Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 7
PRI:)I)UCIN~ ~15hl~15~ Rl~F~ hTB1~ B~ IFE:
li'OOD WITHOU~ Gll ~ lURB ~ ATING
This application is a Continuation-In-Part
application of Serial No. 07/862,198, filed
April 2, 1992. The present invention relates to a
method of providing food, and particularly liquid egg
with an extended refrigerated shelf life.
In recent ye~rs, a number of techniques have
been proposed for extending the re~rigerated shelf life
of food products which might contain pathogenic
bacteria, spoilage bacteria, or both . Swartzel et al O,
U.S. Patent No. ~,808,425, for example, suggests that
extended refrigerated shelf life on the order of four
weeks or more can be imparted ~o ~oods such as, for
example, liquid whole egg. According to
Swartzel et al. / this can be accomplished by combining
so-called ~ultrapasteurization~ conducted on continuous
flow, high temperature, short time pasteurization
equipment with aseptic packaging. Although it is
somewhat dif~icult to determine exactly what holding
temperature and time constitute ~ultrapasteurizationn,
from the discussion contained in Sw~rtzel et al., it is
clear from a review of the examples provided in Table II
thereof that heating was conducted on conventional high
temperature, short time commercial plate~type heat
exchange thermal processing systems at temperatures in
excess of 146~F and up to approximately 162~F and
holding times ranging from about 2.7 seconds to
about 3.2 minutes.
Dunn et al ., U . S . Patent No. 4,838,154 and its
parent, U.S. Patent No. 4,695,472 take a different
approach. Dunn et al. discuss methods and apparatus for
extending the shelf life of fluid food products
including eggs by the repeated application of high
voltage, high current density, discrete electric pulses
to food products. Field strengths used are, at
minimum, 5,000 volts/cm and voltages as high as, ~or
example, 37,128 volts are disclosed. Direct current
'''~ 2~2g7
2--
densities of ~t least about 12 amps/cm2 are also
disclosed as are pulse frequencies of between about 0.1
and 100. Preferably, the treatment involves the
application of at least two and, more preferably, at
least five discrete high energy pulses to the food being
treated.
Dunn et al. suggest that different forms of
energy, e.g. the application of different types of
pulses, can result in different ef~ects on the treated
food. For example, Dunn et al . disclose the use o~
flat-top electric field pulses wh~re heating is to be
kept to a minimum, and exponentially decaying pulses
where heating by electric field is beneficial.
Dunn 2t al. recognize the problems associated
with electrolysis of the electrodes and he food being
treated during the application of the pulsed energy high
energy fields. Dunn et al. therefore propose a device
including plate electrodes separated from the food being
treated by a membrane and having an electrolyte placed
therebetween in an attempt to mitigate this problem.
Dunn et al. teach that an exten~ed
refrigerated shelf life may be obtained in egg
containing preservatives by the use of 30 pulses of
electric energy having a peak voltage o~ 36,000 volts or
more, a peak current of at least 9,600 amps and a final
temperature of 136.4~F. Dunn et al. suggest, based on
this test, that fluid egg product containing additives
which is elevated in temperature to approximately 60~C
and stored at temperatures of about 4~C can provide
liquid egg with an extended refrigerated shelf life
of 28 days or more.
The additives used in accordance with
Dunn et al. are potassium sorbate and citric acid which
are termed chemical preservatives. The effects of such
additives on the refrigerated shelf life of liquid egg
is demonstrated in Fig. 13 of Dunn et ~1. where a
control which was treated using pulsed electric fields
but which did not contain additives ~1302-control) is
~ 0 ~
~3~
c ~red to liquid egg containing additives which had
been similarly treated and stored (1306-treated). A
significant shelf life extension appears to be directly
attri~utable to the presence of these additives.
Accordingly, the present invention provides a
method of pasteurizing liquid whole egg so as to impart
extended refriqerated shelf life thereto including the
~teps of: providing liquid whole egg; electroheating
the liquid whole egg to a temperature of between
about 140~F and about 145~F using AC electric current
having a ~requency effective to heat the liquid whole
egg without electrolysis and to avoid detrimental
coagulation; holding the electroheated liquid whole egg
for a period o~ at least about 2.5 minutes; cooling the
electroheated liquid whole egg; packaging the
electroheated liquid whole egg; and storing the packaged
electroheated liquid whole egg to a temperature of
between about 32~F and about 40~F. In particularly
preferred embodiments, the frequency of the AC electric
current used ranges from between about 100 kHz to
about 450 kH~ and more particularly from between
about 150 kHz to about 450 kHz.
It has been discoYered that by combining
electroheating techniques such as those disclosed in
U.S. Patent No. 4,739,140 and in Serial No. 07/862,198
filed on April 2, 1992 in the name of David R~znik and
Aloysius Knipper, the text of both being hereby
incorporated by reference, when combined with proper
packaging and proper storage, extended refrigerated
shelf life liquid egg results. Moreover, these shelf
lives can be achieved with or without the addition of
preservative additives.
Liquid egg processed in accordance with the
present invention has a maximum level of egg
functionality as it has not been subjected to heating
times and temperatures which can cause significant
coagulation and/or denaturation. Furthermore, liquid
egg produced in accordance with the present invention
20912~ ~
.~,
and properly stored as described herein is unexpectedly
found to possess an extended refrigerated shelf life of
at least six weeks and, more particularly, as many as 8
and 12 weeks or more, without the need for preservative
additives or the use of extensive high voltage-high
current electric pulse equipment. Most surprising,
however, is the discovery that for extended refrigera~ed
shelf lives of greater than six weeks, liquid whole egg
need not be both ~ultrapasteurizedn as described by
Swartzel et al. and aseptically packaged as described by
Swartzel et al. In fact, extended refrigerated shelf
lives of eight weeks or more can be achieved without
using either aseptic packaging or ~ultrapasteurization~.
The preferred embodiments of the present
invention will be described in greater detail with
reference 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 pasteurizer of the
present invention.
Fig. 2 is a side elevational view, in section,
of a concentric electrode electroheating element
constructed in accordance with the concepts of the
invsntion.
Fig. 3 is a somewhat schematic flow chart of a
multi-step electroheating device utilizing concentric
electrode of Fig. 2.
Fig. 4 is a simplified schematic drawing of
the device of Fig. 3.
The term ~liquid egg~ in accordance with the
present invention is meant to include not only liquid
egg white and liquid egg yolk, but combinations of each
in any predetermined or desirable ratio (referred to as
~liquid whole egg~). The term liquid egg also includes
liquid egg white, liquid egg yolk, or liquid whole egg
with additives such a~ salt, sugar, milk, stabilizers,
dextrins, cyclodextrins, enzymes, antibiotics,
peroxides, acids such as citric acid and foodstufPs
_5_ 2 ~ ~2 g~
including ~olid or particul~e foodstu~f~. Liquid eyg
from which cholesterol has been removed is also
included. While it is possible in accordance with the
present invention to add stabilizers and acids, or, in
fact, add peroxide during processing, the addition
thereof is not necessary in accordance with the present
invention to provid~ ext~n~e~ re~rigerated shelf life of
six week~ or greater~
As used herein, the terms ~pasteurization~,
~pasteurize~, and npasteurized~ refer to the killing of
sufficient pathogenic microorg~n; ~ contained within
liquid egg so as to render the liquid egg edible without
threat of, for example, salmonella infection ~or a
period of time. ~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 number of spoila~e
microorganisms present to improve the keeping quality of
the liquid egg product. The times and temperatures used
which are sufficient to at least meet U.S. Department of
Agriculture requirements for the pasteuri~ation of
liquid egg are as follows: Albumen (without use of
chemicals) 134~F and a holding time (average particle
time) of 3 1/2 minutes; whole egg 140~F, 3.5 minute
holding time; and whole egg blends (less than 2% added
non-egg ingredients), 142~F and a 3.5 minute hold.
The term nextended refrigerated shelf life~ in
accordance with the present invention means that the
liquid eqg and, in particular, the liquid whole egg, is
safe to consume for a period of at least about 6 weeks
and, more preferably, greater than between about 8 and
about 12 weeks or more. Extended refrigerated shelf
life in accordance with the present invention requires,
however, substantially continuous storage of-the liquid
egg at refrigerated temperature~ of 40~F or below just
following pasteurization.
The term ~electroheating~ in accordance with
the present invention is meant to encompass a process of
2~9~
--6
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 electroheatiny food is described
in U.S. Patent No. 4,739,140 and another is described in
United States Patent Application Serial No. 07/862,198
filed April 2, 1992 previously incorporated by re~erence
herein.
~Electrolysis~ is an electrochemical process
which can be characterized by at least two specific
phenomena. One form of electrolysis results in the
dissolution o~ the me~al electrodes inserted into the
food being treated. As ions flow between a pair of
electrodes, the metal at the surface of the electrodes
becomes ionized by releasing electrons to positive ions
in the food. The metal ions then 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 molecules such as the
conversion of hydrogen ion to hydrogen atoms and then to
hydrogen gas molecules. Similar processes take place
with regard to chlorine, hydroxide ions and the like.
These conversions can adversely impact the flavor and
other advantageous qualities of the treated food both as
the result of direct depletion of the ions and their
conversion to other species and by initiating other
reactions within the food such as oxidation and
reduction.
~Detrimental coagulation~ in accordance with
the present invention refers to the coagulation of
proteins within the liquid egg such that there are
visible particles of egg and/or the loss of
functionality. Through the practice of the present
invention, liquid egg having viscosity, color, and
pourability of shell egg and its components are
maintained.
The methods and apparatus of the present
invention will be better understood with reference to
~12~
-7-
the schematic diagram of Fig. 1. Of course, devices of
other configurations known to be useful in conjunction
with the pasteurization of food and, in particular, the
pasteurization of liquid egg can also be used. Liquid
whole egg is transferred from holding tank 1, usually a
refrigerated holding tank, to balance tank 2. Of
course, liquid whole egg can be taken from a tank truck
or tank car or directly ~rom an egg breaking line as
well. Thereafter, the liquid whole egg is pumped
through a timing pump 3 which keep~ the liquid whole egg
moving throughout the entire pasteurization apparatus.
~he liquid whole egg is then preferably preheated. Any
conventional means of heating can be utilized to preheat
the liquid egg such as ovens, vats and/or steam infusion
systems. In addition, electroheating cells can be used
to preheat the liquid egg from refrigerated or ambient
temperature up to about 144~F. Of course, if
pasteurization will be conducted using temperatures
of 140~F, the maximum preheating temperature utilized
must be below 140~F.
A particularly pre~erred method of preheating,
however, involves the use of a conventional plate heat
exchanger 4. Liquid whole egg traveling from timing
pump 3 is introduced into plate heat e~ch~nger 4 and
specifically into the regeneration or preheating
section 5 thereof. After passiny through the
regeneration section 5, the temperaturè of the liquid
whole egg is elevated ~rom its initial temperature to a
temperature of up to about 120~F. Therea~ter, the
liquid whole egg is intxoduced into heating section 6 of
plate heat exchanqer 4 where the temperature is further
elevated to between about 120~F and about 144~F and,
more preferably, between about 130~F and about 139~F.
Of course, it is possible to use a single stage heat
exchanger to accomplish the entire preheating step or to
use a heat exchanger having more than just two heating
and/or regeneration sections to provide a more gradual
heating thereto.
2~9~
Thereafter, the liquid whole egg passes
between at least two electrodes o~ an electroheating
cell 7 and through the gap defined therebetween. In
electroheating cell 7, high freguency electric current
which is effective to heat the liquid egg without
electrolysis is applied 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 ~ch~nger 4 would be elevated
in temperature to ~rom about l~O~F to about 145~F and,
~ore preferably, between a temperature greater than
about 140~F to about 1~5~F. The specifics o~
electroheating cell 7 are fully set ~orth in the
aforementioned U.S. Patent Application Serial
No. 07J862,198 filed April 2, 1992 which was previously
incorporated by reference herein. Generally, however,
liquid egg is transported between a pair o~ electrodes
and high frequency alternating current is passed
therethrough as previously described. In general,
electroheating in accordance with the present invention
uses a source of high frequency electric current which
is operably and electrically connected to the
electrodes. The term nhigh frequencyn in accordance
with the present invention is intended to include
~requencies which are high enough to prevent the
electrolysis of food products and the dissolution of the
electrodes when in use and, more preferably, frequencies
lying in the range of between approximately 100 Hz
and 450 kHz. More preferably, high frequency in
accordance with the present invention means the use of
currents having a frequency of between about 100 kHz and
about 450 kHz and, more preferably, between about 150
kHz and about 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. Similaxly, relatively
low current densities are used. In fact, current
2~ 2~
g
densities of below about 5 amps/cm2 are utilized. More
preferably, current densities of less than
about 3 amps/cm2 are used and mvst preferably, the
current densities used are about 1 amp/cm2 or less.
The power supply or source of high ~requency
electric current used should be capable of providing a
constant flow of energy to the liquid egg through the
electrodes. In carrying out testing in ~ccordance with
the invention, a Westinghouse Pillar Industries
Model 125K67, 100 KWatts RF generator was used. The
generator was capable of operating at 100 ~z to 450 kHz
and is rated at 200 KVA input for a 60 Hz line using 480
volts. The RF generator was operated at a frequency of
about 170 KHz to about 220 KHz and about 38 KWatts to
achieve a 5~F temperature change at a ~low rate of
about 25,000 lbs. per hour. All repeated voltages are
~peak to peak~.
An alternate electroheater is also useful for
carrying out the processes of the present invention.
As is shown in Fig. 2 electroheating cell 7
is made up of a body 20 which i~ stainless steel.
Body 20 is the first electrode of the concentxic
electrode pair included in electroheating cell 7~. In a
particularly preferred configuration, body 20 has a
first cylindrical portion 22 and a second cylindrical
portion 24 of a lesser outer diameter connectad to the
first cylindrical portion 22 by a tapered section 26.
At the free end 28 of cylindrical portion 24 is an inlet
tube 30 through which liquid egg may be introduced in
the direction of arrow 31 into the gap between the
electrodes as will be more fully described below.
Adjacent the opposite free end 32 of the cylindrical
portion 22 is an outlet tube 34 through which the
electroheated food may exit in the direction of ~rrow 37
to holding tubes 8 or to further eleotroheating
cells 7~. As illustrated in Fig. 3, outlet tube 34 of
the leftmost electroheating cell 7~a is connected to t~e
- ' 2 ~
--10--
electroheating cell 7~b at inlet tube 30 thereof by
means of suitable tubes or piping 36.
A cylindrical cooling jacket 38 can be placed
about cylindrical portion 24 of body 20. An inlet
tube 40 is provided to the cooling jacket 3~ at the
upper end of cylindrical portion 24 adjacent tapered
portion 26 and an outlet tube 42 is provided adjacent
the free end 28 of cylindrical portion 24. Fluids such
as cold liquids (water, glycol or alcoholJ or cool~d
1~ gases may be circulated through cooling jacket 38 to
help conduct away heat generated by the electroheating
carried out within the cell 7~.
A jacket 66 of insulation or other protective
of these materials may be placed outside of body 20 and
cooling jacket 38 to prevent heat or cooling loss and/or
to protect nearby operators.
Also placed in free end 32 of cylindrical
portion 22 is an aperture 44 into which is fitted an
insulator 46 which may be made of non-tracking materials
of rubber, ceramics or plastic. In a preferred
embodiment, the insulator 46 is made of DELRIN, a
polyacetate homopolymer available from DuPont or CELCON,
an acetyl copolymer available from Celanese Corporation.
Insulator 46 contains a central aperture 47
into which is placed the second or central electrode 50.
A series of O-rings such as ~9 and 51 are disposed in
central aperture 47 which engage the outer surface of
central electrode 50 when it is placed in aperture 47 of
insulator 46 to prevent the passage of the liquid egg
out of cell 77 along the outside of central electrode 50
or the passage of external cont~ i n~nts into the cell 7~
by the same route. Fitted above insulator 46 about the
free end 32 of cylindrical portion 22 is a hollow
cap 53. Two threaded studs 55 are anchored in
insulator 46 at one end and exit via corresponding
apertures in cap 53. The threaded studs 55 pass through
corresponding apertures in a support plate 57.
Adjustment nuts 59 are placed on the threaded ~tude 55
20912~ ~
on adjacent both surfaces o~ support plate 57. The
entire central electrode 50 can be moved upwardly within
hollow cap 53 by tightening up on adju~tment nuts 59
above khe support plate 57, while the ones below
plate 57 limit the extent of upward movement. By
loosening the nuts 59 above plate 57 the entire central
electrode 50 can be lowered into body 20 limited by the
inclined shape of the insulator 46 its~lf.
The central electrode 50 is fabricated o~
~tainless steel. Central elec~rode 50 may be made up o~
a central tube 52 with a rounded distal end 54 giving
the general appearance of a test tube. ~ source of RF
energy is connected to tube 52 via the support plate 57
which is electrically connected to each of the central
electrodes 50 of each of the cells 7~ of the
electroheater so that the central electrodes 50 can act
a~ the second electrode of the electroheating device.
The source of high frequency AC electric current used
was an ~F generator which provided a constant current by
varying the voltage.
A tube 60 is inserted into tube 52 so that its
distal end is short of the distal end 54 of tube 52. A
source of cooling fluid as previously described is
connected to inlet 62 of tube 60 and allowed to flow out
into tube 52 and are removed at outlet 64 at the
opposite end of tube 52 from distal end 54.
Turning next to Fig. 3, there is shown a
multi-cell electroheater including a plurality of sight
glass electrode cells and the concentric electrode
cells 7n just described. Sight glass electrode cell 100
is added at the product input line 99 to the first
electroheating cell 7~a of the electroheater. The sight
glass electrode cell 100 includes metallic end plates or
conductive collars 102 and 104 separated by an
insulative glass tube 106 o~ appropriate length,
diameter and bore. The end plate~ 102 and 104 act as
electrodes and current passes between them against and
parallel to the flow of ~ood as explained belowO Glass
.t 2 ~ '~
-12-
tube 106 may be composed o~ an insulating glass material
such as KIMAX brand heat resistant glass available from
Kim~le Glass. The end plates 102 and 104 include an
aperture through which food can pass. In fact, the end
plates 102 and 104 are generally just conductive pipe
used to carry the liquid egg to and from the tube 106.
A collar and seal are used to seat and attach the
insulating tube 106.
Food enters the electroheater through conduit
or input line 99 and it flows into electroheating
cell 100. The food flows through the aperture in first
electrode or end plate 102 into ~he interior of the
hollow insulating member, glass ~ube 106. Finally, the
food exits sight glass electrode cell 100 by passing
through the aperture in end plate 104. End plate 104 is
connected to one side 74 of a resistor or tank coil 72.
The other side 76 of resistor or tank 72 is connected to
the second terminal 73 of high frequency RF power
source 70, which is the system ground. End plate 104 is
also connected to the output of the concentric
electrodes, common return g2, as described herein. End
plate 102 is connected to system gro~nd teL ; nat 73 o~
power source 70 through lead 113~o Glass tube 106 has
an inside diameter of about 2~ and length of about 14~.
A second sight glass electrode cell 110 is
provided and is constructed in the same manner as sight
glass electrode cell 100. This second sight glass
electrode cell 110 is in fluid c' ication with
outlet 34 of the concentric electrodes to receive food
electroheated in cell 7ne. Electroheating cell 110 has
an end plate 112 . connected to the system ground
terminal 73 of source 70 via lead 113. End plate 114 is
connected to the side 74 of resistor or tank coil 72 and
to said common return 92. A second glass tube 116 is
disposed between the respective end plates 112 and 114.
Each of said end plates or electrodes 112 and 114 have
an aperture through which food enters the electroheating
cell 110 and exits therefrom, thus exitiny the
2 ~
-13-
electroheater. Glas.s tube 116 has an inside diameter
of 2n and a length o~ 16~. The remaining elec~roheating
cells used are the concentric electrode containing
cells 7~.
In operation, food is electroheated in
electrsheating cell 100 by the passage of high ~requency
AC current from end plate 104 to end plate 102. The
food then travels through inlet tube 30 into concentric
electroheating cell 7~a and between electrodes 20 and 50
thereof. As illustrated in Fig. 3, once the food is
electroheated again between electrodes 50 and 20 of
electroheating cell 7~a, the liquid food flows through
outlet tube 34 thereof which is connected to a second
concentric electrode containing electroheating cell 7~b
by means of a suitable tube or pipe 36. Concentric
electrode containing electroheating cells 7~c, 7~d
and 7~e are connected to each other and to
~lectroheating cell 7~b in the same manner that
electroheating cell 7nb is connected to electroheating
cell 7~a. ~fter being electroheated in concentric
electrode containing cell 7~e, the food exits through
outlet 34 and then enters into sight glass electrode
cell 110 where it is again electroheated. The food ~hen
leaves the electroheater through the aperture in
electrode 112.
The flow of electric current through the
system takes a quite different path. First, high
frequency AC electric current leaves RF generator 70
through output 71 and is fed by lead 90 to the five
concentric electrode containing parallel electroheating
cells 7n. (For illustration purposes, 3200 volts.) The
high potential lead 90 is actually introduced directly
into electroheating cell 7nb through electrode 50
thereo~. Other leads take the energy to each of the
other electrodes 50 o~ electroheatin~ aells 7n,
respectively.
The average voltage drop acro~ the gap
between all electrode~ 50 and electrode~ 20 is, for
209~
-14-
example, 200 volts. Thus the voltage read at
electrodes 20 should be approximately 3000 volts.
The 200 volts drop is transferred to the food as heat.
The current applied at about 38 KWatts power and 200
volt drop is about 190 amps. Of course, currents of up
to about 400 amps or more are also contemplated. As
shown in Fig. 4, the electrical energy remaining after
electroheating food in electroheating cells 7~ is then
transferred to other portions of the electrohe~ter by
common return 92. In Fig. 4, common return 92 i~ shown
as a lead. In fact, high ~requency RF energy can travel
along the outer skin of the concentric electrode
containing cells 7n and from one cell to another via the
pipes or conduits (inlet 99, inlets 30, outlet 34,
connecting tube 36, and the like). Common return 92
conveys electric current to each of the sight glass
electrodes 100 and 110 through end plates 104 and 114,
respectively. Common return 92 is also connected to
resistor or tank coil 72 at end 74 thereof which is
arranged in series with the sight glass electrodes 100
and 110. Three thousand volts is therefore applied
across tank coil 72 and across the sight glass
electrodes 100 and 110.
To complete the current flow, the electric
energy traverses the gap between end plate 104 and end
plate 102 and end plate 114 and end plate 112,
respectively, each o~ which is linked back to system
ground 73 via leads 113' and 113, respectively. A
second end 76 of resistor or tank coil 72 is also
attached to system ground 73. The resistor or tank
coil 72, in one embodiment, is a coil of copper tubing.
In another embodiment, however, the tank coil or
resistor 72 s merely a 20~ or 30' long piece of copper
tubing (1/2~ to 5/8~ outside diameter). Although the
copper tubing has a very low resistance, much lower than
the resistance of, for example, liquid whole egg in the
sight glass electrodes 100 and 110, it has an inductance
which provides a sufficient voltage drop. There~ore, a
9~7
--15--
substantial portion o~ the curren~ of the system r~turns
to system ground 73 through resistor or tank coil 72,
thereby bypassing the sight glass electrodes lOo
and llO. This explains why the sight glass electrodes
described herein are relatively high voltage (3000 volts
peak to peak) and relatively low current
(approximately 15 amps calculated). Higher or lower
currents are also contemplated. Such a device is
disclo~ed in a U~S. patent application filed on
iO January 22, 1993 in the name of Thaddeus Polny bearing
Attorney Docket No. Papetti 3.0-017 entitled ~ethods
and Apparatus for Electroheating Food Employing
Concentric Electrodes. n
After being electroheated as described herein,
the electroheated liquid whole egg is then passed
through holding tube 8 where it is held ~or a period of
time sufficient to complete pasteurization in accordance
with Federal Regulations. At conventional processing
rates and temperatures ranginy from between about 140~F
to about 145~F, liquid whole egg should be held for at
least about ~.5 minutes and, more preferably, between
about 3 and about 4 minutes. Most preferably, liquid
whole egg is held for a period of time oP about 3.5
minutes.
After the liquid whole egg has worked 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 preset value, then it is
presumed that pasteurization has not been complete ~nd
the liquid egg is channeled back to balance tank ~
through flow diversion valve 9. If, however, the
temperature of the liquid egg is at or higher than the
preset temperature, the liquid whole egg is allowed to
proceed to a means for cooling electroheated liquid
egg 10~
When cooled in cooling device 10, the
pasteurized electroheated liquid egg preferably returns
to its refrigerated temperature of between about 32~F
2 ~ ~ ~ 2 ~ ~
-16-
and about 40~F. Cooling device lO may be any device
use~ul for cooling electroheated pasteurized liquid egg
~uch as those described in the aforementioned U.S.
Patent Application Serial No. 07/862,1~8 ~iled April 2,
5 1992. However, preferably, cooling device 10 is the
cooling and refrigeration sections 14 and 16
respectively of plate heat e~ch~nger 4. In Fig. l, this
is illustrated as 10'. In this con~iguration, liquid
whole egg which has been pasteurized and held at the
10 preset temperature for the required holding time exits
flow diver~ion valve 9 and enters the
cooling/regeneration section 4 of plate heat exchanger 4
through conduit 12. There, the liquid whole egg is
cooled from its pasteurization temperature to a
15 temperature of between about 120~F and about 60~F.
After leaving cooling/regeneration section 14 of plate
heat exchanger 4, the cooled liquid whole egg enters
refrigeration section 16 of plate heat exchanger 4
wherein it is rooled to a refrigerated temperature of
greater than about 32~F and lower than about 40~F.
Thereafter, the refrigerated liquid egg can be
sent to a holding vessel for short term, long term or
intermediate term storage, sent to a tank car or truck
or, more preferably, sent directly to packaging
device 11. Of course, as was the case with heating, it
is possible to cool the liquid egg using a single
section heat exchanger or a heat exchanger having more
than two cooling ~ections. It is also possible to use a
totally discrete plate heat exchanger. Cooling can al50
be accomplished by any other conventional method such
as, for example, the use of refrigerators, the use of
chilled gases, and the like.
Packaging device 11 need not be aseptic. The
present inventors have realized that by the practice of
the present invention including electroheating and
storage at 40~F or under, it i8 not nec~ssary to
aseptically package processed pasteuri~ed liquid egg in
order to obtain an extended refrigerated shelf life and,
2 0 9 ~ 2 ~ ~
-17-
more particularly, an extended refrigerated shelf life
of eight weeks or more. Aseptic packaging procedures
are described in 21 C.F.R. 113.3, 113.40(g)
and 113.100(a)(4). Generally during aseptic proces~ing,
a commercially sterilized product is in~roduced 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, li~uid 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 1,300,000 packages. Aseptic packaging can be
accomplished with, ~or example, using an International
Paper Model SA aseptic packager or a Scholle Model 10-2~
aseptic packager. Of course, aseptic packaging may be
utilized in accordance with the present invention.
However, by processing in accordance with the present
invention, it need not be.
Another type of packaging use~ul in accordance
with the present invention is the so-called nclean packn
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 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 a~ discussed below.
For example, if the packages are not treated with a
peroxide spray prior to ~illing, they can be considered
sanitized, but not aseptic or ~clean packs~.
2~2~7
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Also use~ul in accordance with the present
invention are plain sanitized clean container~ pxoduced
and sanitized using ~good manufacturing procedures~ 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 ePfect of proper refrigerated storage, ~uch
an addition o~ cells is not considered signi~icant.
These aforementioned packages which are all
specifically useful in practicing the present invention
to provide extended shelf li*e may be contrasted with a
~dirty package~ which has not been sanitized nor
1~ 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 cell~ re~aining in pasteurized liquid egg
after successful pasteurization.
Again for illustration purposes,
pasteurization at normal tempexatures of between
about 140~F and about 145~F through a conventional plate
heat exchanger will result in liquid egg having
approximately lO0 cells per gram. The use of higher
temperatures such as 150~F or more may result in, for
example, a 10 cells per gram. Electroheating in
accordance with the present invention between
about 140~F and about ~45~F may provide a product
containing one cell per gram. Based on one liter
packages, the total cells per a liter package
are 100,000, lO,OOO and 1,000 respectively.
If electroheated li~uid whole egg processed in
accordance with thP present invention is added to 100
one liter plain containers properly sanitized, using
sanitary filling procedure~, 99 o~ th~ resulting
packages should contain 1,000 total cells with the one
r~maining package containing 1,001 total cells. As will
be readily apparent, even using packages which have
2 0 ~ r3J
--19--
merely been sanitized, the number of cells introduced in
packaging is relatively in~ignificant when compared to
the number of cells introduced in~o th~ package in the
liquid egg. It is only when ~dirty packages~ are used
that a signi~icant increase in cells is realized.
Other types of packages and packaging
devices 11 may also be used. It is preferred that these
packaging devices be capable of providing an exten~e~
shelf life package. These packaging devices and
te~hn~ques include vacuum packaging, controlled
atmosphere packaging, and modified atmosphere packaging
can all be used.
The present inventors have found that by
electroheating in accordance with the present invention
utilizing high frequency alternating electric current
and by maintaining the electroheated liquid egg at a
refrigerated storage temperature of approximately 40~F
or below, tremendous ~dvantages can be realized. The
resulting liquid e~g has most, if not all, of its
original functionality and little, if no, detrimental
coagulation. In addition, the liquid egg has an
unusually low content of residual ~acteria and,
particularly, spoilage bacteria so that with proper
refrigerated storage, extended refrigerated shelf life
of eight weeks or more can be achieved. All of this is
accomplished without the need for the use of high
energy, high current e~uipment and without the need for
stabilizers as suggested by Dunn et al. ~urthermore,
the resulting refrigerated shelf lives are 100% greater
30 than those disclosed by Dunn et alSimilarly, the
result of the present invention can be achieved without
the need for ~ultrapasteurization~ as described by
Swartzel et al. and without the need for aseptic
packaging.
The foregoing will be better understood with
reference to the following examples. These examples are
for the purposes of illustration. They are not to be
209~g ~
-20-
considered limiting as to the scope and nature of the
present invention.
E~
Table Ready brand liquid whole egg was
pasteurized at 142~F utilizing an ele~troheating
pasteurization device as illustrated in Fig. l and
described herein. A Cherry-Burrell model EQ3 packager
was used as packaging device 11, without use of a
peroxide spray. The resulting packages can therefore be
classified as sanitized packages, but not aseptic
packages or nclean packn packages as defined herein.
Two pound sanitized gable top containers were used for
packaging. Two pounds of citric acid per 1,500 lbs. of
liquid whole egg was added to reduce the pH to between
about 6.6 and about 6.9. This amount of citric acid is
sufficient to prevent reactions with iron in the egg
yolk which might otherwise turn the yolk green, but
insufficient to provide any appreciable stabilization or
preservative effect on the shelf life of the liquid egg.
No other preservatives or stabilizers were used. After
pasteurization and packaging, the liquid egg was stored
at a temperature of between about 33~F and about 34~F.
Tests were immediately undertaken to determine the
presence of salmonella, listeria, total plate count,
Coliform, and staphylococcus. All testing utilized
standard microbiological methods known in the industry.
Initially, the liquid whole egg was negative for
salmonella, st2phylococcus and listeria, had an initial
average total plate count of 95, and had less than lQ
colonies of Coliform. After eight weeks, total plate
count was 20, the Coliform was unchanged.
~x~m~l~ 2
Table Ready brand liquid whole egg was
pasteurized as described in Exampla 1. Initial tests
for salmonella and staphylococcus were negative, the
initial average total plate count was 22.5, less than lO
colonies of Coliform were present. Listeri~ Was t~sted
at four weeks on Nove~ber 30, l9g2 and the tests
2 ~
-21-
conducted were negative. After eight weeks, the total
plate count was 20, and the Caliform numbers were
n~h~nged-
~ 3
Table Ready brand liguid whole egg was
pasteurized as described in Example 1. Initial tests
for salmonella, listeria and staphylococcus were
negative and Coliform showed less than 10 counts. The
initial average total plate count was 32.~. After eight
weeks, the total plate count was 20, and the Coliform
count was unchanged.
~x~mpl~ 4
Table Ready brand liquid whole egg was
pasteurized as described in Example 1. Initial tests
for salmonella and staphylococcus were negative, the
initial Coliform count was less than ten. The initial
average total plate count was 17. 5. Listeria was tested
a~ter ~our weeks on December 2, 1992 and the tests were
negative. After eight weeks, the total plate count
was 80 and the Coliform count was unchanged.
~$~1Dlpl6~ 5
Table Ready brand liquid whole egg was
pasteurized as described in Example 1. Initial testing
for salmonella, listeria and staphylococcus was
negative, Coliform was less than 10 counts, and the
initial average total plate count was 15. After eight
weeks, the total plate count was 10, and the Coliform
numbers were unchanged.
The liquid whole egg resulting from the five
forsgoing examples was unspoiled, organoleptically
superior and safe for general consumption and use even
after eight weeks.
The principles, preferred embodiments, and
modes of operation of the present invention have been
described in the foregoing specifi~ation. 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 as
- 2 ~
-2~-
illustrative rather than restrictive. Variations and
changes may be made by others wi~hout departing from the
spirit and scope of the invention.
