JP2022001031A - Liquid-food sterilization method using pulse electric field - Google Patents

Abstract

To provide a liquid-food sterilization method using a pulse electric field, capable of performing sufficient sterilization without raising temperature excessively.SOLUTION: A liquid-food sterilization method includes a step A for maintaining temperature at 45°C or higher and below 60°C, a step B for cooling down the temperature at 5°C or higher and below 45°C after the step A, a step C for applying a pulse electric field so that the temperature does not reach 60°C or higher after the step B, and a step D for maintaining the temperature at 53°C or higher and below 60°C after the step C. As such, by performing the step A and the step B before the step C for applying the pulse electric field, and performing the step D after the step C, the sterilization effect can be synergistically enhanced while suppressing the reaching temperature in the step C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for sterilizing liquid foods using a pulsed electric field, which can sufficiently sterilize without excessively raising the temperature.

Conventionally, in the production of liquid foods, a method of heat sterilization is mainly used. However, in liquid foods containing a large amount of protein such as liquid eggs, dairy products, and soymilk, there is a problem that when the sterilization temperature is raised, the flavor is deteriorated due to heat denaturation of the protein. In particular, liquid eggs are more susceptible to heat than other foods. For example, when liquid whole eggs are continuously sterilized, it is necessary to sterilize them at 60 ° C for 3.5 minutes. When sterilization is performed, the egg white protein is denatured, which affects the quality such as deterioration of flavor and physical properties such as foaming property.
Therefore, in the production of liquid foods, it is required to establish a sterilization technique having a sufficient sterilization effect to ensure safety under heating conditions at a lower temperature than before.

From this point of view, a sterilization method using a pulsed electric field is drawing attention. Sterilization by a pulsed electric field utilizes the irreversible perforation phenomenon due to dielectric breakdown of the cell membrane to kill cells, and since it can be sterilized with a relatively simple device, it is expected to be put into practical use in the food field. A sterilization device and a sterilization method using a pulsed electric field are being studied.

As a study so far, for example, Patent Document 1 has a sterilization treatment unit having two electrodes arranged along each other and a liquid substance flowing between the two electrodes, and two electrodes of the sterilization treatment unit. A liquid material provided with a pulse power supply that repeatedly supplies a pulse voltage between them and repeatedly applies a pulse electric field to the liquid material between both electrodes, and a preheater that preliminarily heats the liquid material supplied to the sterilization processing unit. In the sterilizer, the inlet temperature measuring device that measures the temperature immediately before the sterilization process of the liquid material supplied to the sterilization processing unit, the temperature immediately before the sterilization process measured by this inlet temperature measuring device, and the sterilization process of the liquid material in the sterilization processing unit. Using the target value of the after-reaching temperature, the repetition frequency of the pulse voltage supplied from the pulse power supply to the sterilization processing unit, and the optimum repetition frequency at which the reached temperature after sterilization of the liquid material in the sterilization processing unit becomes the target value. Disclosed is a liquid sterilizer comprising a control device for calculating and controlling the repeat frequency of a pulse voltage supplied from a pulse power source to a sterilizer processing unit so as to have the optimum repeat frequency. Further, Patent Document 2 has a plurality of electrodes arranged along each other, and supplies a pulse voltage between the sterilization processing section in which a liquid substance flows between the electrodes and the electrodes of the sterilization treatment section. In a liquid material sterilizer equipped with a pulse power source that applies a pulse electric field to the liquid material between the electrodes, when the sterilizer is started, the liquid material is first circulated at least in a circulation loop including a sterilization processing unit, and then the liquid material is circulated. Disclosed is a method for sterilizing a liquid material, which comprises opening a circulation loop and taking out the sterilized liquid material to the downstream side while sterilizing the liquid material in the sterilization treatment unit.

Japanese Unexamined Patent Publication No. 2000-22175 Japanese Unexamined Patent Publication No. 2000-279146

However, the sterilizing apparatus described in Patent Document 1 and the sterilizing method described in Patent Document 2 are inventions focusing on the step of performing a pulsed electric field itself, and focusing only on the pulsed electric field step is considered in terms of food safety. In order to enhance the sterilizing effect, it is necessary to increase the electric field strength of the pulsed electric field and the number of times it is applied. Physical properties will deteriorate.
The present invention has been made in view of the above points, and an object of the present invention is to provide a method for sterilizing liquid foods using a pulsed electric field, which can sufficiently sterilize without excessively raising the temperature. ..

In view of the above problems, the inventors of the present invention have conducted diligent research. As a result, they have found that the above problems can be solved by devising the pre-process and the post-process of the process of applying the pulse electric field, and have completed the present invention. Specifically, the present invention provides the following.

(1) Step A for holding at 45 ° C. or higher and lower than 60 ° C., step B for cooling to 5 ° C. or higher and lower than 45 ° C. after step A, and a pulse electric field after step B so that the reached temperature does not reach 60 ° C. or higher. A method for sterilizing a liquid food, comprising a step C of applying a step C and a step D of holding the step C at 53 ° C. or higher and lower than 60 ° C. after the step C.
(2) The method for sterilizing a liquid food according to (1), wherein the holding temperature in step A is 45 ° C. or higher and 58 ° C. or lower.
(3) The method for sterilizing a liquid food according to (1) or (2), wherein the temperature reached in step C is 58 ° C. or lower.
(4) The method for sterilizing a liquid food according to any one of (1) to (3), wherein the holding temperature in step D is 53 ° C. or higher and 58 ° C. or lower.
(5) The method for sterilizing a liquid food according to any one of (1) to (4), wherein the temperature in step B is 10 ° C. or higher lower than the temperature in step A.
Is.

In the method for sterilizing liquid foods of the present invention, a step B, which is a cooling step, is provided between a step A, which is a preheating step, and a step C, which applies a pulse electric field. As described above, by cooling to a predetermined temperature before entering the step C, even if a pulsed electric field is applied to the liquid food, the ultimate temperature of the liquid food in the step C can be lowered. Further, in the step A, by keeping the temperature at the above temperature, irreversible denaturation of the cell membrane of the microorganism can be caused, and the bactericidal effect of the step C can be further enhanced. Further, in step D, which is a temperature holding step after step C, holding at the above temperature can promote the killing of sublethal bacteria and synergistically enhance the bactericidal effect of step C. Therefore, according to the present invention, it is possible to provide a method for sterilizing liquid foods using a pulsed electric field, which can sufficiently sterilize without raising the temperature excessively.

It is a figure which shows the process flow about the sterilization method using the pulse electric field of this invention.

Hereinafter, a method for sterilizing a liquid food product according to an embodiment of the present invention will be described.

<Sterilization method of liquid food using pulsed electric field>
FIG. 1 is a drawing showing a process relating to a sterilization method using a pulsed electric field of the present invention. As shown in FIG. 1, the method for sterilizing a liquid food of the present invention includes a step A of holding at 45 ° C. or higher and lower than 60 ° C., a step B of cooling to 5 ° C. or higher and lower than 45 ° C. after step A, and a step B. It has a step C in which a pulse electric field is applied so that the ultimate temperature does not reach 60 ° C. or higher, and a step D in which the pulsed electric field is held at 53 ° C. or higher and lower than 60 ° C. after the step C. In this way, by providing the steps A and B in the pre-process of the step C, which is the step of applying the pulsed electric field, and the step D in the post-step of the step C, the sterilizing effect can be obtained while suppressing the ultimate temperature in the step C. It can be increased synergistically.
A plate-type heat exchanger, a tubular heat exchanger, or the like can be used for heat exchange in each process except step C.

[Process C]
Step C is a step of applying a pulsed electric field so that the ultimate temperature does not reach 60 ° C. or higher, and is an important step that directly contributes to sterilization in the liquid food sterilization method of the present invention. The pulse electric field uses the irreversible perforation phenomenon due to the dielectric breakdown of the cell membrane to necrotize the cells, and the bactericidal effect is enhanced depending on the application intensity and the number of times of application of the pulse electric field. However, when the applied intensity of the pulsed electric field is strong and the number of times of application is large, the Joule heat generated becomes large and the temperature rise of the liquid food becomes large. Therefore, in order to prevent a large temperature rise of the liquid food in the step C, the condition of the pulse electric field in the step C is preferably 10 kV / cm or more and 70 kV / cm or less, and 25 kV / cm or more and 55 kV / cm or less. It is more preferable to have it. Further, the number of times the pulse electric field is applied is preferably 3 times or more and 20 times or less, and more preferably 5 times or more and 15 times or less. The pulse width is preferably 300 ns to 10 μs, more preferably 500 ns to 3 μs. The ultimate temperature in step C is preferably 58 ° C. or lower, preferably 57 ° C. or lower, and 56 ° C. or lower, because liquid foods having excellent flavor and physical characteristics can be obtained by suppressing protein denaturation. It is more preferable to have. Further, although the lower limit is not particularly limited, it is preferably 40 ° C. or higher, and more preferably 45 ° C. or higher, from the viewpoint of sterilization efficiency. For the application of the pulse electric field in the step C, the voltage and the number of times of application can be adjusted within the above range by using the pulse electric field processing tank as shown in FIG.

[Step B]
By setting the conditions of step C as described above, a large temperature rise can be avoided, but a certain temperature rise due to the generation of Joule heat due to the application of the pulse electric field is unavoidable. Therefore, when the temperature of the liquid food immediately before entering the step C is high, the temperature rise in the step C causes the temperature reached by the liquid food to rise. Therefore, in the present invention, a cooling step B is provided between the preheating step A and the step C. In this way, by cooling the liquid food before entering the step C, even if a pulsed electric field is applied to the liquid food, the temperature reached by the liquid food in the step C can be lowered. Further, the temperature in step B is 5 ° C. or higher and lower than 45 ° C., and is preferably 10 ° C. or higher and 40 ° C. or lower in order to reduce the ultimate temperature in step C as much as possible while suppressing the cost due to heat exchange. It is more preferable that the temperature is ℃ or more and 40 ℃ or less. From the viewpoint of the effect of sterilization and the temperature reached in the step C, the temperature of the step B is preferably 10 ° C. or higher lower than the temperature of the step A, and more preferably 15 ° C. or higher.

[Step A]
In the method for sterilizing liquid foods of the present invention, a step A of holding at 45 ° C. or higher and lower than 60 ° C. is provided as a pre-step of step C. In step A, by keeping the temperature at that temperature, deterioration of the flavor, foaming property, etc. of the liquid food can be suppressed, irreversible denaturation of the cell membrane of the microorganism can be caused, and the bactericidal effect of step C can be further enhanced. .. In order to efficiently sterilize without raising the temperature excessively, the temperature in step A is preferably 50 ° C. or higher and 58 ° C. or lower, preferably 50 ° C. or higher and 57 ° C. or lower, and is preferably 50 ° C. It is more preferable that the temperature is 56 ° C. or lower. Further, in order to more effectively enhance the bactericidal effect, the holding time in step A is preferably 5 seconds or more and 120 seconds or less, more preferably 5 seconds or more and 60 seconds or less, and further 5 seconds or more and 20 seconds or less. It is preferably within seconds.

[Step D]
Step D is a step of holding at 53 ° C. or higher and lower than 60 ° C. after step C. By keeping at the temperature, the killing of sublethal bacteria can be promoted and the bactericidal effect of step C can be synergistically enhanced. Further, in order to efficiently sterilize without raising the temperature excessively, the temperature in the step D is preferably 54 ° C. or higher and 58 ° C. or lower, preferably 55 ° C. or higher and 57 ° C. or lower, and 55 ° C. It is more preferable that the temperature is 56 ° C. or lower. In order to enhance the bactericidal effect, the holding time in step D is preferably 10 seconds or more and 600 seconds or less, preferably 30 seconds or more and 300 seconds or less, and further 90 seconds or more and 150 seconds or less. More preferred.

As described above, in the liquid food sterilization method of the present invention, the step C in which the pulsed electric field is applied is adjusted so that a large temperature rise does not occur in the step C, and the step is a step before the step C. By providing step A, which is a subsequent step of step A, step B, and step C, the sterilizing effect can be synergistically enhanced while suppressing the ultimate temperature in step C, so that sterilization can be performed efficiently without excessively raising the temperature. It can be performed.
Further, in the method for sterilizing liquid foods of the present invention, other steps may be performed in addition to the above steps A to D as long as the effects of the present invention are not impaired, but the step of heating at 60 ° C. or higher is performed throughout all the steps. It is preferable not to include, preferably not to include a step of heating above 58 ° C, preferably not to include a step of heating above 57 ° C, and even more preferably not to include a step of heating above 56 ° C. The total processing time of steps A to D is preferably 1 minute or more and 15 minutes or less, and more preferably 2 minutes or more and 10 minutes or less.

[Liquid food]
The liquid food to be the target of the sterilization method of the present invention may be any liquid food that is generally sterilized and distributed, and examples thereof include liquid eggs, soymilk, milk, soup, and sauces. Be done. In particular, in liquid whole eggs and liquid egg whites, protein denaturation progresses by heating at about 60 ° C., and the flavor and functionality deteriorate. Therefore, by using the present invention heated at less than 60 ° C., the flavor and functionality are improved. Is preferable because it can be expected.

Hereinafter, the present invention will be described in detail with reference to examples. The present invention is not limited to the examples shown below.

[Example 1] After the shelled egg was mechanically cracked, the egg yolk and the egg white were stirred with a mixer until they became uniform. Then, Enterobacter (ATCC13048 strain) was added bacteria so that ¹⁰ 7 CFU / ml, and stirred again uniformly, to prepare a liquid whole egg Example 1. Enterobacter (ATCC13048 strain) is the same Gram-negative bacterium as Salmonella, which causes food poisoning due to whole liquid eggs.

The liquid egg of Example 1 above was heated at 55 ° C. for 10 seconds (step A). Next, it was cooled to 30 ° C. (step B). Next, a pulse electric field having a pulse width of 600 ns and an electric field strength of 50 kV / cm was applied until the temperature after application reached 55 ° C. (step C). The number of applications was 5 times. Next, it was heated at 55 ° C. for 120 seconds (step D). The total processing time of steps A to D was about 3 minutes. The number of Enterobacter in the obtained liquid egg of Example 1 was measured, and the number of sterilized eggs was measured. The number of Enterobacter was measured by the following method.

(Measurement of the number of Enterobacter)
The number of Enterobacter was measured by spraying the sample of Example 1 and, if necessary, 10-fold diluted with PBS on a standard agar medium and culturing at 35 ° C. for 1 to 2 days.

[Examples 2 to 10, Comparative Examples 1 to 5]
After preparing the liquid eggs of Examples 2 to 10 and Comparative Examples 1 to 5 in the same manner as in Example 1, sterilization and measurement of the number of bacteria were carried out under the conditions shown in Table 1. The number of times of application of Examples 2 to 10 was in the range of 3 to 20 times. In addition, the time required for steps A to D was the same as that in Example 1. In Table 1, the logarithm of Enterobacter reduced by sterilization is shown as the number of sterilization (digits).

From the results in Table 1, step C is performed in which a pulse electric field is applied so that the temperature of step A is 45 ° C. or higher and lower than 60 ° C., the temperature of step B is 5 ° C. or higher and lower than 45 ° C., and the temperature does not reach 60 ° C. or higher. It was found that the number of bacteria was reduced by 4 orders of magnitude or more when the temperature of step D was 53 ° C. or higher and lower than 60 ° C.
Further, in particular, the temperature of step A is 50 ° C. or higher and lower than 60 ° C., the temperature of step B is 10 ° C. or higher and 40 ° C. or lower, and the temperature of step D is 54 ° C. or higher and lower than 60 ° C., so that the number of bacteria is increased. It was found that a strong bactericidal effect that was reduced by 5 orders of magnitude or more could be obtained.

[Reference Example 1]
To confirm the effect of the conventional sterilization method, the liquid eggs prepared by adding Enterobacter in the same manner as in Example 1 were heated at 55 ° C. for about 3 minutes without performing steps B to D. .. The number of bacteria decreased was 1.5 digits.

[Example 11] A liquid egg of Example 11 was prepared by the same method as in Example 1 except that the temperatures of Steps A, C, and D were changed to 56 ° C. The number of bacteria decreased was more than 5 digits.

From the above, according to the method for sterilizing liquid foods of the present invention, sufficient sterilization can be performed without excessively raising the temperature.

Claims (5)

Step A of holding at 45 ° C or higher and lower than 60 ° C, and
Step B, which cools to 5 ° C or higher and lower than 45 ° C after step A,
After step B, step C in which a pulsed electric field is applied so that the reached temperature does not exceed 60 ° C.
A method for sterilizing a liquid food, comprising step D, which is held at 53 ° C. or higher and lower than 60 ° C. after step C. The method for sterilizing a liquid food according to claim 1, wherein the holding temperature in step A is 45 ° C. or higher and 58 ° C. or lower. The method for sterilizing a liquid food according to claim 1 or 2, wherein the temperature reached in step C is 58 ° C. or lower. The method for sterilizing a liquid food according to any one of claims 1 to 3, wherein the holding temperature in step D is 53 ° C. or higher and 58 ° C. or lower. The method for sterilizing a liquid food according to any one of claims 1 to 4, wherein the temperature in step B is 10 ° C. or higher lower than the temperature in step A.

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