JP4516860B2 - Liquid food sterilization apparatus and sterilization method - Google Patents

Description

  The present invention relates to a technique for sterilizing microorganisms that are problematic in soft drinks such as fruit juices, coffee drinks, tea drinks, milk-containing drinks, soups, alcoholic drinks, dashi and other various liquid foods. According to the present invention, it has become possible to easily sterilize heat-resistant spore bacteria that could not be easily sterilized in the past. Therefore, the present invention is particularly useful for further improving the safety and storage stability of liquid foods. It is.

  Conventionally, in the industry, in order to sterilize microorganisms, it is common to sterilize by heating an object to be processed. From the viewpoint of controlling microorganisms, microorganisms are controlled by using antibacterial agents, bacteriostatic agents, etc., or adjusting pH. Moreover, in recent years when the use of food additives is not preferred, interest in physical or electrical sterilization methods has increased, and for example, a method using a high voltage pulse has been proposed (see Non-Patent Document 1). .

Sure, this high voltage pulse method is an excellent method, but it is necessary to store the sterilization target in the tank once. Deterioration of flavor and quality is inevitable, and it is hard to say that it is fully satisfactory.
Journal of Japan Society for Food Engineering, Vol. 4, no. 2, p47-51 (June 15, 2003)

  The present invention effectively sterilizes microorganisms (including heat-resistant spore bacteria) that cause problems such as spoilage and deterioration in foods, improves the shelf life of foods, and the amount of additives used for microorganism control The purpose is to prevent or suppress heat deterioration due to reduction of heat and heat sterilization, for example, prevention or suppression of decomposition of active ingredients and aromas.

  The present invention has been made to achieve the above object, and as a result of examination from various directions, attention has been paid to an electrical method, not a chemical method, and prevention of changes in active ingredients associated with heating of food. When an electric field is generated by applying a voltage using an AC power source, aiming at prevention and control of changes in fragrance components, control, fragrance components, and reduction of various additives for microbial control, changes in the above effective components and fragrance components For the first time, it was found that heat-resistant spore bacteria that can effectively sterilize microorganisms more effectively and can be effectively sterilized in a short time can be effectively sterilized. As a result of further research, the present invention has finally been completed.

  That is, the present invention is a method for sterilizing a liquid food having electrical conductivity using an energization unit sandwiched between one or more pairs of metal electrodes, wherein an AC power source is connected to the electrode of the energization unit, and the voltage The present invention provides a method for sterilizing liquid food, characterized in that microorganisms are sterilized by continuously passing the liquid food through a current-carrying unit to which is applied.

  More preferably, in the present invention, at least the energization unit is a closed system, and the inside thereof includes sterilizing the liquid food while pressurizing it, and the closed system energization unit is included. It is also included as one embodiment that the internal pressurization is due to the liquid food itself passing through it.

  In order to carry out the above method, it is desirable to provide a food production line with an energization unit in a container provided with a liquid supply port and an extraction port, the energization unit has a metal electrode, and pressurizes the inside of the energization unit. . By passing liquid food through the energization unit to which such a voltage is applied, an electric field is generated between the electrodes, and microorganisms can be sterilized.

The present invention also provides an apparatus for carrying out the above method, and one of the embodiments includes the following apparatus.
(Aspect 1)
The liquid supply port and the liquid discharge port are connected to an energization unit, and a pair of metal electrodes are arranged on the energization unit, and an AC power source is connected to these electrodes to generate an electric field between the electrodes. A continuous sterilization apparatus for liquid food, characterized in that the inside of the energization unit can be pressurized.

(Aspect 2)
It is provided with a liquid feeding means, an energizing unit, a cooling device, and a pressure holding valve. The energizing unit is provided with one or more pairs of metal electrodes, and an AC power source is connected to these electrodes, and preferably at least A continuous sterilization apparatus for liquid food, characterized in that a liquid means, a current-carrying unit, a cooling device, and a pressure holding valve are connected to form a sealed system.

(Aspect 3)
The apparatus according to aspect 2, wherein a preheating device is installed in front of the energization unit, and the preheating device is a heating heat exchange plate and / or an energization unit.

(Aspect 4)
The apparatus according to aspect 2 or 3, wherein the cooling device is a heat exchange plate or a tube for cooling.

(Aspect 5)
5. The apparatus according to any one of aspects 1 to 4, wherein the energization unit is formed by pressurizing the inside thereof with a liquid to be fed or the like without being accommodated in the pressurized container.

  According to the present invention, the liquid food can be sterilized continuously by passing the liquid food through the electric field in the energization unit. In addition, at least the inside of the current-carrying unit can be pressurized to sterilize not only ordinary microorganisms but also heat-resistant microorganisms, especially heat-resistant spore bacteria within 1 second, so that the flavor and quality of liquid foods can be reduced. It is possible to prevent the deterioration of the active ingredient, the decrease in the active ingredient, and the alteration, and it is particularly suitable as a liquid food sterilization system.

  In addition, from the standpoint of the device, each device and means in addition to the current-carrying unit are connected by pipes and become a sealed system, so that their interior is pressurized by the pressure of the liquid food itself fed by the pump. It is not necessary to house the entire apparatus in a pressure vessel, the apparatus is compact, the operation is greatly simplified, and sterilization can be achieved very efficiently.

  Liquid foods, especially liquid foods in containers such as canned juices and canned coffee drinks, are often sold in vending machines and are consumed after a certain period of time. If heat-resistant spore bacteria remain, they propagate during this period, resulting in spoilage and quality degradation. However, in order to completely sterilize such microorganisms, it must be treated at a high temperature and high pressure for a long time, and an increase in cost, flavor of liquid food, and deterioration of quality are inevitable.

  The present invention has been successful for the first time to solve these problems all at once, and is a sterilization method particularly suited to the technical field of food and drink. In addition, since it is not necessary to use a large and complicated pressurizing device, it is excellent in terms of cost, operation and work safety, and it can be used for food and beverages in that a very high sterilizing effect can be obtained with a small device. It is particularly outstanding as a product sterilization system.

  In the present invention, an electric field is generated between electrodes by passing a liquid food through an energization unit to which a voltage is applied, and microorganisms are continuously sterilized. Accordingly, by further pressurizing the inside of the energization unit, the heat-resistant spore bacteria that have been difficult to sterilize in liquid can be sterilized in a very short time, and a significant increase in efficiency is achieved.

The continuous sterilization method according to the present invention can be carried out with an apparatus as exemplified below.
The liquid supply port and the liquid discharge port are connected to an energization unit, and a pair of metal electrodes are arranged on the energization unit, and an AC power source is connected to these electrodes to generate an electric field between the electrodes. A continuous sterilization apparatus for liquid food, characterized in that the inside of the energizing unit can be pressurized.

  The inside of the energizing unit may be an open system, but the inside of the energizing unit can be pressurized by using a sealed system. The energization unit can be pressurized without accommodating the energization unit in a pressurized container by making itself a sealed system. For example, since the energization unit is hermetically sealed, a pressurized gas may be supplied into the energization unit, or the pressurized state can be achieved only by the pressure of the liquid that is passed through the energization unit by a pump.

  Hereinafter, the present invention will be described more specifically with reference to the accompanying drawings.

  FIG. 1 illustrates an embodiment of a liquid food sterilization apparatus according to the present invention. The upper part is a first example, and the lower part is a second example.

  As shown in FIG. 1, the continuous sterilization apparatus for liquid food according to the present invention includes a liquid feeding means, a (preheating device), an energizing unit, a cooling device, and a pressure holding valve, and the energizing unit includes one or more pairs of metals. These electrodes are provided with an AC power supply, and at least a preheating device, a power supply unit, a cooling device, and a pressure holding valve are connected to form a sealed system. When heating is necessary in advance for sterilization, a preheating device may be used.

  More specifically, for example, a pump is used as the liquid feeding means, and it is appropriately selected from a commonly used plunger pump, cylinder pump, rotary pump, etc., and a heat exchange plate (heating) is used as the preheating device. For example, as in the second embodiment (lower stage), an energizing unit may be provided to use the Joule heat.

  The energization unit (indicated as a high electric field electrode in the drawing) is formed with a channel through which the liquid supplied from the liquid supply port flows, and this channel is at least connected to an AC power source (high frequency AC power source). It has a configuration with a pair of electrodes facing it. Specifically, an AC power source is connected to the electrodes of the energization unit, and the electrodes to be connected can be sterilized by adopting a configuration in which at least one pair of metal electrodes covered with an insulator is faced. Further, the insulator covering the electrode is in a sealed state so that it can be pressurized.

  As the type of electrode, there is no problem as long as it is a metal having electrical conductivity, but in order to prevent deterioration such as corrosion of the electrode, titanium, platinum or stainless steel is desirable. In addition, a plurality of electrodes can be stacked by stacking a plurality of insulators on the electrodes of the energization unit.

  Since the liquid food is heated by the Joule heat by performing the energization process in the energization unit, flavor and quality deterioration occur. Therefore, if it is not desired, a cooling means may be provided, for example, a heat exchange plate (cooling plate) Can be used.

  The liquid food sterilized in this way is taken out of the system through a pressure holding valve (pressure regulating valve). The pressure adjustment is adjusted by the liquid feeding means and the pressure holding valve to maintain an appropriate state in the energizing unit.

  The continuous sterilization apparatus according to the present invention is thus connected by piping (pipe: indicated by a black arrow in the figure) from the pump to the pressure holding valve, and itself constitutes a sealed system. Therefore, the preheating means to the pressure holding valve, at least the energizing unit, can be pressurized by itself without being arranged in the pressurized container, so this apparatus is installed in an open space. However, it is very characteristic and efficient in that the high pressure electric field sterilization treatment under pressure can be performed. That is, this is fundamentally different from the case where the energization unit is housed in the pressurization container and the energization unit is pressurized from the outside.

  Unlike the case where this device is newly housed in a pressurized container by adopting such a configuration, each device and means are connected by a pipe, so that pressure control is easy. Fine adjustment is also possible. As the pressurizing means, pressurized gas may be used, and the water pressure (hydraulic pressure) of the liquid food itself can be used. Therefore, by controlling the pump (and holding valve if necessary), it is exceptional. Without providing a separate pressurizing means, the pressurized state can be obtained by utilizing the water pressure of the liquid food, and this apparatus can be said to be a self-contained apparatus. The pressurizing means is preferably water pressure (hydraulic pressure), and when a pressurized gas is used, the pressure during the treatment can be kept constant.

  In order to sterilize liquid food, first, liquid food (unsterilized material) is passed through a pump, preheated, then treated with a current-carrying unit, then cooled, and sterilized through a pressure holding valve. The present invention may be taken out to the outside, but in the following, the present invention will be described in detail by taking the case where the inside is pressurized as an example.

  Liquid food (after preheating) is energized under pressure in the energizing unit, but when the pressure in the energizing unit adds 40 ° C to the product temperature when voltage is applied to the liquid food It is desirable that the pressure be equal to or higher than the saturated water vapor pressure. The reason is that by suppressing the spark (a phenomenon in which discharge is temporarily generated) that is likely to occur when the liquid food that is passed through contacts the electrode, it is possible to efficiently achieve microbial sterilization and to prevent microspark. This is to prevent deterioration of the material. The pressure is 0.6 MPa or more, preferably 0.8 MPa or more, and more preferably 0.9 MPa or more at 120 ° C., and the addition value may be determined according to this.

  The voltage application time of the electrodes in the overpower unit is very short and should be within 1 second. This is because if the voltage application time is too long, a sufficient applied voltage cannot be secured. Thus, the application time is within 1 second, preferably within 0.5 seconds, and in the examples, it is exemplified within 0.05 seconds, such as 0.006 to 0.044 seconds. Thus, in the present invention, the voltage application time is within 1 second, for example, within 0.1 second, which is very characteristic in that it is extremely short.

  Regarding the relationship between the distance between electrodes, applied voltage, and voltage application time, the applied voltage (V / cm) to the electrode per 1 cm distance between the electrodes and the voltage application time to the liquid food (the passage time of the liquid food) It is desirable that the integration coefficient of (seconds) is 50 or more. This relationship is because when the coefficient is 50 or more, sterilization of microorganisms can be achieved more than normal heat sterilization (such as UHT sterilization and retort sterilization). This coefficient may be 50 or more, and there is no particular limit, but usually 60 to 200 is exemplified. These relationships are represented by mathematical formulas as follows.

Applied voltage per electrode distance (V / cm) × application time (seconds) ≧ 50
(In the formula, V represents voltage, and cm represents the distance between the electrodes.)

  Further, in the present invention, there is no problem even if the energization unit is passed through the energization unit twice or more, or a preheated plate using a heat exchange plate or the like is passed through the energization unit. In FIG. 1, the apparatus of the present invention is shown as a horizontal type, but a solid type can also be used.

  The frequency of the power source is 50 kHz or less, preferably 20 kHz or less, preferably 10 to 20 kHz from the viewpoint of energy efficiency and corrosion resistance with respect to the electrode, and 5 kHz or less can also be used.

  The microorganisms that can be sterilized by the present invention are microorganisms that require heat sterilization, and are particularly suitable for microorganisms that cause deterioration or decay. Furthermore, sterilization by the method of the present invention is effective for heat-resistant microorganisms that require sufficient sterilization even by heat sterilization and microorganisms that form spores. For example, Bacillus genus, Geobacillus genus, Alicyclobacillus genus, Morella genus, Clostridium genus, Thermoanaerobacter genus and the like centering on Gram-positive bacteria are exemplified.

  Furthermore, since the liquid food is heated by generating resistance heating (Joule heat) when energized, the liquid food is immediately passed through the energizing unit so that excessive heat is not applied. It is desirable that the structure be cooled.

  Examples of foods that can be passed are fruit juice, vegetable juice, milk, soy milk, soup, various soft drinks, coffee drinks, tea drinks, alcohol, dashi, and soup.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
Preparation of microorganisms Spore formation was performed in a normal bouillon medium manufactured by Eiken Equipment Co., Ltd. using thermostable microorganism spores Bacillus subtilis JCM2477, and the formed spores were stored in 0.85% physiological saline containing 10% glycerol, and kept at −85 ° C. The frozen product was used as a microorganism.

Effect of pressure 0.01% sodium chloride is used to impart electrical conductivity by pressurizing the inside of the energizing unit to 0.4, 0.6, 0.8, 0.95 MPa using the above-mentioned microorganisms using the apparatus of FIG. A suspension of microorganisms in water was passed through. The electrodes used were 6 mm (width) x 32 mm (height) x 1 mm gap between electrodes and 6 mm (width) x 16 mm (height) x 1 mm gap between electrodes, and using a pump, the flow rate was 1 L / min. Liquid. The AC electric field application time of each electrode was 0.011 seconds and 0.006 seconds, and the applied electric field was 8000 V / cm and 8500 V / cm (frequency 20 kHz). The product temperature at that time was 115 ° C. It cools to normal temperature within 1 second after a process, and it shows by the number of surviving bacteria (logarithm)-initial spore bacteria number (logarithm) (FIG. 2). The positive value of this value indicates the number of dead sterilization.

  The number of remaining microbial spores was measured by counting the number of colonies on a standard agar medium made by Eiken Equipment. From the above results, it is possible to increase the pressure by adding 40 ° C. to 115 ° C. (vapor pressure 0.7 MPa) to 0.45 MPa or higher. It has been found that subtilis spores can be efficiently sterilized.

(Example 2)
Effect of applied electric field time and applied voltage The inside of the energizing unit was pressurized to 0.9 MPa using the microorganisms used in Example 1, and the electrodes used were 6 mm (width) × 32 mm (height) × interelectrode spacing 1 mm, 2 mm and The liquid was passed at a frequency of 20 kHz and a flow rate of 1 L / min using 4 mm and 6 mm (width) × 24 mm (height) × interelectrode spacing of 2 mm and 4 mm. The AC electric field application time for each electrode is shown in Table 1 below.

* Applied voltage The values outside () are applied voltage per 1 mm (V / mm)
Numbers in parentheses Applied voltage during actual test (V)

  Moreover, in order to change the applied electric field strength, the treatment was performed while changing the saline concentration when passing through the solution to 0.01 to 0.2%. The product temperature at that time was 115 ° C. It cools to normal temperature within 1 second after a process, and shows by the numerical value which deducted the number of initial spore bacteria from the number of survival bacteria (FIG. 3). In Table 1 and FIG. 3, the circled numbers correspond to each other.

The number of remaining microbial spores was measured by counting the number of colonies on a standard agar medium made by Eiken Equipment. In addition, the B. Since D115 ° C. = 0.029 in a subtilis bath (ie, Death Value (D value) at 115 ° C. is 0.029 minutes), the number of bacteria that can be sterilized in 1 second (logarithm) is 0.57. Therefore, by setting the coefficient to 50 or more, It has been found that subtilis spores can be effectively sterilized.

1 shows a continuous sterilization apparatus according to the present invention. The relationship between processing pressure and the number of germicidal bacteria is shown. The relationship between the electrode used and the number of germicidal bacteria is shown.

Claims (3)

Parallel plates faced in a pair of metal (width) x (height) x (inter-electrode spacing) covered with an insulator that is sealed so that the liquid flow path can be pressurized internally A method for sterilizing electrically conductive liquid food using an energization unit sandwiched between electrodes, wherein an AC power source is connected to the electrode, the energization unit is a sealed system, and the energization unit is placed in a pressurized container. While applying pressure to 0.45 to 0.95 MPa by the liquid food itself that is fed without being stored, the electric field application time of the electrode in the energization unit to the energization unit to which voltage was applied (electrode passage time of liquid food) ) For 0.006 to 0.044 seconds, the liquid food is continuously passed, the applied voltage (V / cm) to the electrode per 1 cm distance between electrodes and the electric field application time to the liquid food (electrode for liquid food) The accumulated number of (passing time) (seconds) is 50 or more A method for sterilizing liquid food, characterized by sterilizing heat-resistant spore bacteria.
Applied voltage per electrode distance (V / cm) × application time (seconds) ≧ 50
(In the formula, V represents voltage, and cm represents the distance between the electrodes.)   Using a current-carrying unit sandwiched between a pair of metal parallel plate electrodes covered with an insulator that is sealed so that the liquid flow path can be internally pressurized, The method according to claim 1, wherein the method is a sterilization method.   A method for producing a sterilized liquid food comprising sterilizing heat-resistant spore bacteria by the method according to claim 1 or 2.

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