CA2089933A1

CA2089933A1 - Methods and apparatus of electroheating liquid egg

Info

Publication number: CA2089933A1
Application number: CA002089933A
Authority: CA
Inventors: David Reznik; Aloysius Knipper
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-04-02
Filing date: 1993-02-19
Publication date: 1993-10-03
Also published as: US5290583A; DE4310753A1; GB9305118D0; US5670198A; US5415882A; US5533441A; GB2265538B; GB2265538A

Abstract

ABSTRACT OF THE DISCLOSURE
Provided herein is a method for electroheating liquid egg. Also provided herein is an apparatus specifically designed for heating and cooling materials and preferably liquid egg and apparatus for pasteurizing liquid egg by electroheating.

Description

208~933 ODS A~D_AP~ARAT~ OF_EL~C~RO~A~IN~ ~IQ~ GG
The present invention relate6 to methods and apparatus for el~troheating, processing, pasteurizing, and/or cooking liquid egg.
S There are a number of techniques which are known for pasteuriæing and procQssing liquid egg. The more popular approaches involve the use of convention~l plate heat exchanger~, steam infusion sy~te~s, or Gombinations of both~ ~owev~r, the~e tech~iques have li~itations because of the physical nature of liquid ~gg. Plate h~at exchangers are very popular in that they are very efficient and relatively simple to use.
However, plate heat exchangers are limited in the amount of heat that they can convey to liquid eggs without causing irreparable harm such a~ undue ooagulation, scorching, caking on the plate, and the like.
Furthermore, the highest effective temperature range over which heating can be accomplished by plate heat exchangers is limited to between about 150-F to about 155 F, particularly for long term, continuous processing techniques. As a matter of practical reality, plate ~eat exchangexs can only be used to heat liquid whole egg to pasteurization temperatures of between about 140DF and about 155-F for an extended period of time.
Steam infusio~ systems can be used to obtain much higher temperatures such as, for example, 16SF.
However, it is necessary to separate the condensed steam and residual water from the liquid egg during processing. The equipme~t used for steam pasteurizing liquid eggs is also quite expensive and elaborate.
-I-t is of course possible to pasteurize at lower te~peratures without the attendant sh~rtcomings of high temperature metbodologie~. Howev~r, in so doing, sacrifice are made in ter~ of the degree of microbial kili and extent of the storage stability of the resulting liquid egg product.

2~993~

Electroheating ha~ been used successfully for the heat treatment, and principally the cooking, of food stuff6. A particularly important technique for electroheating is described by Mr. David Reznik, (a CG inventor hereof) in U.S. Patent No. 4,739,140, the entirety of which is hereby incorporated by reference.
Mr. Reznik found that when an AC electric current at a freg~ency exceeding mains frequenoy is passed through food, heating of the food can be accsmpli~hed without substantial electrolysiE or reaction between the fo~d product and the electrodes.
Mr. Reznik's '140 patent does not describe, however, pasteurizing egq. ~urther~ore, this important work does not discuss any of the uni~ue qualities or unique problems associated with the continuous pasteurization of liguid egg. Liquid egg is unique and when considering its preparation, processing and/or storage a nu~ber of often competing criteria must be taken into account, including, without limitation:
storaye stability, content of potentially pathogenic bacteria, foaming ability, emulsion properties, viscosity, detrimental coagulation, and pourability.
Largely because of this complexity and because of practical commercial considerations, the application of Mr. Reznik's original discovery to continuous liquid egg pasteurization was not without difficulty. Originally, such problems as caking on one or the other electrode (particularly at low frequency), detrimental coagulation, odor, and arcing, were observed. The reasons for these problems are not yet completely understood. However, the interplay of the demands of regulatory-~ oversight, commercial desirability, the qualities and properties of liquid egg, and the physical constraints of the original electroheating appara~us design are most likely re6ponsible.
U~S. Patent No. 4,695~472, (the ~'472 patent~l discuss~s methods and apparatus ~or extending the shelf life of fluid food products including eggs. ~he ~ethods ~8~933 and apparatu~ described involve the repea~ed application o~ high voltage, high current density, discrete electrio pulse~ to fluid food products~ Field strengths used are, at a mini~um, 5,000 volts/cm, Y~ltages as high as, for example, 37,128 volts are disclosed. Current densities o$ at lea~t about 12 amps/cm2 are also disclosed as are pulse frequencies of between 0.1 and 100 Hz. Preferably, the tre~tment methods according to the '472 pa~ent involves the application of a~
least 2 and ~ore preferably at lea~t about 5 hig~ energy pul~e6 to the material being treated. The principal embodiment~ disclosed in the '472 patent involve the use of direct current. The techniques described in the '472 patent have several disadvantages. Most notably, electrolysis is caused with resultant electrode loss, cont~mination, and, at least in the case of eggs, detrimental coagulation. To mitigate this problem, the '47~ patent requires the use of me~branes interposed between the electrodes and the food product being treated. The '472 patent also fail~ to appreciate that highly functional egg having out~tanding storage stability can be obtained without the need for the complicated pulsed electrical treatment disclosed therein.
Most importantly, the '472 reference does not appreciate the difficulties attendant the continuous pasteurization of liquid egg. Specifically, nothing in the '472 patent discusses the proble~s attendant ensuring the absence of detrimental coagulation. Most notably, even though the '472 patent does describe arcing as a potential problem, the only effect attributed~to such arcing i6 damage to the electrodes.
Furthermore, all of the tests conducted in accordance with the '472 patent of liguid ~gg involve the use of static, bench testing d~vices at peak voltages of 34,000 volts or higher and currents ranging from between 7,200 and 14,200 amps. No continuous egg proce~si~g was undertaken. As will be described further her~in, when 2~8~33 similar static testing was underta~en by the present inventor~ u ing the technQlo~y describ~d herein, totally coagulated egg resulted.
To date, the '472 patent has, apparently, not been the subjet o~ commercial use nor are the present inventor(s) aware of any egg product being produced in accordance with its teaching. Thus, whether or not a sufficiently functional egg product can be produced with 6uch ~etho~ologies and apparatus i5 unknown.
In accordance with the present invention, there iE provided a ~ethod of pa teurizing li~uid egg which inclu~es providing liquid egg and electroheating the liquid egg using electric current having a frequency which is effective to heat the liquid egg without electrolysis. Electroheating of said liquid egg is conducted ~o as to avoid detrimental coagulation. $he electroheated liquid egg is held for a period of time which is su~ficient to achieve pasteurization. The electroheated liquid egg is then cooled. Thereafter, the electroheated pasteurized liquid egg can be packaged, or can be stored in a conventional manner.
The pasteurized electrsheated liquid egg just described, unexpectedly has a degree of microbial kill which is greater than t~at which could ~e expected from the use of a plate heat exchanger, under the same time and temperature conditions. In a preferred embodiment in accordance with the present invention, there is provided a method of pa6teurizing liquid egg which includes providing preheated liquid egg at a temperature of from about 125 F to about 144F and electroheating the liquid egg to a t~mperature of from about 150F to about 165'F. Thereafter the electroheated liquid egg is held for a period of between about 5 minutes and about O.S second~ re~p~ctively to acco~plish pasteurization~ The liquid egg is then cooled and packaged.
In ano~her preferred e~bodiment in accordance with the pre6ent invention, there is provided a method 208~93~

of pasteurizing liquid -gg which includes providing liquid egg and electroheating the liquid egg, using electric current having a frequency effective to heat said liquid egg without electrolysis. Electruheating is conducted at a rate of between greater th~n zero and less than about 36F/sec. ~nd is conducted s~ ~s to avoid detrimental coa~ulzlti~n~ Thereafter, the electroh~ated liquid egg is held for a period of time which is 6u~ficient to achieve pasteurization. Th~
electroheated liquid egg is then cooled. In a preferred embodiment, the electroheat~d liquid egg may also be packaged and preferably aseptically packaged.
It mi~ht be that li~uid egg can only be heated so fast, regardle~s of the other factors inv~lved. More likely however, the fact that liquid egg suffers from these problems when electroheating becomes more rapid is due to limitations of the electro~eating cell rather an inherent characteristic of liquid egg. Of course, it is preferable to heat liquid egg as guickly as a particular device will allow and begin cooling as soon as possible so as to minimize detrimental coagulation or other heat damage to the liquid egg.
The methods of the present invention have many advantages. Generally higher temperatures can be applied to the liquid egg to achieve pasteurization.
This will result in a greater degree of microbial kill increasiny not only the ~afety of the resultin~ liquid egg, but also the shelf life or storage stability thereof. These benefits are obtai~ed without detrimental coagulation or electrolysis. For example, despite the use of metal electrode6, and principally metal plate electrodes, the electrodes do not impart heat directly to the liquid egg. They are not, therefore, the heating surfaces, rather they are heated by the electroheated liguid egg. Caking and coagulation problems nor~ally as~ociated with the use of plate heat exchangers are eliminated by the use of electroheating in accor~ance with t~e methods o~ the present invention.

2~8.~93~

Furthermore, higher temperature pasteurization can be achieved without the disadvantages of oth~r high temperature heating ~echniques such as, for example, the use of ~team. Water introduced into the egg in the form of ~team will not have to be separated therefrom nor i5 it necessary to conduct any part of the process under high wacuum conditions. T~ere is neither a need to use c~mplicated and delicate membranes to prevent electrolysis nor a need to use very high energy, high current density electric pulses to achieve a highly effective level of microbi~l kill.
A number of advantages also inure from the use of electroheating in accordance with the ~resent invention to pastPurize liquid egg~ Electroheating provides a very uniform way of heating liquid eg~. Heat does not radiate forming a gradient inwardly from hot metallic plates. Instead, the egg i5 a resistor in the path of electricity traveling between the electrodes and a~ such, ~eat is generated internally and substantially homogeneously throughout the egg. The uniformity obtained by such treatments is extremely important in the production of a consistent product.
Furthermore, while not wishing to be bound by a particular theory of operation, it is believed that the passage of electric current throuqh the liquid egg provides a level of microbial kill above and beyond that which could normally be obtained through the use of other heating methods and devices using the same time and temperature conditions. It is believed that at least some of the microbes found in egg are, in effect, electrocuted in accordance with the process of the present invention. This provides for a more ef~ective method o killing bacteria and other microbes. Some of the microbes may be weakened by either the thermal treatment, the electrocution, or both. Then, apparently, instead of recovering fr~m their injured ætate, t~ese microbes eventually die, furthering the co~pleteness o~ the pa~teurization.

2~g~

Th~se theories find some ~upport in the '472 patent. That thes~ theories are applicable to electroheating in accordance with the present invention $ind~ ~ome support in the testing und rt~ken by the pre~ent i~ventor~. Li~lid whole egg tr~ated in accordance with the present invention showed a lower rate of re-~rowth of c~ertain bacteria over time follo~ing pa~teurization when compared ts liquid whole egg pasteurized under id~ntical conditions using a plate heat exchanger. This indicates a more complete microbial kill, greater safety, and greater storage stability, both at refrigerated temperatures and above 40F.
In addition, oertain tests indicate that liquid egg electroheated in accordance with the present invention continued to exhibit a decreasing level of microbes during refrigeration, day~ and even weeks after pasteurization. It is believed that this phenomena is a result of injured microbes dying~
In accordance with this aspect of the present invention, there is provided a ~ethod for imp~rting increased storage stability to li~uid egg. The method includes providing liquid egg; electroheating the liquid egg using electric current having a frequency effective to heat said liquid egg without electrolysis so as to avoid detrimental coagulation. This treat~ent will impart additional kill of spoilage inducing microbes contained in the liquid egg. Finally, the electroheated liquid egg is cooled.
In a preferred embodiment, the above method involves electroheating already pasteurized liquid egg and, in a~more preferred embodiment, the liquid egg is electroheated to a temperature which is greater than the temperature u6ed to pasteuriz~ the liquid egg.
Pasteuri~ation of liquid egg kills all of the bacteria posing an immediate health risk contained th~rein. Pasteurizing liquid egg can, in addition, impart a degree of kill o~ ~poilage ~icrobes or bacteria -8- 2 0 ~
s~ as to increa6e the shelf stability of the resulting product. ~y the u e of the method~ of the present invention, liquid egg inoll~ding already pasteurized liquid egg, is subsequently processed using electrohea~ing t~ further improve the level of kill of ~poilage miGrobes over and ab~ve the level of ~uch kill achieved during pasteurization.
Inter~stingly, becau~e o~ the better kill profile achi~ved using electroheating, it is po~ible to electroheat already pasteurized liquid egg to a temperature which is lower than that used to achieve pasteurization, and yet still achieve better storage stability. However, it is preferred that the pre-pasteurized e~g be further processed by electroheating at a temperature which is in excess of that used to pasteurize the liquid egg. This should provide an even l~rger d~gree of kill of ~poilage microorganisms.
In accordance with this aspect of the present invention, there is provided an apparatu~ for pasteurizing liquid eyg which includes an electroheating cell. The electroheating cell contains at least one pair of electrodes having egg engaging surfa~es spaced apart from one another to form a gap through which liquid egg to be pasteurized i6 passed. The ~5 electroheating cell has a source of high frequency electric current operably linked to the electrodes. A
holding chamber or holding tube in fluid communication with the gap for receiving liquid egg flowing through the gap is also provided as is a means for receiving and cooling electroheated liquid egg fl~wing from said ~olding c~amber.
In a preferred embodiment in accordance with the present invention, the electrodes used in the ~pparatus are generally parallel plate el~ctrodes having highly smooth, non-wetting ~urfaces with rounded edges.
In a highly preferred embodiment, the electrodes are disposed in an electroheating cell such that the edges 2~8~33 g of the electrodes do not directly contact liquid egg being proc~ssed through the cell.
While not wishing to be bound by any particular theory of operation, it i6 believed that the metal edges of plate electrodes could provide a source for fluctuations in current density. More imp~rtantly, it i~ po~sible that at these edges, current density increa~es and arcing ~ay occur. It is al~o po6sible, short Qf arcing, that the increased current density causes ~hot spots~ which are detrimental to the overall heating of the liquid egg. Rounding the otherwise sharp metal edges of the electrodes is believed to provide better and more uniform heating. Eliminating the edges entirely by tapering th~ ends or by encasing or embedding the edges of the electrodes in an insulating material is, however, preferred~
The preferred embodiments of the present invention will be described in greater detail with re~erence to the accompanying drawings, wherein like members bear like reference numerals and wherein:
FIG. 1 is a schematic representation of one configuration of an electroheating pa~teurization ~f the present invention.
FIG. 2 is a top plan view of an electroheating cell in accordance with the pre~ent invention.
FIG. 3 is a cross-sectional side view of the electroheating cell of FIG. 2 wherein the electrodes ha~e rounded edges~
FIG. 4 is a cross-sectional side view of an electrodP.
FIG. 5 is a plan view o~ a cooling device in accordance~with the present invention.
FIG. 6 is a cross-sectional side view of an electroheating cell in which the edges of said ~lectrodes are embedded or encased in in~ulating material.
The term liquid egg in accordance with the pre~ent invention i~ meant to include not only liguid 3 ~

egg white and liquid egg yolk, but combinations of each i~ any predQtermined or Idesirable ratio. The term liquid egg also includes liquid egg white, li~uid egg yolk, or combination~ thereof (referred to as ~liquid whole egg~) with additive~ such as salt~ sugar, milk, stabilizers, dextrins, cyclodextrins, peroxides, acids ~nd foodstu~fs including solid or particulate foodstuffs. Liquid egg from which cholesterol has been re~o~ed is also included.
~he term ~electroheatin~ in accordance with the present invention is meant to encompass a process of generatin~ heat in liquid egg by passing a current through the li~uid egg. The liquid egg acts as a resistor and hea~ is generated thereby. A particularly 1~ preferred technique for electroheating food is described in U.S. Patent No. 4,739,140 which has previously been insorporated by reference. In electroheating, the electrodes do not get hot as a result of the flow of current. In fact, in a preferred embodiment, affirmative steps are taken to ensure that the electrodes do not get hot. The only heat used to raise the temperature of the liquid egg is generated within the liguid egg itself.
As used herein, the terms ~pasteurizatio~, ZS ~pasteurize~, and npasteurized~ refer to the killiny of sufficient pathogenic microorganisms contained within liquid egg ~o as to render the liquid egg edible without thrsat of, for example, salmonell~ infectio~.
~Pasteurization~ may also be thought of as a treatment which is designed to eliminate, for all practical purposes, pathogenic microorganisms and, secondarily, to reduce the-nu~ber of spoilage microorganisms present to improve the keeping quality o~ the liquid egg product~.
At U.S.D.A. ~inimum ti~e and te~perature parameters, p~steurization will generally produce liquid whole egg which will have a refrigerated shelf life of between about 7 and about 14 daysO

6~ 9 3 3 ~Ll-~ Extended refrigerated shelf life~ means that the liquid egg i~ safe to consume for a period of at least 3 weeks after treatment in accordance with the present invention. This, of course, assumes proper re~rigerat d storage. Preferably, the term ~xtended refrigerated 6helf life~ means that the liquid egg is safe to consume for a period of at least 4 weeks after treatment in accordance wit:h the present inven~ion and more often 10 to 12 week~ after treatment, or longer.
~Greater storage stability~ means that the pas~eurized liquid e~g ha~ a longer shelf life, refrigerated or ot~erwise, when compared to liquid egg pasteurized under identical operating conditions in terms of time and temperature, by conventional, non-electrical methQds.
The methods and apparatus of the present invention will be better understood with reference to the schematîc diagram of FIG. 1. F~r the purposes of illustration only, the discussion with re~ard t~ FIG. 1 will involve the use of liquid w~ole egg. Of course, a device of the same configuration could be used in conjunction with the electroheating and pasteurization of other forms of liquid egg as previously de~cribed.
Liquid whole egg is transferred from holding tank 1, usually a refrigerated holding tank, to balance tank 2. 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. Any conventional means of heating can be utilized to preheat the liguid egg such as ovens, vats and/or steam infusions systems. In addition, electroheating ~ells can be used to preheat the liquid egg from refriger~ted or room temperature up to about 144F or higher~
A particularly preferred ~ethodj however, involve~ the u~e of a conventional plate heat exchanger 4. Liquid whole egg traveling from timing pu~p 3 is introdu~ed into plate ~eat exchanger 4 and ~pecific~lly into the regeneration section 5 thereof.

2 ~

~12--After passing thr~ugh the regeneration section 5, the temperature of the liquid w~lole egg is elevated to from, for example, 35~-40F to about llO~F~ Thereafter, th~
liquid whole egg is .introduced into heatinq section 6 of plate heat exchanger ~ where the temperature is further elevatPd from about 110F to between about 120F and about 14~F. In a preferr~d embodiment, preh~ating temperature~ of between about 135F and about 149F, and ~ore preferably, be~ween about 140-F and 144F are used f~r liquid whole egg.
Of c4urse, it is possible to use a single stage heat exchanger ~o accomplish the entire preheating ~tep or to use a heat exchanger having more than just two heating and~or regeneration sections to provide a more gradual heating thereto.
Thereafter, the liquid whole egg pass~s between the two electrodes of an el~ctroheating cell 7 and through the gap defined therebetween. In electroheating cell 7, high frequency electric current which is ef~ective to heat the liquid egg without electrolysis is ~pplied to the liquid egg in such a way so as to avoid detrimental coagulation. For example, liquid whole egg entering electroheating cell 7 from the aforementioned plate heat exchanger 4 would be elevated in temperature from about 140-F to about 151F.
Preferably, pasteurization temperatures of greater than about 150F will be attained for pasteurizing liquid whole egg and more preferably between ab~ut 150F and about ~65F. Most preferably, pasteurization temperatur~s of between about 150F and 160~F can b~
realized.
A~ter being electroheated as disclosed herein, the electroheated li~uid whole egg is then passed throu~h ~old.ing tubes 8 where it is held for a period of time ~ufficient to co~pl~te pasteurization in accordance with the Federal Regulation~. At a flow rate of about 228 pounds o~ liquid whole egg per minute and with a preheating temperature of 142-F and an electroheating ~99~

temperature of 150.8~F, the holding time can be, for example, about 3.54 minutes.
After the liquid whole egg has w~rked its way through holding tubes 8, it reaches flow diversion valve 9. If the temperature of the liquid egg exiting holding tubes 8 is below a pre~et value, then it is presumed that pasteurization has not been completed and th liquid egg is channeled back to balance tank 2 through ~low diversion valve 9. If, however, the temperature of a liquid egg i~ at or higher than the preset temperature, the liquid whole egg is allowed to proceed to a means for cooling slectroheated liquid egg 10. Thereafter, the cooled pasteurized liquid whole egg may be held in a tank, transported to a tank car, or directly packaged using a packaging device 11.
When cooled in cooling device 10, the pasteurized electroheated liquid egg preferably returns to a refrigerated temperature of between ~bout 35F
and 40-F.
With the foregoing as an overview, an apparatus useful in accordance with the methods of the present invention will be better understood. The use of a refrigerated holding tank 1 is conventional in the industry for holding both proces~ed and unproce6sed liquid egg products. It is of course not e~sential that a holding tank be utilized in accordance with the present invention. Specifically, liquid egg can be introduced into a pasteurizer from any source ~uch a~ a tank car, an egg breaking line or the like. Similarly, balance tank 2 and timing pu~p 3 are conventional in the pasteurization of liquid egg and, indeed, in use in connection~-with other liquid foods. Their substitution with known equivalents is acceptable as is their c~plete omission, dep~nding u~on the particular needs of the pa~teurization apparatus used.
Plate heat exchanger 4, as discu~ed previously, can include a preheati~g section or regeneration ~ection 5 and a he~ting ~ection 6. It i~

14 2 ~ 3 r O3 not, howeYer, limited therPto. The plate heat exchanger ~ may also i~clude, in additio~ thereto, sections whlch will cool and/or refrigerate liquid egg when passed therethrough. It is also possible that a 5 single eha~ber heater or heat exchanger be used wherein the temperature of the liqu:id egg is elevated from, for example, about 40~F to about 140~. ot~er devices as pre~iously discu~sed can al~o be used for preheating.
ElectrohQatin~ cell 7 include~ an i~let 71 and at least one pair of electrodes 72 spaced apart from one a~other defining a gap 74. It is through this gap 74 that the li.quid egg being pasteurized in accordance with the prese~t invention passes. The electrodes 72 are, in one embodiment, generally disposed such that their egg engagi~g surfaces 75 are substantially parallel to one another. It is particularly preferred that the egg engag.ing ~urfaces 75 of electrodes 72 are generally rectangular in shape, however, other shapes for both electrodes 72 and egg engaging surface6 75 are also acceptable. Regardle~s of shape, however, t.he cell 7 should be de~igned and the electro~s 72 placed in such a way that the sharp edges 79 of the electrodes 72, if any, do not come in contact wit~ the liquid egg being pasteurized, directly. There are many ways to effectively i.solate or eliminate the exposed sharp edges 79 of electrodes 72 so that they do not come i~to contact with the liquid egg being pasteurized~ One way, as illustrated in FIGS. 2~4 is to provide electrodes 72 having rounded edges 79. The edges 79 could al~ be eliminated by a gradual taper in the electrode surfac2.
It is preferred, however~ that the edges 79 of the electrode~ 72 be enca~ed in a ~uitable insulating material 73 as illustrated in FI~
The insulating material 73 ~ay al~o be used to assist in spacing opposing pair6 o~ electrod2s ~rDm ~ne another. The in~ulating material 73 may be, for example, made of plastics ~uch as Teflon or ceramios.
In a pref~rrQd embod.i~ent, however, edge~ 7~ of e,S
~15-electrode 72 are encased or em~edded in nnon-tracking plastic~" &uch as ~ELRIN, a polyacetate homopolymer available from DuPont or CELCON, an acetal copolymer available from Cellanese Corporation. ~Non-tracking polymers~ ~re poly~ers whic!h will prevent the fDrmation of current passages, channels, or tracks of low re istance therethrough. Ther~fore, these mat2rials can provide an effectiYe insula~ion in accordance with the present inY~ntion~
It is also impoxtant that t~e electrodes ~2 and most preferably, the ~gg engaging surfa es 75, b~
extremely smooth and rdifficult to wet or adhere to Similarly, it is greatly preferred that the flow of egg through electroheating cell ~ be unimpeded. Therefore, relatively straight electroheating cells are preferred.
A source of high frequency electric current (not shown) i5 operably connect~d to the electrodes 72.
The term ~high frequ~ncy" in accordance with the present invention is intended to include frequencies which are high enough to prevent the electrolysis of food products and the electrodes when in use andr more preferably, frequencies lying in a range of between approximately 100 Hz and 450 KHz. More preferably, high frequency in accordance with the present invention means the use of current6 having a frequency of between about 100 KHz and 450 KHz and more preferablyt between about 150 KHz and 450 KHz.
In general, electroheating in accordance with the present invention utilizes electric fields having a strength of 1000 volts/cm or lower and usually, in practice, less than 500 volts/cm. Similarly, relatively low current densities are used. In fact, current densities below 6 amps/cm2 are utilized more preferably current densities with less than 3 amps/c~2 are usedO
It is most pre~erred, h~wever, that current den6ities below about 1 amp~cm2 be used.
The power supply or source of high frequency electric current should be capable ~ providiny a ~8~3~

-:L6-constant flow of energy to the li~uid eggs through electrodes 72. In carrying out testing in accordance with the inv~ntion, a Westinghouse Pill~r Industries, lO0 ~Watts RF generator was used. The generator was capable of operation at lO~ to 45~ KHz and is rated at 200 KVA input fxom a ~0 Hæ line using ~Q volts. The RF IyPnera~or was operated at a frequency of about l~0 ~Hz and 38 KWatts.
~he presant invemtors have found that in the pasteuri~ation o~ liquid egg by el~ctroheating in accordance with the present inven~ion, it is i~portant that a uni.form current density be used. It is therefore preferable that steps be taken to eliminate the possibility of current density fluctuations. Steps which may or may not be necessary depending on the dictates of a part.icular system include: the use of a highly stabilized, hi~h frequency energy generators; th2 use of very smooth electrodes which discourage the adherence of liquid egg thereto during electroheating;
t~e occlusion of the metal edge~ of plate electrode6 such that the edges do not come in contact with the liquid egg being pasteurized; and limiting the rate of heating in a given electroheating cell.
Without wishing to be bound by a particular theory of operation, lt is believed that the edges of plate electrodes are a source of current den~ity non-uniformity. It is believed thzt much higher current densities are found at the sharp metal edges of plat~
electxodes and therefore considerably m~re heat :is generated in their region. For that reason, egg passing by an edge will be heated to a greater degree than egg pas~ing t~rough the remainder of khe el~ctrical field.
Such overheating can cause ~corching, o~agulation~
and/or begin a chain reaction which lead~ to the ~oullng of the pasteurizer~ There ar~ ~imilar phenomena which are thought to occur when ~gg begins to adhere to the egg engaging surfac2 75 of electrodes 72.

-:17-The si~e and spac:ing of the electrodes 72 and the power output of the source of high frequency electric current or power supply used in accordance with the present invention are also of concern.
Electrodes 72 must be of suf~icient size to allow for the convenient proce6sing of a sufficient quantity of liquid egg. They must al~30 be of sufficient size ~o allow for the heating of liquid egg at current densities which are sufficient to achiev~ the desired level of heating without detrimental coagulation. Detrimental coagulation includes caking on the electrodes, creation 0~ too YiscouS an egg product, the appearance of cong~aled clumps dispersed throughout the pro~ess of liquid ~gg, and~or the complete fouling of th~
pasteurizer.
Of course, the actual size of the electrodes 72 can vary widely depending on the ~requency of the power used, the amount of power which will be introduced acro~s the electrodes 72 in a given period of time, the speed with which the liquid egg i5 to be ~eated, and the differential in temperature which i5 to be obtained by electroheating. When very low current densities are used, the electrodes 72 may need to be rather l~ngthy to achieve large temperature increasesO
On the other hand, if heating is to be extremely rapid and relatively high current densities are used, relatively small electrodes 72 must be used.
A~ illustrated in ~IGS. 2, 3 and 6, it is also pos~ible to use a plurali~y of oppos~d pairs of electrodes 72, hooked in serie~, or in parallel instead of a single p~ir Qf electrodes. It i~ also possible that di~ferent pairs of electrodes can be operated at different frequenci~s. In this way it may be possible to impart an even yreater degree o~ ~icrobial kill9 In a particularly pre~erred embodiment, the electrodes 72 in accordance with the present invention are cooled t~ continuously dissipate heat rereived by being i~ contact with the electroheated li~uid egg.

2~8~

Cooling of the electrodes 72 can be accomplish~d in an~
manner, such a~ for example, passing tap water over the reverse side of or through the electrodes. The latt~r is illustrated in FIG. 4 where channels 78 are used to carry a cooling fluid through the ele¢trodes 72. ~he cooling fluid is recycled a~d i5 introduced i~o electrodes 72 through inlets and out again through outlet~ (not shown). Other cooling ~ethods include chilled water, glyc~l solutions, air and the like.
If particularly high temperatures are to be utilized in accordance with the practice of the present invention such as, for example, 180F, it may b~
necessary to more rapidly ~eat ~he liquid egg so as to avoid detrimental coagulation. In addition to rapid heating, under such circumstance~, it will be necessary that the holding time used to hold the liquid egg at an elevated temperature be lessened and that the onset of cooling be hastened. It is necessary in these cases to use greater current densities in order to rai~e the temperature of the liquid egg more rapidly. Electrodes would therefore be xelatively smaller allowing the pa~sage of more watts of power through a smaller space in the same amount of time.
The degree of preheating is dictated by the various economies of energy utilization. Generally, however, because the heat imparted to liquid egg in plate heat exchangers, for example, is recover~ble ~nd can be used in cooling liquid egg, it is often advisable to preheat t~e liquid gg to as high a temperature as feasible. For li~uid egg white, preheating temperatures be as high as about. 134F. Preheating temperat~res of about 125-~ may be used, if peroxide is added to the liquid egg whit2. The liquid egg yolk, preheating temperatures of about 142 are pre~erred. HoweY~r/
preheating te~peratures in excess thereo~ are also acceptable. The liquid whole egg, preheating temperature~ may range a~ high as about 149~F.
Preerably, however, preheating i~parts a temperature of ~:L9- ~
between about 140 and about 144F, or lower.
Conven~ional downstream proce~sing including approximately a 3.5 minut:e holding time have b~en as~med.
5Similarly, and a~;suming that the liquid egg being treated in electroheating cell 7 i5 to be proces~ed, and more importantly, held for an extended peri~d of time (between about l and about 5 minute~) than the maximum pas~eurization temperatures for liquid 10egg white, wit~ or without peroxide is about 131~F. The ~aximum pasteurazation ~emperature for liquid egg white can b~ elevated as high a~ a~out 150F if functionality, emul~ification properties, and the like are not important. Liquid egg yolk may be elevated to a 15temperature of about 157F and liquid whole egq may be heated to a temperature of between ~bout 153 and about l55F.
of course, and as discu~sed elsewhere herein~
electroheating in accordance with the present invention 20allows for a more rapid temperature change than possible through, for example, a plate heat exchanger.
Therefore, it is possible to reach much higher pasteurization temperatures than otherwise possibleO
When such temperatures are obtaine~, a raduced holding 25time and more rapid cooling may be needed to avoid detrimental coagulation. Nonetheless, through the practice of the present invention, it is possible to pasteurize liquid egg at temperatures well above 150F
and in fact up to at least about l8QDF, or higher.
30As suqgested above, in a preferred e~bodiment electroheat.ing is accomplished by elevating the temperature of the liquid egg in electroheating eell 7 at a rate of about 36FJsez. or less. Of course, ~ome rate of temperature change, i.e. grea~er than a zero 35change temperature is utilizedO It is particularly preferred however, that the temperature of the liquid egg be elevated as rapidly as pos~ible. Thus, -20 ~ J~
el.ectroheating is preferably conducted at a rat~ of between about 10F/sec. thrc~ugh about 18C F~ec.
Each individual electroheating cell may be structurally and energetically different. A particular el~ctroh~ating cell, for example, may under certain conditions, be capable of pasteurizing liquid whole egg at a rat~ of about lG n F per ~econd while the same operating conditions in a diferent electroheating cell will produce a te~perature change as rapid, for example, for 40~F per second. at that ratP of temperature chanye the latter electroheating cell may be plagued by arcing, detrimental coagulation, and/or caking. In the former electroheating cell, however, past~urized li~uid egy having the advantageous properties described herein will results withou~ incident. Of course, the former electroheatlng cell is i~capable, under these operati~g parameters, of operating as efficiently in terms of throughput as the latter electroheatin~ cellO
Furthermore, to obtain particularly high temperatures, it may be necessary, or even critical to limit the thermal exposure of the liquid egg to very brief periods of time, for example, less than abou~ 1 second. Under such circumstances, the former electroheating cell will not provide acceptable results.
It is not practicable tc provi.de optimal.
operatiny voltages, electrode sizes and degrees of separation and the like for every electroheating cell because of the variability of the de~ign of electr~heating cells. However, and witho~t con~ideration of the specifics of the el~ctroheating cell, if temperature changes are maintained approximately within the ranges prescribed herein, succ~ssful processing, partic~larly on large scale long-ter~ baæis should result.
Upon exiting electroheating cell 7 thrsugh outlet 80, the electroheated liquid egg passes through holding t~bes 8. The length o~ holding t~bes 8 and the flow rate of the liquid egg i~ determinatlv~ of the ~18~
-21~
amount of time at which the liquid egg remains in holding tubes 8~ Holding tube~ 8 maintain the liquid egg at or close to the temperature obtain~d during electroheating in electroheating cell 7. During conYentional pa~teurization at conYentional temperature~, holding times of ~etween 2~5 and 5 minutes are ~tandard practiceO
However~ as the t:e~perature of the liquid egg inereases, it ~ay be necessary to shorten the amount of holding t.Lme so as to avoid detrimental coagulation which may result from maintaining liquid ~gg at a specific el~vated temperature for too long. When egg i5 he~ted to a temperature of, for example, about 180F, detr.i~ental coagulation may ~egin in a matter of a fraction of a second. The holding t.in~e in such cases may be little more than the time necessary ts trallsfer the liquid egg from electroheating cell 7 to a cooling means lO. Holding time~ of as lit~le as one second, or less, may be efficacious~
When the temperatures used in accordAnce with the present invention are, ~or ~xample, below 16UF, however, it may be necessary for a more extensive holding period to be utilized. In such cases, it may b~
necessary to employ a flow diversion valve g which insures that liquid egg exiting the holding tubPs l~as been maintained at a suitable temperature for a p~riod of time long enough to insure pasteurizatlon. Of cour~e, pasteurization is confirmed separately by microbislogic and ot~er ~uality control methodologies.
If liquid egg flowing from holding tubes 8 is below a preset temperature, flow diversion valve 9 operates to divert the liquid egg back to balance tank 2 where it reenters the pasteurizer to be repa~teurizedO
If the temperature is at or above the pre~et temp~rature, however/ flow diver~ion valve 9 aliow~ for th~ liquid egg to continue in the pasteurization proce~.

~8~3~

~ fter heating, the liquid egg must be cGoled.
Certainly liquicl egg canno~: be maintained at elevated t~mperatures of above 140~ indefinitely. The higher the temperature used, the lDDr;e quickly cool ing neads to 5 begirl . If temperature~ below about 160 ~ F and more preferably below 155~F are utilized, it may be possible to employ a conventiorlal plate heat exc:hanger as the means for rec:eiving and coo:Ling the electrc~heated li~id ~qg 10. In fact, these coolislg se;::tlons may be the cooling sections of plate heat exchanger 4 previously discl?ssed. Liquid egg passing therethrough will pass through one or more sections where ~t will be cooled from its pasteurizatiDn temperature to an intermediate temperature. Then, the li~uid egg will be transferred to a refrigeration section of the heat exchanger and cooled to a refrigeration temperature of between about 35F and about 40~F. Any other form of cooling may be used so long as it provides ~uf~iciently rapid cooling to insure that no detrimental coagulation occurs.
When higher temperatures are used, it is important that cooling begin rapidly and be accomplished rapidly such that the liquid egg does not remain at elevated temperatures (over 140'F) for a time sufficient for a significant level detrimental coagulation to develop. When, for example, temperatures in a range of 170F to ~.80~F are used, it may be necessary to begin cooling and achieve a significant degree of cooling in fractions of a second. The sooner cooling is accomplished, the less detrimental coa~ulation will result. To accomplish this, a particularly preferred means for receiving and cooling the electroheated liquid egg 10 has been developed which essentially mixe~ the hot electroheated pa~teurized liquid egg and already pa~teuri~ed cold li~uid egg in a sufflci~nt ratio to insure rapid cooling ther~o~.
This particularly preferred apparatus for cooling the liguid egg is illu trated in FIG. 5 and 9 ~ 3 include~ a generally ~Y~-shaped device 30 having a fîrst conduit 3l for conveying a ~tream of hot electrohe~ted liquid egg and a second conduit 33 for conveying a ~tream of cold, paskeurized liquid egg. These two streams ~f liquid egg are brought together in a mixing cha~ber 35 such that they are intimately and quickly intermixed. The rapidity and degree of cooling obtained u#ing ~uch a device i~ a function of the ratio of hot a~d cold egg introduced into the ~ixing chamber, the ~0 respective temperatures of the streams, and the rate of combination. ~ot electroheated liquid egg i6 introduced into first conduit 31 throuyh a first inlet 32 and cold pasteurized liquid egg is introduced i.nto second conduit 33 through second inlet 34. Cooled liquid egg exits cooling device 30 and mixing chamber 3~ through outlet 36.
In a particularly preferred embodiment, initial cooling is accompli~hed by the use of device 30 just described. Additional cooling may, however, be obtained by the use of a secondary cooling means for ~urther cooling the liquid egg. ~his may be a conventional plate heat exchanger as previously described. After cooling by device 30, a plate heat exchanger, a combination of both, or some other device, a certain fraction of the now cooled egg intermixed with the cold egg can be recirculated back to the second conduit 33 to provide for the rapid cooling of additional hot electroheated liquid egg.
Liquid egg resulting from the practice of the present invention has several distinct advantag2s over liquid egg which i5 conventionally pasteurized. For reasons which are not completely known, liquid egg prepared in accordance with the present in~ention has a higher degree of microbial kill then could otherwise be expected without the u~e of elaborat~ electrocution apparat~s ~uch as disclosed in the '472 patent. ~s des~ribed further herein, comparative testiny has demonstrated that less re~growth of bacteria cccurs in 2~831~ ~c~;

~;2~-liquid egy in accordance with the present invention, even when the liquid egg is mainta~ned at room temperatuxe. In fact, the leYel of bacterial concentrat.ion in refrigerated liquid egg pasteurized by electroheating actually slightly decreased over a period of day after processing. Thus it is possible, by the practice of the present inYention, to provide liguid egg product6 of greater ~helf stabili~y and dramatically extended refrigerated 6helf life.
It is also apparent ~ha~ because of the ~ore effective kill obtained by electro~eating in acsordance with the present invention, less care needs to be exhibited in the storage of the liquid Pgg. This is particularly important because refrigeration of the liquid egg in, for example, supermarkets, is not always consistent. Packages containing pasteurized liquid egg are sometimes at the back of a refrigerated shelf where the temperature may be in the range of 35F to 40F. ~y the same token, li~uid egg may be placed at the front of the shelf exposed to the open air where the temperature may be as high as 50F. The problems of inconsistent refrigeration are further compounded by normal store practice of rotating stocks so that the oldest stock is at the front of the display to promote its rapid sale.
Not surprisingly, the degree of microbial kill and the degree of the liquid egg's resistance to x-e-growth of microorganisms is somewhat dependent upon the temperature and time parameters under which pasteurization .is undertaken. It should be readlly apparent, ~owever, that temperat~re in accordance with the present inventi~n directly translates to ~he amount of power i~put through the liquid egg in a given period o ti~e. The higher the level of heat, the greater the amount of electric current passing through the liquid Pgg. It can there~ore be expected that with higher temperaturQ~ and higher power level exposures, greater degree~ of pasteurization can be realized.

2 ~ 8 ~ 9 ~ et -:25-The eggs prepared in accGrdance with the present invent.iorl are also more likely to retain a greater degree of ~mctionality when compared to other li~lid egg. Electroheating as disclosed herein provides a greater degree of microbial kill than otherwise attainable through the use of conventional non electxically based technolot~. It ie therefore possible to pa~teurize using an electr4heating device at lower tempera~ure~ while still attaining the same or better level of kill as would otherwi e be expected from t.he u~e of; for example, plate heat exchangers. Because the liguid egg is more ~gently~ paskeurized, lesc denaturation and coagulation should result with lexs attendant loss of functionality.
Another advantage of electroheating for the pasteurization of liquid eg~ is that pasteurization can be undertaken ~ven w~en the egg is intermixed with other food stuf~s. As for example, raw liquid whole Qgg CGUld be mixed with such ingredients as chopped ham, onion, pepper, and the like and then pasteurized by electroheating. It is therefore possi~le, through the practice of the present invention to prepare, in raw form, all of the necessary ingredients for a western omelet. Then the ingredients and the liquid egg are electroheated such that the liquid egg is pastellrized.
This can be followed by packaging to produce an extended refrigerated self life liquid omelet mix.
The foregoing will be better understood with reference to the following examples. These examples are for the purposes of i].lustration. They are not to be considered limiting as to the scope and nature of the present in~ention.

~ Pl A cell having electrode~ of about 10~ by 3.5~
were constr~cted with a ~eparation of about la. Liquid whole e~g with citric acid (~12-ol7~ Wa6 filled intQ
the gap between the electrodes to a h~ t of a~out 3~

2~n9~

An AC current having a freeluency of 10 KHz, 600 volts, and 330 amps was appli~d to the li~uid egg. This yielded a field strength o2 about 336 volts/cm2 and a current density of about 1.'7 amps/cm2.
This energy was initially applied for 0.2 seconds. Thereafter, the egg temp~rature w~s measured and th~ quality of the ~gg evaluated. After 4 such 0.2 second applications, coagulation began. After the fifth application, a ~olid mass of cooked egg resulted. This initial test showed that electrical energy in accordance with the prPsent invention could be effective for electroheating li~uid egg. However, when this techni~ue was initially applied to a continuous liquid Pgg pasteurization proce~s, the results were not as promising. Arcing, caking, undesirable coagulation and odor resulted.
Exa~Dl ~
Liquid whole egg was electroheated in a continuous pasteurizer as illustrated in FIG. 1.
However, electroheating was conducted using an electroheating cell which was disposed after the holding tubes. The electroheating cell used a pair of plate electrodes 7~ x 1.5~ with a 0.5~ separation. The electrodes had small ~ecuring teeth around their periphery which were embedded into the insulation.
First, saline was run through the system at 110 amps, and 152 volts with a field strength of about 178 volts/cm2 and a current density of about 1.57 amps/cm2. A 10 XHz power source was used. A
c~ange in temperature of 33F from 147F to 180F was reali~ed. However, some arcing was observed at the higher rate of temperature rhange. A~ter a half an hour, liguid egg was processed through the sam~
apparatu~. The current used wa~ 7~ amps, the voltage wa~ 492 volts, the frequency was 9.4 XHz and 34 KWatts w~re usedO The temperature change achieved wa~
about 17~F from about 145F to 162F. However, arcing, ~oagulation and odor began a~ter about 3 minutes.

2~$~~
~27-This illustr~tes the problems r~alized when electroheating in accordance with the present invention was taken from the statiG, bench test to ~ c~ntinuous in-line eg9 processing apparatus.
~a~
In an atte~pt to mitigate the pr~blems realized in Example ~, a 170 KHz power supply was used with the cell de~cribed in æxample 2. When runni~g saline, no problems were o~erved. However t i~mediate arcing, coagulation and o~or resulted when the processing line was switched to liquid whole egg. It is believed that this test indicates that arcing and coagulation are problems associated with not only the design of the electrodes, but the inherent properties of liquid egg.
E~lo 4 Liquid whole egg with citric acid to protect color during ~rying was treated in an apparatus configured as illust~ated in FIG. 1. Cooling means lo were the variou~ cooling sections of a conventional plate heat exchanger. Liquid egg entering regeneration ~ection 5 of plate heat exchanger 4 entered at a temperature of about 40-F and left at a temperature of about 110~F. The liquid egg was then transferred to heati.ng section 6 of plate ~eat exchanger 5 where its temperature wa~ elevated to approximately 142F.
Thereafter, the liquid egg was transported to an electroheating cell 7 as illustrated in FIG. 2 where 31 kw per hour were applie~ to the liquid egg.
The flow rate through the electrodes was about 228 lbs~
per minute. The electroheating cell employed four sets of electro*es, each of which had a length of 18.5 cm, a width of 3.4 cm and a separation o~ 3~4 cm. The total surface area of the electrodes was approximately 250 c~2. While in electroheating cell 7, the liquid egg w~s subjected to high frequency current at approxi~ately 170 KHz, 210 amps, ~55 volts and a field strength of about 64 volts/c~.

2 ~ 3 ~

After electroheating, the liquid egg had attained ~ temperature of 66~C (150.8F). The liquid egg was then transported to holding tubes B and wa5 held for apprvximately 3.54 minutes. The temperature of the lig~id egg at th end of holding tubes 8 was about 150,8 D F. The liquid egg was then cooled using a conventional plate heat exchang~r and as~ptically pac~aged in gable top packages in a cher~y-~urrell model ~Q-3 aseptic packager.
Samples o the material prPpared in accordance herewith were h~ld at 3~-F and tested for total plate count over a period of 14 days. The results were reported in Table 1.
Table 1 Sample No.
~ _ 2 3 4 Treatment + 2 days 50 60100 --+ 6 days 60 6070 60 + 14 days 40 ~ 21 days 100 The results showed that the overall total plate count for liquid eqg electroheated in accordance with the present invention was excellent in terms of microbial kill and lower than is generally realized from similar treatments using, for example, plate heat exchangers. The total plate count decreased, albeit slightly, over a 14 day period following treatment.
Other samples of material were held at 70'F
for three days. The pH remained at 6.8, the color re~ained t~pical of eggs stored at 3~F, the viscosity remain~d typical of eggs stored at 38 n F and the odor remained typical of eggs ~tored at 38F. A control held under the same conditions exhibit~d a typical odor of ~ggs stored at 3~-F. ~owever, the viscosity o~ the liguid egg hang~d ts a pudding-like ViQCosity, the pH
dropped to between about 5.3 and about 5.6, and the ~8~
~9 co~or became bright yellow. This indicates spoilage and a gen~rally higher lev~l of active bacteria present in the liquid egg.
Finally~ liquid ~g~ processed in accordance 5 with this example was ried at 3 no ~ F on an open griddle.
The egg r~tained a typical flavor and texture. On average, the tot~l plate count for liquid whole egg treated by, for example, a plate heat exchanger at 150F
would be in the range of b~tween about 100 and ab~ut 500. H~w~v~r, low~r plate counts have been ob~er~ed from time to time.
R~lo s ~ iquid whole egg wit~ citric acid was processed as described in Example 4. However, the temperature of preheating through plate heat exchanger 4 was elevated from 142~F to about 148F. The liquid egg attained a temperature of 69-C (156.2F) during electroheating in electroheating cell 7. After being held for 3.54 minutes, the temperature of the liquid egg wa~ 155.3~F.
Liquid egg prepared in accordance with this example is held at 38F for a period of time and samples of this material were tested for total plate count. The results are report~d ~elow in Table 2.
Table ~

Sample No.
Pate 1 2_3 _. 4 Treatment date + 2 days 100 50 100 --+ 6 days 60 70 B0 70 - + 14 days 40 ~ 21 days 200 Again, the result~ obtained in accordance with thi~ test are re~lective of ~uperior level~ of ~cterial kill. In addition, it wa~ ag~in observed that ~he total plate count dimini~hed so~ewhat as long as 14 days after pa~teurization was effectuated.

~ ~o ~ 9 ~ ~ 3 Samples of liquid egg prepared in accordance with this example were held at 70 ~ for three days. T~e pH remained at 6.8, the color rem~ined typical of aggs stored at 38~F, the viscosi.ty remained typical of eggs 5stored at 38F and the odor remained typical of eggs tored at 3~F. The result~ of the contrQl were identical to those described with reference to Exa~ple ~. These observations, tak~n in accordance with the total pla~e count indicate the superior nature and 10the efficacy of electroheating as a technique for pa~teuriziny and for imparting extended storage stability to liquid egg.
Egg prepared in accordance with this example wa6 fried on an open griddle at 300F. The egg retained 15typical flavor and texture.
Ple 6 Liquid whole egg was processed as de~cribed above in Examples ~ and 5. The temperature of the liquid egg flowing out of plate heat exchanger 4 20was 142F and the temperature attained in e.lectroheat.ing was approximately between 6g-C and 70C for a brief period of time. Because of instability in the coils of the power supply used, and the rapid rate at which power levels were increased, arcin~ occurred at 70 C and 25detrimental coagulation began necessitating the shutdown of the system.
~mpl~ 7 Liquid whole egg without additives was electroheated to a temperature of about 15~F and held 30at that temperature for approximately 3.6 minutes.
Treatment was as d~scribed in Examples 4 and 5. Four samples were taken two days after pasteurization and initial tot~l plate counts were run. Sample 1 showed a tot~l plate count of 20, sample 2 showed a total plate 35count of 30, sample 3 showed a total pl2te count of 20, and sample 4 showed a total plate count of 20. This is extre~aly low by comparison to pasteurization by, for exa~ple, plate hea~ exchanger~ under th2 e conditions.

~3~ 3~, After 14 days~ the kotal plate s~unt for a single sample taken was ~Q.
~hole egg pasteuriæed in accordance with this example was maintained at '70'F for thre2 daysO The pH
of the electroheated liquid whole egg remained at 7.3 and the odor, color, and VlSCD~ity remained typical of eggs propexly stored at 38"F. In contra~t, the control showe~ a pH of between 5.3 and 5.7~ the color was bright yellow and the viscosity was elevated ~o that of pudding. The odor rem~ined acceptable.

Liquid whole eg~ with citric acid was pa~teuri~ed using the device illustrated in FIG. 1 and in accordance with the procedures qenerally described in Examples 4 and 5. Temperatures in electroheating cell 7 re~ched 150F. About 35,000 lbs. of liquid egg were processed and aseptically packaged i~ a cherry-burrell model EQ-3 aseptic packager. The initial total plate count of liquid whole egg taken two day6 after treatment wa6 18.
PI~ 9 Liquid egg as de~cribed in Example 8 was processed at a temperature of about 151~F. 55,000 lbs.
of liquid egg were processed. The initial total plate count resulting was 28.
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 parti~ular embodi~ents disclosed, since these are to be regarded illustrati~e rather than re~trictive. Variations and changes may be made by others without departing from the spirit and scope of the invention.

Claims

1. A method of continuously pasteurizing liquid egg comprising the steps of providing liquid egg;
electroheating said liquid egg with AC electric current having a frequency effective to heat said liquid egg without electrolysis, to thereby avoid detrimental coagulation; holding said electroheated liquid egg for a period of time which is sufficient to achieve pasteurization; and cooling said electroheated liquid egg.

2. A method of continuously pasteurizing liquid egg comprising the steps of providing liquid egg;
electroheating said liquid egg with AC electric current having a frequency effective to heat said liquid egg without electrolysis, at a rate of between greater than zero and less than 36°F/sec. to thereby avoid detrimental coagulation; holding said electroheated liquid egg for a period of time which is sufficient to achieve pasteurization; and cooling said electroheated egg.

3. The method of claim 2 wherein said electroheating is conducted at a rate of between about 10°F/sec. and about 18°F/sec.

4. The method of claims 1, 2 or 3 wherein said frequency ranges between about 100 Hz and about 450 KHz.

5. The method of claims 1, 2, or 3 wherein said electroheating is conducted using electrodes without edges exposed to said liquid egg.

6. The method of claims 1, 2 or 3 wherein said frequency is from between about 100 Hz to about 450 KHz and wherein said electroheating is conducted using electrodes without edges exposed to said liquid egg.

7. The method of claims 1 or 2 further comprising the step of preheating said liquid egg prior to the step of electroheating.

8. The method of claim 7 wherein said preheated liquid egg ranges in temperature from between about 120°F to about 149°F.

9. The method of claim 8 wherein said preheated liquid egg ranges in temperature from between about 135°F to about 149°F.

10. The method of claim 9 wherein said preheated liquid egg ranges in temperature from between about 140°F to about 144°F.

11. The method of claims 1 or 2 wherein said electroheating step is conducted so as to heat said liquid egg to a temperature greater than about 150°F.

12. The method of claim 11 wherein said electroheating step is conducted so as to heat said liquid egg to a temperature of from between about 150°F
to about 180°F.

13. The method of claim 12 wherein said electroheating step is conducted so as to heat said liquid egg to a temperature of from between about 150°F
to about 165°F.

14. The method of claim 13 wherein said electroheating step is conducted so as to heat said liquid egg to a temperature of from between about 150°F
to 160°F.

15. The method of claim 1 or 2 wherein said cooling is at least partially achieved by combining hot electroheated liquid egg with cold pasteurized egg.

16. A method of continuously pasteurizing liquid egg comprising the steps of providing preheated liquid egg having a temperature less than about 144°F;
electroheating said liquid egg with AC electric current having a frequency of between about 100 Hz and about 450 KHz to a temperature of at least about 150°F; holding said electroheated liquid egg for a period of between about 5 minutes and about 0.5 seconds respectively to accomplish pasteurization; and cooling said electroheated liquid egg.

17. The method of claim 16 frther comprising the step of packaging said electroheated liquid egg;

18. The method of claim 17 wherein said packaging is aseptic packaging.

19. The method of claim 16 wherein electroheating is conducted using electrodes without exposed edges.

20. The method of claims 16, 17, 18 or 19 wherein said cooling is at least partially achieved by combining hot electroheated liquid egg with cold pasteurized liquid egg in a predetermined ratio.

21. Apparatus for continuously pasteurizing liquid egg comprising an electroheating cell including a pair of electrodes having egg engaging surfaces spaced apart from one another to define a gap through which liquid egg to be pasteurized is passed, and a source of high frequency AC electric current having a frequency effective to heat said liquid egg without electrolysis operably linked to said electrodes; a holding chamber in fluid communication with said gap for receiving liquid egg flowing through said gap; and means for receiving and cooling said electroheated liquid egg from said holding chamber.

22. The apparatus of claim 21 wherein said egg engaging surfaces of said electrodes are generally rectangular.

23. The apparatus of claim 22 wherein said egg engaging surfaces of said electrodes are smooth.

24. The apparatus of claims 21, 22 or 23 wherein said cell is constructed such that said electrodes do not include edges exposed to said liquid egg.

25. The apparatus of claim 21 wherein said electrodes are disposed such that their egg engaging surfaces are substantially parallel to one another.

26. The apparatus of claim 21 wherein said means for cooling is a plate heat exchanger.

27. The apparatus of claim 21 wherein said means for cooling includes a first conduit for conveying hot electroheated liquid egg, a second conduit for conveying cold, pasteurized liquid egg; and a mixing chamber for receiving said hot electroheated liquid egg from said first conduit and for receiving said cold pasteurized liquid egg from said second conduit to intermix said hot electroheated liquid egg with said cold pasteurized liquid egg secondary cooling means to thereby cool said hot electroheated liquid egg.

28. The apparatus of claim 27 further comprising a secondary cooling means for further cooling said liquid egg in fluid communication with said mixing chamber and disposed to receive liquid egg therefrom.

29. The apparatus of claim 28 wherein said secondary cooling means for further cooling said liquid egg is a plate heat exchanger.

30. The apparatus of claims 26 or 27 further comprising a means for recycling at least a portion of said liquid egg from said mixing chamber to use as said cold pasteurized liquid egg.

31. A pasteurized liquid egg product produced in accordance with the method of claim 1.

32. A pasteurized liquid egg product produced in accordance with the method of claim 2.

33. A pasteurized liquid egg product produced in accordance with the method of claim 11.

34. A pasteurized liquid egg product produced in accordance with the method of claim 14.

35. The apparatus of claim 21 wherein said electroheating cell includes a single pair of electrodes.

36. Apparatus for rapidly cooling hot pasteurized liquid egg comprising a first conduit for conveying a stream of hot pasteurized liquid egg from a pasteurizer to a mixing chamber; a mixing chamber for receiving hot pasteurized liquid egg from said pasteurizer and for mixing said hot pasteurized liquid egg with a stream of cold pasteurized liquid egg; and a second conduit for conveying a stream of cold pasteurized liquid egg to said mixing chamber where it is received and mixed with said hot pasteurized liquid egg.

37. The apparatus of claim 36 further comprising a means of secondary cooling said mixed hot pasteurized liquid egg and said cold pasteurized liquid egg disposed to receive said mixture from said mixing chamber.

38. The apparatus of claim 37 wherein said means of secondary cooling is a plate heat exchanger.

39. The apparatus of claims 36 or 37 further comprising a means for recycling at least a portion of said mixed hot pasteurized liquid egg and said cold pasteurized liquid egg to said second conduit.

40. A method of rapidly cooling hot pasteurized liquid egg comprising the steps of intermixing hot pasteurized liquid egg with cold pasteurized liquid egg in a ratio sufficient to lower the temperature of said hot pasteurized liquid egg.

41. The method of claim 40 wherein the proportion of cold pasteurized liquid egg and the temperature thereof is selected so as to reduce the temperature of the hot pasteurized liquid egg to below pasteurization temperature.

42. The method of claims 40 or 41 further comprising the step of introducing said intermixed hot pasteurized liquid egg and cold pasteurized liquid egg into a means for secondary cooling and secondarily cooling said mixture to a temperature below 65°F.

43. A method for continuously imparting increased storage stability to the liquid egg comprising the steps of: providing liquid egg; electroheating said liquid egg with AC electric current having a frequency effective to heat said liquid egg without electrolysis, to thereby avoid detrimental coagulation and so as to impart additional kill of spoilage inducing microbes thereto; and cooling said electroheated liquid egg.

44. The method of imparting increased storage stability to the liquid egg of claim 43 wherein said provided liquid egg is pasteurized liquid egg.

45. The method of imparting increased storage stability to liquid egg of claim 44 wherein the temperature of said liquid egg is elevated to a temperature above the temperature used to pasteurized said liquid egg.

46. The method of claims 43 or 45 wherein said frequency ranges between about 100 Hz and about 450 KHz.

47. The method of claim 43 or 45 wherein said electroheating is conducted using electrodes without edges exposed to said liquid egg.

48. A method of pasteurizing liquid egg comprising the steps of providing liquid egg;
electroheating said liquid egg with electric current having a frequency effective to heat said liquid egg without electrolysis, to thereby avoid detrimental coagulation; holding said electroheated liquid egg for a period of time which is sufficient to achieve pasteurization; and cooling said electroheated liquid egg.

49. The method of claim 6 wherein said frequency is between about 100 KHz and about 450 KHz.

50. The method of claim 4 wherein said frequency is between about 100 KHz and about 450 KHz.