JPH0398565A - Sterilization method for liquid foods - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Background of the Invention] Industrial Application Fields The present invention provides a method for sterilizing liquid foods (foods at the product stage, and liquids including raw materials and semi-finished products thereof). Regarding. More specifically, the present invention relates to a method of sterilizing germs in liquid foods by applying high-voltage electric field pulses.

Prior Art> One of the most important points to keep in mind when manufacturing liquid foods is to prevent contamination by germs.

Methods for preventing bacterial contamination of liquid foods, ie, liquid foods including raw materials, semi-finished products, and finished products, generally include heat sterilization methods and filter sterilization methods.

However, when heat sterilization methods attempt to obtain a satisfactory sterilization effect, the quality of liquid foods deteriorates due to the heat. In addition, the sterilization method using a filter has problems with its lifespan due to clogging of the filter.

Therefore, in order to sterilize using energy efficiently, methods of sterilization by applying DC voltage or AC voltage to liquid foods have been considered, but in both cases, sterilization is performed by the products of electrode reactions. The basic principle is that it is difficult to apply to food.

In addition, although the sterilization method using underwater pulsed discharge shock waves has good energy efficiency, there are also problems with the mechanical strength of the food containers used during sterilization, the amount of noise, and the liquid to be sterilized due to metals eluted from the electrodes. There are disadvantages such as contamination of liquid foods.

On the other hand, the sterilization method by applying a pulsed electric field is described in the specification of Japanese Patent Application No. 154825/1982 ("Sterilization method in an environment of immobilized biocatalyst") and Japanese Patent Application No. 252531/1988 ("Method of sterilization of beverages") filed by the present applicant. ”) as stated in the specification,
Although it has advantages such as being able to selectively kill only the bacteria surrounding the immobilized biocatalyst and having no effect on the flavor of the beverage, it was not possible to expect a significant reduction in the number of viable bacteria.

Furthermore, the method of Sakurauchi et al. (Yujiro Sakurauchi, Eiaki Kondo: “On the bactericidal effect of high-voltage electric field on microorganisms” Journal of the Japanese Society of Agricultural Chemistry, vol. 54, NQ. 10, pp. 837 -
844, 1980), and the method of Safe et al.
J. H. Sale andW. A. Hallilt
on. ．． Effects of high el0c
tricfelds on ifcroorgan1
sms. ．． Blochlts. Blophys. A
cta. 14B, pp. ysx-goo 1987
) also requires a large amount of power using an extremely large capacitor, making it difficult to put it into practical use on an industrial scale, and the sterilizing effect is not sufficient.

[Summary of the invention]

<Summary> The purpose of the present invention is to solve the above-mentioned problems and provide a method that can significantly reduce the number of viable bacteria in liquid foods even by using a low-power pulsed electric field. This objective is achieved by imparting a stirring action to liquid foods.

That is, in the method for sterilizing liquid foods according to the present invention, the electric field strength during pulse application is 2 to 100 kV/cm, the rise time of the pulse waveform is 20 nsec to 1 μsec, and the width of the pulse waveform is 100 nsec to 1 msec. In the sterilization of liquid food by applying a high-voltage electric field pulse, the invention is characterized in that a stirring action is imparted to the liquid food.

Effect> If a high-voltage electric field pulse is applied to a liquid food under the application conditions according to the present invention as described above, and a stirring action is given to the liquid food before or after the pulse is applied, or at the time of the pulse application, the electric field fluctuation due to the pulse is , and the generation of turbulent flow due to the stirring action, resulting in greater damage to microorganisms in liquid foods (e.g., damage to cell membranes and cell walls).
selectively given. On the other hand, the various non-microbial components (proteins, carbohydrates, vitamins, etc.) in liquid foods are not substantially affected by this pulse and stirring action.

Effects> According to the sterilization method of the present invention, the synergistic effect of the application of high voltage pulses and the stirring action makes it possible to sterilize germs in liquid foods with low electric power without deteriorating the quality of these foods. can.

[Specific description of the invention]

In the method for sterilizing liquid foods according to the present invention, the electric field strength during pulse application is 2 to 100 kV/e+n, the rise time of the pulse waveform is 20 nsec to 1 μSl3e%, and the width of the pulse waveform is 100 nsec to 1 msec. As described above, the method for sterilizing liquid food by applying a high-voltage electric field pulse is characterized by imparting a stirring action to the liquid food.

Furthermore, the sterilization method according to the present invention can be applied not only to liquid foods but also to sterilization of microorganisms, limb-shaped media for culturing animal and plant cells, liquid medicines, and water and sewage.

<Liquid Food> The liquid food as used in the present invention refers to raw materials, semi-finished products, and finished products of liquid, fluid, or semi-liquid foods. Examples of such items include alcoholic beverages such as beer or wine, soft drinks, mayonnaise, tomato puree, retort foods, soy sauces, lactic acid drinks, milk, liquid dairy products, oils, coffee drinks, and liquid seasonings. etc., as well as their raw materials and manufacturing intermediates.

<Sterilization by application of high-voltage electric field pulses and stirring action> By applying a high-voltage electric field pulse to the above-mentioned liquid food and giving the liquid food a stirring action before, after, or during the pulse application, the limb-shaped food can be sterilized. To more reliably kill germs in the liquid without altering its quality (for example, protein denaturation, chemical change, etc.).

(1) Application of high-voltage electric field pulses Application of high-voltage electric field pulses is usually performed by applying high voltage to electrodes immersed in liquid food using a discharge switch so that a predetermined electric field strength is achieved. .

Any method can be used for this purpose, but for example, a sterilization tank having coaxial double cylindrical electrodes as shown in FIGS. 3 and 4, or a sterilization tank as shown in FIG. Using a sterilization tank with electrodes on each opposing side wall of a flow path bent in a reciprocating manner, a high-voltage electric field pulse is applied between both electrodes, and liquid food is continuously supplied between the electrodes to sterilize. It can be performed.

Furthermore, if a substantially cylindrical box-shaped sterilization tank having electrodes on opposite side walls as shown in FIG. 5 is used, a batch sterilization method for liquid foods can be achieved.

(a) High-voltage electric field pulse The high-voltage electric field pulse used in this invention has a maximum electric field strength between electrodes of 2 kV/am to 100 kV/am when applied.
cm, when the voltage between the electrodes at that time is monitored with an oscilloscope, the pulse waveform (waveform showing temporal changes in voltage) has an extremely fast rise of about 20 nSeC to 1 μSeC, and a high-speed pulse with a width of about 100 nSeC to 1 nsec. (or a short pulse). This fast pulse is obtained by discharging the capacitor charging energy over a short period of time through a discharge switch.

As a discharge switch, static gap, rotating gap,
Thyrisk, Thyratron, etc. can be used. Ordinary aqueous solutions contain large amounts of ions and are good electrical conductors, so when a DC voltage is applied to the immersed electrodes, a large current flows and electrolysis occurs.

However, when a pulse like the one described above is applied, the electrons run at high speed, but the ions that carry the current move slowly, so the aqueous solution exhibits properties similar to electrically insulating liquids. That is, it is characterized by being able to create a field with high electric field strength in a conductive aqueous solution [Masayuki Sato et al.: Collection of Abstracts of the Gunma Convention of the Society of Chemical Engineers (1988), p. 213). Note that the polarity of the high-voltage electric field pulse can be positive or negative, and both can be used in the present invention.

(Example) Electrode The type of electrode (e.g., platinum, stainless steel, graphite, etc.) can be selected as long as the desired high-voltage electric field pulse can be applied.
There are no restrictions on the shape (for example, cylindrical, plate-like, wire-like, needle-like), size, or immersion position (for example, the distance between electrodes). However, since sterilization is actually carried out only in the area where the high-voltage electric field pulse is applied between the electrodes, these conditions must be selected so as to obtain the desired sterilization effect.

(c) Conditions for application of high-voltage electric field pulses In order to obtain the desired sterilization effect by applying the high-voltage electric field pulses specified in (a) and applying the stirring action described below, various application conditions, such as the number of applied pulses, etc. Set. It is known that the killing characteristics of ban yeast by applying high-voltage electric field pulses are approximated to the Weidel distribution [Akira Mizuno et al.: Abstracts of the Gunma Conference of the Society of Chemical Engineers (1988), p. 211 and Akira Mizuno et al.: Collection of Abstracts of National Conference of the Institute of Electrical Engineers of Japan (1986) p. 709). According to this, the application conditions can be determined in advance by determining the bactericidal effect against each target germ in a preliminary experiment, and the results can be derived using an experimental formula, so the various conditions to obtain the desired bactericidal effect can be determined using that formula. It can be set arbitrarily within the range.

One preferred example of the above-mentioned high-voltage electric field pulse generator is shown in a schematic diagram (electric circuit diagram) in FIG.

In this device, an ACIOOV power supply (50 Hz) is voltage-regulated by a slider 1, then boosted by a high-voltage transformer 2, and rectified by a high-voltage diode 3. The electric charge charged in the capacitor 5 through the charging resistor 4 is discharged by electrical connection of the spark gap 6, and a high voltage electric field pulse is applied in the sterilization tank 7.

The pulse waveform can be observed using an oscilloscope 9 through the high-pressure probe 8.

(2) Providing stirring action As mentioned above, stirring action can be applied to liquid foods before, after, or at the time of application of the high voltage pulse, and it may be applied at any one of these times or at multiple times as necessary. You can also combine them. The application of the high voltage electric field pulse and the operation of the stirring action may be performed at the same time, or
Both may be repeated alternately.

Any method suitable for the purpose can be used as a method for imparting a stirring action, and the following methods are representative examples thereof.

(a) A magnetic stirrer is placed in a sterilization tank containing liquid food and a rotating magnetic field is applied from the outside.

(b) Stir the liquid food in the sterilization tank with a stirrer #S (for example, a glass rod) or use a pipette to perform suction and discharge operations.

(c) A sterilization tank having a reciprocatingly curved channel is used to cause a change in flow (turbulence, etc.) in the liquid food at the curved portion of the channel (see Figure 2).

(2) Providing a protruding plate part inclined in the flow direction in the flow path to cause a change in the flow of the liquid (for example, providing a protruding plate part 11 in the straight flow path part of the sterilization tank shown in FIG. 2) ).

(E) The width of the flow path is changed by providing a narrow portion and a wide portion in the flow path, thereby stirring the liquid hydrodynamically and causing a change in the flow of this liquid (for example, as shown in Fig. 4). As shown in Figure 2, the outer peripheral surface of the inner cylindrical electrode of a sterilization tank having coaxial double cylindrical electrodes can be provided with spiral or ring-shaped irregularities arranged at appropriate intervals).

(F) By supplying liquid food at a faster flow rate to a coaxial double cylindrical continuous sterilization tank as shown in FIG. 3, a change in flow is caused in the food liquid.

By using a combination of the high-voltage electric field pulse and stirring action as described above, and determining the sterilizing effect on each target germ in advance with respect to the pulse application conditions and stirring conditions, the results can be derived using an empirical formula. Conditions for obtaining the desired bactericidal effect can be arbitrarily set within the range of the formula.

If the distance between the electrodes is shortened, it is possible to apply pulses with smaller electric power, but in the present invention, which provides a stirring action, a greater sterilizing effect can be obtained even with a small electric power pulsed electric field. Brewer's yeast (S.c.
Fig. 9 shows the form of the ``erevjsiae''.

Experimental Examples> Example 1: An experiment was conducted to examine the relationship between the number of pulses applied when high-voltage electric field pulses were applied, the presence or absence of stirring action, and the number of surviving microorganisms. Here, as shown in FIG. 5, sterilization was carried out in a substantially cylindrical box-shaped sterilization tank using the system shown in the schematic diagram of the electric circuit shown in FIG. In FIG. 5, 21 is an electrode on both sides, 22 and 24 are transparent acrylic plates, 23 is a transparent acrylic tube, 25 is a part connected to ground, and 30 is an injection port made of a transparent acrylic tube.

(1) Conditions O Sterilization tank: Content capacity 15ml (Fig. 5) Electrode 2 circular parallel electrodes (made of stainless steel) O sample: Beer O Bacteria to be sterilized: S. cerevlslae IPO
02590 Initial number of bacteria: Approximately 1 07 cells/mlO
Electric field strength = 20kv/cffl O capacitor capacity 20. 004 μF O pulse period: 20 msec (2) Experimental method Every time a high-voltage electric field pulse was applied 1200 times (approximately 24 seconds each), the sample in the sterilization tank was stirred (suction and discharge operations) three times (near both electrodes). and center) to determine the relationship between the number of pulses applied and the number of viable bacteria.

(3) Experimental results As shown in Figure 6, in the pulse application method without stirring,
For a viable cell count of about 10' cells/ml at most, the stirring method has a 10' eel Is
The number of viable bacteria decreased to 1/ml.

Example 2: Using a substantially box-shaped killing tank as shown in FIG. 7, sterilization is carried out using the system shown in the electrical circuit schematic diagram shown in FIG. 2 in the diagram
6 and 27 are both electrodes, 28 is a transparent acrylic plate, 29
is the part connected to ground.

(1) Sterilization conditions Tank: Horizontal type (Fig. 7) Sample liquid: Distilled water Target bacteria for sterilization: Yeast (S. cerevls 1ae) Initial number of bacteria: approx. 107eel Is/ml Electric field strength: 30
kV/c+n Capacitor capacity ffi:O. OO4μF Pulse period: 20ffls (2) Experimental method After applying a high-voltage electric field pulse 1200 times (about 24 seconds), the sample liquid is taken out from the sterilization tank, and the operation of injecting it again and applying the pulse is repeated 4 times.

(3) Experimental results When the initial number of viable bacteria was 107eel Is/ml, there was a significant decrease in the number of viable bacteria to approximately 4 x 102cells/ml after the experiment.

Example 3: Sterilization is carried out using the continuous sterilization tank shown in FIG. 2 and the system shown in the electrical circuit schematic diagram shown in FIG. 1. In the figure, 10 is both electrodes, and 11 is a protruding plate portion.

(1) Sterilization under various conditions Tank: Continuous sterilization tank shown in Figure 2, capacity of one tank 60ml Sample liquid: Distilled water Enterobacter aeroge to be sterilized
Initial number of ncs bacteria: Approximately 105eel Is/ml Electric field strength: 30kV/cm Capacitor capacity: 0.012μF Pulse period: 100ms (2) Experimental method 1> Fill the sterilization container with the sample liquid and apply 4800 pulses. After that, remove the sample.

2> Repeat 4 times to operate the pump to move about 60 ml of sample liquid every 1200 pulses, and take out the sample with the same residence time as in 1).

(3) Experimental results When the initial number of bacteria is 10” cells/ml, 1)
2) is about 5 x 10' cells/ml, whereas in 2) it is about 5 x 10' cells/ml.
A significant decrease in the number of viable bacteria was observed.

Example 4: Sterilization is carried out using the continuous sterilization tank shown in FIG. 4 and the system shown in the electrical circuit schematic diagram shown in FIG. In the figure, 19 is an inner tube electrode, and 20 is an outer tube electrode.

(1) Sterilization conditions Sterilization Hinoki: As shown in Figure 4, cylindrical shape with a capacity of 500 ml, spacing between electrodes 3 to 5 mm Sample liquid: Beer Bacteria to be sterilized: S. Initial number of C. ccrevislae bacteria: Approximately 107 cells/ml Electric field strength: 40 kV/a
m Capacitance: 0.05μF Pulse period: 5001S (2) Experimental method 1) A sterilization tank is filled with a sample liquid and a pulse is applied 7200 times, after which a sample is collected.

2> Collect the sample while continuously injecting and discharging the sample liquid at 83 ml/min using a bomb so that the same residence time (application time) as in 1) is achieved.

(3) As a result of the experiment, the initial number of bacteria was 107 cells/ml, and the number of viable bacteria was approximately 105 cells/ml after the treatment in 1).
After the treatment in 2), the number of viable bacteria was approximately 102 cells/
ml.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electric circuit of a high-voltage electric field pulse generator;
Figure 2 is a sectional view of a continuous sterilization tank with a meandering channel;
Figure 4 and Figure 4 are cross-sectional views of a continuous sterilization tank with double cylindrical electrodes, Figure 5 is a cross-sectional view of a quarter-type sterilization tank, and Figure 6 shows the relationship between the number of applied pulses and the number of viable microorganisms. Figure 7 is an exploded perspective view of a batch-type sterilization tank, Figure 8 is an electron micrograph showing the shape of microorganisms fi (beer yeast morphology), and Figure (a) is a pulsed electric field. Figure (b) shows the state before application of the pulsed electric field and after the application of the pulsed electric field. 1...Slidac, 2...High voltage transformer, 3...
・High voltage diode, 4... Charging resistor, 5... Capacitor, 6... Spark gap, 7, 15... Sterilization tank, 8... High voltage probe, 9... Oscilloscope,
10, 21, 26.27... Electrode, 11... Protruding plate part, 12.19... Inner tube electrode, 13.20... Outer tube electrode, 17... O ring, 18...・Ring, 22.
24.28...Transparent acrylic plate, 23.30...Transparent acrylic tube, 25.29...Ground connection.

Claims (1)

[Claims] In a method for sterilizing liquid foods in which a high-voltage electric field pulse is applied with an electric field strength of 2 to 100 kV/cm, a pulse waveform rise time of 20 nsec to 1 μsec, and a pulse waveform width of 100 nsec to 1 msec, the liquid food A method for sterilizing liquid foods, which is characterized by giving the food a stirring action.