Patent Application
20160324170
The invention pertains to pasteurizing chicken shell eggs using the radio frequency electromagnetic wave energy.
The FDA standard for pasteurizing chicken shell eggs is a thermal treatment that is validated for achieving a 5 log kill of Salmonella Enteritidis throughout the entire egg including the yolk and the albumen. A D-value (measured in minutes) is the amount of time that it takes to statistically achieve a ten-fold reduction (i.e. a log reduction), of a pathogen (e.g., Salmonella Enteritidis) in a substance held at a certain temperature. D-values for Salmonella Enteritidis are known to be higher in egg yolk than in albumen, which means that it is more difficult to kill Salmonella Enteritidis in the egg yolk than in albumen. Shell egg pasteurization system using heated water baths are based in part on the notion that heating a shell egg in the water bath requires heat to transfer through the shell and through the albumen to the yolk, so the temperature of the albumen will necessarily be greater than the temperature of the yolk when the egg is coming up to the temperature of the water bath. According to current FDA requirements, the yolk temperature and the albumen temperature must be at least 128° F. before Salmonella Enteritidis is killed reliably.
The Davidson '538 patent (U.S. Pat. No. 6,165,538) provides a statistically derived line plotting the 5 D-value (i.e., five times the D-value) for shell eggs inoculated with Salmonella Enteritidis having yolk temperatures from 128° F. to 138.5° F. As the egg yolk heats from 128° F. to the water bath temperature, the log reduction accumulates and continues to accumulate as the yolk is maintained at or near the water bath temperature. In fact, log reduction continues to accumulate even after the shell egg is removed from the pasteurization bath until the yolk temperature drops below 128° F.
Present day commercial scale shell egg pasteurization facilities use large heated water baths to gently warm stacks of eggs sufficiently to achieve the required 5 log kill of Salmonella Enteritidis. These large heated water bath systems are sometimes not practical. For example, maintaining large heated water baths at the precise temperature needed for accurate pasteurization is not practical in low volume or variable volume applications. Large water baths may not be desirable in certain geographical areas with water restrictions as well. Further, pasteurization in water baths requires that the shell eggs be coated, e.g. wax, in order to replace the protective cuticle on naturally-laid shell eggs that is removed when the eggs are pasteurized in a water bath. In fact, many countries in Europe do not allow shell eggs to be washed or pasteurized in water baths because they do not want the cuticle removed.
One of the difficulties with pasteurizing shell eggs in a heated water bath is that the heat, as mentioned, is conducted through the shell and through the albumen before it is available to heat the yolk. Thus, the albumen typically receives a harsher thermal treatment than the yolk even though Salmonella Enteritidis is much easier to kill in the albumen than the yolk of the shell egg. D-values for Salmonella Enteritidis for yolk in a shell egg at 134° F. is about 7 minutes, whereas the D-value for albumen at 134° F. is about 0.7 minutes. The D-value of Salmonella Enteritidis in albumen at 132° F. is 1.25 minutes, which is still less than the D-value for the yolk at 134° F. International Egg Pasteurization Manual, Froning et al., July 2002, page 9. In other words, approved methods for egg white pasteurization require about 3.5 minutes at 134° F. and 6.2 minutes at 132° F. (to achieve at least a 5 log kill), and kill values are higher if albumen pH increases with storage time before pasteurization.
If the albumen is overheated it will begin to denature and cross link, which in turn results in cloudiness and increased whipping time for the egg white to reach full whip peak. Further overheating will lead to coagulation. Therefore, when pasteurizing in heated water baths, great care is taken to ensure that the yolks of the eggs are heated sufficiently to achieve the required 5 log kill of Salmonella Enteritidis while at the same time not overheating the eggs which can lead to lower quality albumen.
Others in the art have attempted to pasteurize chicken shell eggs using radio frequency electromagnetic wave energy with limited success. One of the more difficult problems in using radio frequency electromagnetic wave energy in the past has been the difficulty of achieving uniform heating and not overcooking and causing coagulation in the albumen. Dev et al. published a paper in 2012 entitled “Optimization of Radio Frequency of In-Shell Eggs Through Finite Element Modeling and Experimental Trials”, Progress in Electromagnetics Research B, Volume 45, 203-222, 2012 that discussed the testing and modeling of the heating of an artificial chicken egg with radio frequency electromagnetic waves for the purpose of pasteurization. The artificial egg was modelled to be a glass egg filled with egg white or albumen. The modeling was verified using a computer-controlled parallel plate radio frequency wave applicator (27.12 MHz) using an actual artificial glass egg filled with egg white. Dev et al., page 212, found that heating in a parallel plate RF applicator was highly non-uniform if the eggs were kept static between the plates, which would lead to the generation of hot spots and cold spots throughout the egg. Dev et al. found on page 2013 that the closer the static egg is to the electrodes, the faster the egg white is heated as compared to the egg yolk which would likely lead to increased coagulation of the egg white proteins. Dev et al. also found on page 2014 that rotating the artificial eggs between the electrodes led to more uniform heating and preferentially faster heating of the area in which the yolk is located than the albumen, as is preferred for pasteurization of actual shell eggs. Dev et al. does not model shell eggs with distinct yolk and albumen components or make any findings regarding the requirements for achieving a 5 log kill of Salmonella Enteritidis in the yolk or in the albumen.
U.S. Pat. No. 8,973,492, entitled “Method and Apparatus for Pasteurizing Shell Eggs Using Radio Frequency Heating” issuing on Mar. 10, 2015 to Geveke et al. applies 60 MHz radio frequency energy by placing electrodes in contact with opposite sides of a rotating shell egg. One or both of the electrodes comprises a brush or mesh. Geveke et al. also run cooling water over the shell to cool the albumen from overheating and preferentially heat the yolk. Geveke et al. explains that the penetration depth of radio frequency energy increases as frequency decreases, so RF energy having a frequency in the range of 10 MHz-100 MHz should heat the yolk better than microwave energy.
It is believed that contacting the shells with electrodes at commercial scale pasteurization facilities may lead to production difficulties. It is also believed that contacting the shells with electrodes may compromise the integrity of the shells, and lead to breakage or premature contamination issues. Therefore, one of the objects of the present invention is to pasteurize shell eggs without contacting the shell with the electrodes.
Another object is to provide a system that does not require the use of water. Shell egg water bath pasteurization technology is more than adequate for large scale operations where water usage is not an issue. Where water conservation is a priority, a waterless shell egg pasteurization system may be more practical and commercially favorable.
The invention is directed to methods for pasteurizing chicken shell eggs using radio frequency electromagnetic wave energy to heat the yolk preferably without the use of water.
The dielectric loss factor (∈″) is higher for albumen than for yolk, which means that the albumen will more readily absorb radio frequency energy than the yolk. Nevertheless, because the yolk is located in the center of the egg, the yolk tends to heat faster than the albumen when the egg is rotated with respect to the electric field. In the present invention, the radio frequency electromagnetic wave energy is applied while the eggs are on their side and rotating on rollers while the shell eggs are located between the electrodes. The rollers should be made of a material that does not affect the electric field such as high density polyethylene. A challenge in scaling up a radio frequency shell egg pasteurization process to production levels is achieving uniform heating temperature among the yolks in the large number of shell eggs being pasteurized. The inventors have addressed this issue in several ways. First, the inventors have discovered that it is helpful to move the rotating eggs longitudinally and perpendicularly between the plates while the RF energy is applied.
Second, the radio frequency electromagnetic wave energy is applied in two or more stages in which frequency and/or electric field strength are adjusted to ensure that the yolk temperature does not spike above the desired temperature range for pasteurization (140° F. to 145° F.) In the first stage, the energy may be applied at a frequency (e.g., 27.12 MHz) and electric field strength that efficiently heats the yolk but does not significantly heat the shell, the albumen or other parts of the eggs, e.g. chalaza. A frequency of 27.12 MHz is well suited to provide a uniform electric field across flat plate electrodes. As RF frequency increase, nodes in the electric field are more likely to occur between the plates. It is therefore desirable to use a frequency below about 30-40 MHz. A frequency of 27.12 MHz is also desirable for production scale systems because 27.12 MHz systems are commercially available with sufficient power to meet the heating loads of production scale systems. The voltage between the plates of the RF applicator is regulated, and the electric field strength is typically adjusted by changing the distance between the plates. Energy absorbed is directly proportional to the dielectric loss factor (∈″) and frequency, and exponentially proportional to electric field strength (E2). Therefore, the amount of time to heat the yolk for a given temperature change can be reduced significantly by moving the electrodes closer. On the other hand, setting the electrodes farther apart reduces the rate of energy absorption. Therefore, in accordance with one aspect of the invention, energy is applied at the first stage at a frequency and electric field strength designed to raise the temperature of the yolk to a preselected yolk pasteurization temperature. In the second stage, the energy is applied at either a frequency less than in the first stage or with a weaker electric field in order to maintain the temperature of the yolk at or above the predetermined yolk pasteurization temperature without continuing to raise the yolk temperature above a maximum desired yolk pasteurization temperature. In one embodiment of the invention, the eggs are conveyed through the radio frequency energy applicator preferably on the rollers described above. In the first stage, at 27.12 MHz radio frequency electromagnetic wave energy is applied with the eggs located between parallel plate electrodes. In the second stage, at least one of the parallel plate electrodes is tilted so that the electric field strength decreases as the eggs move through the second stage. Since the shell eggs are rotated as they move through the RF applicator, the yolk absorbs more heat and obtains a higher temperature than the albumen. For example, the yolk can be heated to about 145° F. without noticeably compromising the quality of the yolk. At 145° F., even for a short amount of time, the albumen would coagulate. The advantage of heating the yolk to 145° F. is that the D-value is about 0.45 minutes which means that a full 5-log reduction of Salmonella Enteritidis can occur in less than 2.5 minutes. For the first stage of applying RF energy, the temperature of the yolk should increase to about 145° F. quickly and uniformly in less than 2 minutes. The electric field strength is then decreased in the second stage to lower the amount of energy absorbed by the yolk in order to maintain the temperature of the yolk without further increasing the temperature. This is important for at least two reasons. First, the quality of the yolk can be damaged if the temperature is raised too much above 145° F. Second, if the temperature of the yolk is too high for too long, heat transfer from the yolk will start to coagulate the albumen.
It has also been found desirable to preheat the eggs at, for example 110° F. to 120° F., prior to applying the RF energy to heat the yolks. By preheating the eggs to 120° F., the albumen in the eggs remain substantially unaffected yet the come-up time in the radio frequency applicator is shorter and more efficient thereby providing for more uniformity in heating the egg yolks. Desirably, the preheating occurs in a hot air oven for about 10-15 minutes or less. It may be desirable to preheat the shell eggs in a convection oven set substantially higher than 120° F. in order to accelerate the preheating phase.
After the yolks of the eggs are heated to the preselected pasteurization temperature, e.g. between 140° F. to 150° F. and preferably about 145° F., with the RF energy, the eggs are placed, by conveyor, into an albumen heating environment such as another hot air oven. In one exemplary embodiment of the invention the compartment in which the RF energy is applied, is also an oven. In this way the albumens of the shells in the compartment with the RF applicator are heated similarly to how they are heated in the albumen heating hot air oven, and this reduces the amount of time needed in the albumen heating hot air oven. The albumen heating hot air oven (and if applicable the RF compartment) has a temperature set at a preselected albumen pasteurization temperature, e.g., preferably between 130 to 132° F.; however, it is contemplated that the albumen heating hot air oven can be set at a higher temperature such as 135° F. The eggs are conveyed through the albumen heating hot air oven and are held in that environment for an amount of time sufficient to achieve at least a 5-log kill of Salmonella Enteritidis in the albumen. As mentioned, the D-value for the albumen is much less for a given temperature than for the yolk. For example, as mentioned, the D-value of albumen at 132° F. is about 1.25 minutes. Therefore if the albumen hot air oven is held at 132° F. (and the albumen is maintained at 132° F.), the shell eggs must be held in the oven for 6.25 minutes in order to achieve a 5-log kill of Salmonella Enteritidis in the albumen. As mentioned, the pasteurization process continues in the yolk as long as the temperature of the yolk is maintained above 128° F. Therefore, the accumulation of Salmonella Enteritidis kill in the yolk while the egg is held in the albumen heating hot air oven should also be considered and will reduce the length of heating required in the radio frequency electromagnetic wave energy applicator. In other words, the shell eggs should be held within the albumen heating hot air oven for an amount of time not only sufficient to achieve at least a 5-log kill of Salmonella Enteritidis in the albumen but also sufficient that the combination of heating the yolk with the radio frequency electromagnetic wave energy and holding the shell egg in the albumen heating hot air oven achieves a 5 log kill of Salmonella Enteritidis in the yolk.
One of the advantages of the method described is that it enables pasteurization of chicken shell eggs without the use of water and in a time efficient manner. Further, because relatively low oven temperatures are used, the albumen does not become cloudy or at least significantly cloudy, e.g. 200 nephelometric turbidity units or less. Another advantage of the system is that the pasteurization equipment can be run intermittently and is therefore well-suited for applications with relatively small volumes such as pasteurization operations on the farm site.
The eggs are then conveyed from the RF energy applicator 14 to the albumen heating hot air oven 16. The albumen heating hot air oven is desirably maintained at about 132° F. The purpose of the albumen heating hot air oven is to heat the albumen to and maintain the albumen at a preselected albumen pasteurization temperature for a preselected amount of time in order to achieve at least a 5 log kill of Salmonella Enteritidis in the albumen. The D-value for Salmonella Enteritidis in albumen at 132° F. is about 1.25 minutes. Therefore, the time that the eggs should be in the albumen heating hot air oven 16 is approximately 6-8 minutes.
The plots in
The first compartment 104 is a convection pre-heating oven. The second compartment 106 includes an RF applicator and a convection heater, and the third compartment 108 is a convection albumen heating oven. The in-line pasteurizer 100 uses a recirculation fan 110 to supply air to ducts and heaters for each compartment 104, 106 and 108 independently. The shell eggs travel on the conveyor 102 from left to right in
Still referring to
The second zone 106 is a combination RF applicator and heated hot air zone where the yolk of the eggs are heated internally with RF energy, while the albumen temperature is heated to and maintained at the target temperature, e.g., 132° F. The RF applicator consists of an electrode and matching system that enables uniform electric field heating of the conveyed eggs. The electrode 134 is located above the conveyor 102 in
The recirculation fan 110 moves air through duct 142 and an in-duct electric heater 140 into the second compartment 106 via duct supply vent 146. The duct supply vent 146 is located above the electrode 134 and the conveyor 102 and blows heat air downward on the shell eggs on the conveyor 102 in the second compartment 106. An air valve 144 is provided in duct 142 to adjust the amount of air flow through the duct 142 into the second compartment 106. The electric hot air heater 140 is desirably capable of heating the air in duct 142 to 135° F., although it will normally be operated to heat the second compartment 106 to a temperature of 132° F. in order to minimize cloudiness of the albumen in the shell eggs being pasteurized. A 4.5 kW electric heater 140 is sufficient for the pasteurizer depicted in
The recirculation fan 110 also moves air through duct 152 and an in-duct electric heater 156 into the albumen heating oven 108 via duct supply vent 154. The albumen heating oven 108 is maintained at desirably at the same target temperature as the second compartment 106, e.g., 132° F. The duct supply vent 154 blows heated air downward on the shell eggs on the conveyor 102 in the albumen heating oven 108. The electric hot air heater 156 is desirably capable of heating the air in duct 152 to 135° F., although it will normally be operated to heat the albumen heating oven 108 to a temperature of 132° F. in order to minimize cloudiness of the albumen in the shell eggs being pasteurized. A 4.5 kW electric heater 156 is sufficient for the pasteurizer depicted in
In the foregoing description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred there from beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims. Each limitation in the appended claims is intended to invoke interpretation under 35 U.S.C. §112, sixth paragraph, only if the terms “means for” or “step for” are explicitly recited in the respective limitation.
| Number | Date | Country | |
|---|---|---|---|
| 62157158 | May 2015 | US |
