 =gloz.

0.68 ag/100 g At 40F, the controls exhibited a significant increase in total plate count between the seventh and eighth week. By the ninth week, the samples opened were no longer consumable. In contrast. the sample containing NISAPLIN continued to have acceptable total plate counts for a full ten weeks.

The liquid egg stored at 50'F, without NISAPLIN, lasted approximately two weeks bef ore the total plate count increased to the point where the number of bacteria were too numerous to count. In contrast, liquid egg processed according to the present invention, including NISAPLIN, did not exhibit a significant increase in total plate count until Week 8 at which point, the liquid egg was still consumable.

This test underscores not only the importance of the discovery of the present invention, but also the unexpected nature of that discovery. As previously described, it has been reported that nisin used at levels of 5 mg. per liter resulted in an increase in refrigerated shelf life of pasteurized liquid whole egg. Indeed, as exemplified by the samples stored at 40, the use of nisin, particularly in combination with electroheating, can provide an enhanced and extended refrigerated shelf life. Of course, it should be noted that without the use of electroheating (as was the case in the reported literature), the shelf life of the pasteurized liquid egg,, both with and without nisin was considerably shorter than exemplified herein. However, when stored at 50F, a significant and unexpected difference in the keeping qualities of the liquid egg was observed.

Electroheated liquid egg having an extended refrigerated shelf life by virtue of the electroheating process alone spoiled in under three weeks. If properly stored, electroheated liquid egg would be expected to have an extended refrigerated shelf life of B-10 weeks. With the addition of nisin, however, the liquid whole egg retained most of the predicted shelf life lasting between eight and nine weeks prior to spoilage. Such a profound difference in abuse resistance could not have been predicted based upon the effects of nisin on extending refrigerated shelf life.

ZZM210 S Liquid egg was processed and prepared as described in Example 1 with 7.8 mg. per ounce of NISAPLIN being injected into the already processed egg sealed within a container using a sterile syringe.

The resulting containers were stored at 50F and tested as previously described. Initial testing of the liquid egg exhibited a total plate count of 10. A second container was opened at the end of Week 1, and I.

the total plate count again was less than 10. A third container was opened at the end of the second week, and the total plate count was 30. A fourth container was opened at the end of three weeks, and the total plate count was less than 10. After four weeks, another sample was tested, and the total plate count was 360. Samples were also tested at Weeks 5, 6, 7, 8, 9 and 10. However, in each case, the total plate count was too numerous to count. This shows that particularly unexpected results are obtainable by the use of nisin, prior to pasteurization, in combination with electroheating.

Example 6

Additional containers of TABLE READY brand liquid whole egg were prepared as described in Examples 1 and 5. However, into each, NISAPLIN in the amount of 15.6 mg. per ounce or 55.0 mg. per hundred grams was injected. The initial total plate count was 10. The plate count after one week was 10. After the second and third weeks, the total plate count was less than 10. After four weeks, the total plate count was 10. Individual samples checked in Weeks 5 and 6, however, had plate counts that were too numerous to count. These last two examples illustrate that nisin is useful, both before and after pasteurization, and at levels quite unexpected over the art.

The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular embodiments disclosed, since these are to be regarded illustrative rather than restrictive. Variations and changes may be made by others without departing from the spirit and scope of the invention.

is

Claims

CLAIMS:

1, A mcthgd of imparting thermal stora.ge abuse resistance to liquid egg comprising electroheating said liquid egg (7, 711) and holding raid electroheated liquid egg (8) for a period of time sufficient to pasteurize said electroheated liquid egg. characterized by adding to said liquid egg at least one antibacterial agent which is effective against gran positive bacteria in an amount which is effective to provide thermal abuse resistance to said liquid egg.

2. The method according to claim 1, characterized in that said antibacterial agent is added prior to the step of electroheating (7, 70) said liquid egg.

3. The method according to claim 1 or 2, characterized in that said antibacterial agent is nisin, and is added in an amount of at least about 0.75 mg/kg of said liquid egg.

4. The method according to claim 3, characterized in that said nisin is added in an amount of at least about 1.25 mg/kg of said liquid egg.

5. The method according to claim 4, characterized in that said nisin is added in an amount of between about 1.25 and about 250 mg/kg of said liquid egg.

6. The method according to claim 1, further characterized by adding to said liquid egg and said antibacterial agent at least one edible chelating agent, at least one edible surfactant or at least one glycanohydrolase.

7. The method according to claim 6, characterized in that said edible chelating agent is selected from the group consisting of EDTA, CaEDTA, CaNa2EDTA, and other alkyldiamine tetraacetates, EGTA, citric acid, and citrate.

8. The method according to claim 6, characterized in that said surfactants are selected 1 from the group consisting of tweens, tritons, glycerides, fatty acids, quaternary compounds, sodium dodecyl sulphate and cocamido propyl betaine.

9. The method according to claim 6, characterized in that said glyonohydrolase is lysozyme.

10. A method of storing liquid egg which has been rendered resistant to thermo storage abuse comprising providing the liquid egg and electroheating said liquid egg (7, 7,w), characterized by adding an antibacterial agent to said liquid egg which is effective against gran positive bacteria in an amount of at least about 0.75 mg/kg of said liquid egg, electroheating said liquid egg (7, 70) and holding said liquid egg (8) for a period of time sufficient to provide an initial average total plate count of 50 or less, and storing said liquid egg (11) at a temperature above 40F for at least some portion of time.

11. The method according to claim 10, characterized in that said antibacterial agent is nisin.

12. The method according to claim 11, characterized in that said nisin is added in an amount of at least about 1.25 mg/kg of said liquid egg.

13. The method according to claim 12, characterized in that said nisin is added in an amount of between about 1.25 and about 250 mg/kg of said liquid egg.

14. The method according to claim 10, 11, or 12, further characterized by adding to said liquid egg and said antibacterial agent at least one edible chelating agent, at least one edible surfactant or at least one glycanohydrolase.

15. A method of imparting thermal storage abuse resistance to liquid egg comprising electroheating said liquid egg (7, 711) characterized by adding to said liquid egg at least one antibacterial agent which is effective against gram positive bacteria in an amount which is effective to provide thermal abuse resistance to said liquid egg, and electroheating said liquid egg (7, 70) and holding said liquid egg (8) for a period of time sufficient to provide an initial average total plate count of 50 or less, under conditions which will minimize detrimental coagulation and maximize retained baking functionality.

16. The method according to claim 15, characterized in that said antibacterial agent is nisin and is added in an amount of at least about 0.75 ing/kg of said liquid egg.

17. The method according to claim 16, characterized in that said nisin is added in an amount of at least about at 1.25 ng/kg of said liquid egg.

18. The method according to claim 17, characterized in that said nisin is added in an amount of between about 1. 25 and about 250 mg/kg of said liquid egg.

19. The method according to claim 15, 16, or 17, further characterized by the step of adding to said liquid egg and said antibacterial agent at least one edible chelating agent, at least one edible surfactant or at least one glycanohydrolase.