JPH0628566B2 - Liquid Food Sterilization Method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION <Industrial field of application> The present invention relates to a method for sterilizing liquid foods (foods at the product stage, and liquids including these raw materials and semi-finished products). Regarding More specifically, the present invention relates to a method of sterilizing sterilization in liquid food products by applying high piezoelectric field pulses.

<Prior Art> One of the most important points to be noted when manufacturing a liquid food is to prevent contamination by various bacteria.
As a method for preventing contamination of liquid foods, that is, liquid foods containing these raw materials, semi-finished products and products, with bacteria, there are generally a heat sterilization method and a filter sterilization method.

However, in order to obtain a satisfactory sterilizing effect by the heat sterilization method, the heat deteriorates the quality of the liquid food product. Further, the sterilization method using a filter has a problem of life due to clogging of the filter.

Therefore, in order to use energy efficiently for sterilization, a sterilization method by igniting a direct current voltage or an alternating current voltage on a liquid food has been considered, but in both cases, sterilization is performed by a product of an electrode reaction. Since it is based on the basic principle, it is difficult to apply it to food.

Further, the sterilization method using a pulsed discharge shock wave in water, energy efficiency is good, mechanical strength of the food container used during sterilization, the size of the noise, the liquid to be sterilized by the metal eluted from the electrode, ie, There are drawbacks such as contamination of liquid foods.

On the other hand, the sterilization method by applying a pulsed electric field is described in Japanese Patent Application No. 62-154825 (“Sterilization method of immobilized biocatalyst environment”) and Japanese Patent Application No. 62-252531 (“Beverage sterilization method” by the present applicant. )) As described in the specification,
Although it has the advantages that it can selectively sterilize only the bacteria around the immobilized biocatalyst and that it does not affect the flavor of the beverage at all, a drastic reduction in the viable cell count could not be expected.

Furthermore, the method of Sakurauchi et al. (Yujiro Sakurauchi, Eiaki Kondo: “On the bactericidal effect of high-voltage fields against microorganisms”, Journal of the Japanese Society of Agricultural Chemistry, Vol.54, No.10, pp.837-844, 1980), and Sale Etc. (AJH Sale and WA Hamilton., Ef
fects of high electric fields on microorganisms.,
Biochim. Biophys. Acta. 148, pp.781-800 1967) also uses a very large-capacity capacitor to supply a large amount of power, which poses a problem in industrial commercialization and is not sufficient in terms of sterilization effect.

[Outline of Invention]

<Summary> The present invention aims to provide a solution to the above points and to provide a method capable of significantly reducing the number of viable bacteria in a liquid food even by a low-power pulsed electric field. The object of the present invention is to achieve this object by imparting a stirring action that causes a change in flow due to turbulence to the liquid food as described above.

That is, in the liquid food sterilization method 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 pulse waveform width is 10.
In a method of sterilizing a liquid food by applying a high piezoelectric field pulse of 0 nsec to 1 msec, the liquid food is provided with a stirring action for causing a change in flow due to a turbulent flow.

<Operation> When a high-piezoelectric field pulse is applied to the liquid food under the application conditions according to the present invention as described above, and a stirring action is applied to the liquid food before or after the pulse application or during the pulse application, the electric field fluctuation due to the pulse is generated. , And the generation of turbulent flow due to the stirring action (generation of flow change), selectively cause greater damage (eg, cell membrane or cell wall damage) to microorganisms in the liquid food. On the other hand, this pulsing and stirring action does not substantially affect the various non-microbial components (proteins, carbohydrates, vitamins, etc.) in the liquid food.

<Effect> According to the sterilization method of the present invention, the synergistic effect of the application of the high-piezoelectric field pulse and the stirring action that causes a change in the flow due to turbulent flow can be achieved with a small amount of power without degrading the quality of the liquid food. Miscellaneous bacteria in food can be sterilized.

[Specific Description of the Invention]

In the liquid food sterilization method according to the present invention, the electric field strength upon pulse application is 2 to 100 kV / cm, the rise time of the pulse waveform is 20 nsec to 1 μsec, and the pulse waveform width is 100 nsec to 1.
In the sterilization method of a liquid food applying a high piezoelectric field pulse of msec, the liquid food is provided with a stirring action to generate a change in flow due to turbulence, which is characterized in the above. .

Further, the sterilization method according to the present invention can be applied to sterilization of liquid food, liquid medium for culturing microorganisms, animal and plant cells, liquid pharmaceuticals, etc. or tap water and sewage.

<Liquid Food> The liquid food as used in the present invention is a raw material, a semi-finished product, or a product of a liquid or fluid or semi-fluid food. Examples thereof include liquors such as beer or wine, soft drinks, mayonnaise, tomato puree, retort foods, soy sauce, lactic acid drinks, milk, liquid dairy products, oils, coffee drinks, liquid seasonings. Etc., and these raw materials, manufacturing intermediates, etc.

<Sterilization by applying high-piezoelectric field pulse and imparting stirring action> Stirring that applies a high-piezoelectric field pulse to the above-mentioned liquid food and causes a change in flow due to turbulence in the liquid food before or after pulse application or during pulse application By exerting the action, the germs in the liquid food can be more surely killed without degrading the quality component of the liquid food (eg, denaturation of protein, chemical change, etc.).

(1) Application of high-piezoelectric field pulse The high-piezoelectric field pulse is usually applied by applying a high voltage to an electrode immersed in a liquid food by using a discharge switch so that a predetermined electric field strength is obtained. .

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

Further, for example, if a substantially cylindrical box type sterilization tank having electrodes on opposite side walls as shown in FIG. 5 is used, it becomes a batch sterilization method for liquid foods.

(A) High-piezoelectric field pulse The high-piezoelectric field pulse used in the present invention has a maximum electric field strength of 2 kV / cm to 100 kV / cm between electrodes when applied, and a pulse waveform when the voltage between the electrodes at that time is monitored by an oscilloscope. It is a high-speed pulse (or short-time pulse) having a very fast rise of about 20 nsec to 1 μsec and a width of about 100 nsec to 1 msec in (a waveform showing a temporal change of voltage). This high-speed pulse is
It is obtained by discharging charging energy in a short time through a discharge switch. A static gap, a rotating gap, a thyristor, a thyratron, or the like can be used as the discharge switch. Since an ordinary aqueous solution contains a large amount of ions, it is an electrically good conductor. Therefore, when a DC voltage is applied to the immersed electrode, a large current flows and electrolysis occurs. However, when applying the above pulse,
Although electrons run at high speed, the movement of ions to carry an electric current is slow, so that an aqueous solution exhibits properties similar to those of an electrically insulating liquid. That is, it is characterized in that a field having a high electric field strength can be created in an electrically conductive aqueous solution [Masayuki Sato et al .: The Chemical Engineering Society Gunma Conference Lecture Collection (1986) p. 213]. It should be noted that the polarities of the high piezoelectric field pulse are positive and negative, but both can be used in the present invention.

(B) Electrode If the electrode can be applied with the target high-piezoelectric field pulse, the type (eg platinum, stainless steel, graphite, etc.), shape (eg cylindrical, plate-shaped, wire-shaped, needle-shaped), size The immersion position (for example, the distance between electrodes) is not limited. However, since sterilization is actually performed only in the portion to which the high piezoelectric field pulse is applied between the electrodes, it is necessary to select these various conditions so that the desired sterilization effect can be obtained.

(C) High-piezoelectric field pulse application conditions In order to obtain the desired sterilization effect by applying the high-piezoelectric field pulse specified in (a) and applying the stirring action described later, various application conditions, such as the number of applied pulses, are set. Set. It is known that the killing characteristics of baker's yeast by applying a high-piezoelectric field pulse are approximated to a Weidel distribution [Akira Mizuno et al .: The Chemical Engineering Society of Gunma Conference, Abstracts (1986) p. 211 and Akira Mizuno et al .: Proceedings of the Annual Conference of the Institute of Electrical Engineers of Japan (1986) p. 709]. According to this, applying conditions, if the bactericidal effect on each target bacteria is obtained in advance in a preliminary experiment, the result is derived by an empirical formula, so the various conditions for obtaining the desired bactericidal effect are given in the formula. It can be arbitrarily set within the range.

One preferable example of the high-piezoelectric field pulse generating device as described above is shown in FIG. 1 as a schematic diagram (electric circuit schematic diagram).

In this device, an AC 100V power source (50 Hz) is regulated by a sliderac 1, 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 when the spark gap 6 is electrically connected, and a high piezoelectric field pulse is applied in the sterilization tank 7. Observation of the pulse waveform can be performed by the oscilloscope 9 through the high voltage probe 8.

(2) Application of agitation action As described above, the time at which the agitation action that causes a change in the flow due to turbulence is applied to the liquid food is before, after, or during the application of the high-voltage pulse. Alternatively, a plurality of periods can be combined as needed. The application of the high-piezoelectric field pulse and the operation of the stirring action may be performed at the same time, or both may be performed alternately.

As a method of giving a stirring action, any purposeful method can be used, and the following methods are representative examples.

(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 stirring rod (eg, glass rod), or perform suction and discharge operations using a pipette.

(C) Using a sterilization tank having a reciprocatingly bent flow path, a change in flow (turbulent flow or the like) is generated in the liquid food at the bent part of the flow path (see FIG. 2).

(D) Providing a protruding plate portion that is inclined in the flow direction in the flow path to cause a change in the flow of the liquid (for example, the protruding plate portion 11 is provided in the linear flow path portion of the sterilization tank shown in FIG. 2). Can be).

(E) A narrow portion and a wide portion are provided in the flow passage to change the width of the flow passage, whereby the liquid is hydrodynamically stirred to change the flow of the liquid (for example, FIG. 4). As shown in (4), spiral or ring-shaped irregularities arranged at appropriate intervals can be provided on the outer peripheral surface of the inner cylindrical electrode of the sterilization tank having the coaxial double cylindrical electrode).

(F) By supplying the liquid food at a high flow rate to the coaxial double cylinder type continuous sterilization tank as shown in FIG. 3, the flow of the food liquid is changed.

Using a combination of the high piezoelectric field pulse and stirring action as described above, regarding the pulse application condition and the stirring condition, the sterilizing effect on each target bacteria is obtained in advance in a preliminary experiment, and the result is derived by an empirical formula. Various conditions for obtaining a desired bactericidal effect can be arbitrarily set within the range of the formula.

Although the pulse can be applied with a smaller electric power when the distance between the electrodes is made smaller, the present invention which gives a stirring action can obtain a larger sterilizing effect even by the small electric power pulse electric field. Beer yeast damaged by pulsed electric field (S.ce
The morphology of revisiae) is shown in FIG.

<Experimental example> Example 1: An experiment was conducted on the relationship between the number of applied pulses and the presence / absence of the stirring action when the high-piezoelectric field pulse was applied, and the survival number of microorganisms. Here, as shown in FIG. 5, sterilization was performed in a substantially cylindrical box type sterilization tank by the system of the electric circuit schematic diagram shown in FIG. In FIG. 5, reference numeral 21 is both electrodes, 22 and 24 are transparent acrylic plates, 23 is a transparent acrylic tube, 25 is a portion connected to the ground, and 30 is an injection port made of a transparent acrylic tube.

(1) Various conditions Sterilization tank: Internal capacity 15 ml (Fig. 5) Electrode Two circular parallel electrodes (made of stainless steel) Sample: Beer Sterilized bacteria: S. cerevisiae IFO 0259 Initial number of bacteria: Approximately 10 ⁷ cells / ml electric field Strength: 20 kV / cm Capacitor capacity: 0.004 μF Pulse period: 20 msec (2) Experimental method Every time a high piezoelectric field pulse is applied 1200 times (each 24 seconds), the sample in the sterilization tank is agitated with a pipette (suction and discharge). The operation) was performed three times (near both electrodes and in the center) to determine the relationship between the pulse application number and the viable cell number.

(3) Experimental Results As shown in FIG. 6, in the pulse application method without stirring,
The viable cell count of at most about 10 ⁴ cells / ml was reduced to a viable cell count of 10 ¹ cells / ml by the stirring method.

Example 2: Sterilization is carried out by the system of the electric circuit schematic diagram shown in FIG. 1 using a substantially box-shaped sterilization bath as shown in FIG. 2 in the figure
6 and 27 are both electrodes, 28 is a transparent acrylic plate, 29
Is a part connected to the ground.

(1) Various conditions Sterilization tank: Horizontal type (Fig. 7) Sample liquid: Distilled water Bacteria to be sterilized: Yeast (S. cerevisiae) Initial number of bacteria: Approx. 10 ⁷ cells / ml Electric field strength: 30 kV / cm Capacitor capacity: 0 0.004 μF Pulse period: 20 ms (2) Experimental method After applying the high-piezoelectric field pulse 1200 times (about 24 seconds), the sample liquid was taken out from the sterilization tank, and the operation of applying the injected pulse again was repeated 4 times.

(3) Experimental results When the initial number of bacteria is 10 ⁷ cells / ml, about 4 × 1 after the experiment
A large decrease in the number of viable bacteria is seen with 0 ² cells / ml.

Example 3: Using the continuous sterilization tank shown in FIG. 2, sterilization is performed by the system of the electric circuit schematic diagram shown in FIG. In the figure, 10 is both electrodes, and 11 is a protruding plate portion.

(1) Various conditions Sterilization tank: Continuous sterilization tank shown in Fig. 2, capacity of one tank 60 ml Sample liquid: distilled water Bacteria to be sterilized: Enterobacter aerogenes Initial number of bacteria: about 10 ⁵ cells / ml Electric field strength: 30 kV / cm Capacitor capacity: 0.012 μF Pulse period: 100 ms (2) Experimental method 1) Fill the sterilization container with the sample liquid and apply the pulse 4800 times, and then take out the sample.

2) Repeating four times by moving the pump to move about 60 ml of the sample liquid every time the pulse is applied 1200 times, 1)
The sample is taken out so that the residence time is the same as in.

(3) Experimental results When the initial number of bacteria is 10 ⁵ cells / ml, the result of 1) is about 5 ×
It is 10 ³ cells / ml, whereas in 2) it is 5 × 10 ¹ ce.
lls / ml, a large decrease in viable cell count is seen.

Example 4: Using the continuous sterilization tank shown in FIG. 4, sterilization is performed by the system of the electric circuit schematic diagram shown in FIG. In the figure, 19 is an inner cylinder electrode and 20 is an outer cylinder electrode.

(1) Various conditions Sterilization tank: as shown in Fig. 4, cylindrical shape with a capacity of 500 ml,
Interval between electrodes 3-5mm Sample liquid: Beer Sterilizing bacteria: S. cerevisiae Initial bacterial count: Approx. 10 ⁷ cells / ml Electric field strength: 40kV / cm Capacitor capacity: 0.05μF Pulse period: 50ms (2) Experimental method 1 ) Fill the sterilization tank with the sample liquid and apply the pulse 7200 times, and then take the sample.

2) Collect a sample while continuously injecting and discharging the sample liquid at 83 ml / min by a pump so that the retention time (application time) is the same as that in 1).

(3) Experimental results When the initial number of bacteria is 10 ⁷ cells / ml, the treatment of 1) gives about 10 ⁵
Although the viable cell count is cells / ml, the viable cell count decreases to about 10 ² cells / ml after the treatment of 2).

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electric circuit of a high piezoelectric field pulse generator,
FIG. 2 is a sectional view of a continuous sterilization tank having a bent flow path,
Figures and 4 are cross-sectional views of a continuous sterilization tank with double cylindrical electrodes, Fig. 5 is a cross-sectional view of a batch-type sterilization tank, and Fig. 6 is the relationship between the number of applied pulses and the number of viable microorganisms. FIG. 7 is an exploded perspective view of a batch-type sterilization tank, FIG. 8 is an electron micrograph showing the form of microorganisms (form of beer yeast), and FIG. , (B) shows the state after application of the pulsed electric field. 1 ... Slidar, 2 ... High voltage transformer, 3 ... High voltage diode, 4 ... Charging resistance, 5 ... Capacitor, 6 ...
… Spark gap, 7,15 …… Sterilizer, 8 …… High-voltage probe, 9 …… Oscilloscope, 10,21,26
27 ... Electrode, 11 ... Projection plate part, 12, 19 ... Inner cylinder electrode, 13, 20 ... Outer cylinder electrode, 17 ... O-ring, 1
8 ... Ring, 22, 24, 28 ... Transparent acrylic plate,
23,30 ... Transparent acrylic tube, 25,29 ... Ground connection.

Claims (1)

[Claims] 1. The electric field strength when a pulse is applied is 2 to 100 kV /
cm, rise time of pulse waveform is 20 nsec to 1 μsec,
In a sterilization method of a liquid food applying a high piezoelectric field pulse having a pulse waveform width of 100 nsec to 1 msec, the liquid food is provided with a stirring action for causing a change in flow due to turbulent flow. How to sterilize food.