JPH0311755B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for sterilizing beverages. More specifically, the present invention relates to a method of sterilizing germs in a beverage liquid by applying pulses of a high voltage electric field. [Prior art] One of the factors that must be kept in mind when manufacturing beverages batchwise or continuously is:
This is to prevent bacterial contamination of beverage liquids, that is, beverage raw materials, semi-finished products, and finished products. Bacterial contamination is also regulated under the Food Sanitation Law. In particular, since it is customary to manufacture beverages by continuous operation for a long period of time, once bacterial contamination occurs, it will have a serious effect on continuous operation. Therefore, various methods for preventing bacterial contamination of beverage liquids have been proposed and developed. Common examples include heat sterilization and filter sterilization. [Problems to be solved by the invention] However, in the sterilization method by heating, the quality of the beverage may change due to heating, so temperature conditions and heating time are limited, making it difficult to carry out satisfactory sterilization. . In addition, the sterilization method using filters has high running costs and problems with longevity due to filter clogging. On the other hand, as an electrical method, it is possible to sterilize by applying a high-voltage electric field (e.g., arc discharge, plasma discharge), but an excessive current flows through the object being discharged, causing electrolysis or chemical changes. Even if the desired bactericidal effect is achieved, the quality of the beverage will change. This invention was made based on the above-mentioned background, and its purpose is to easily and economically prevent bacterial contamination of beverage raw materials, semi-finished products, and finished products, with minimal impact on beverage quality. The goal is to provide a method to do so. [Means for solving the problem] As a result of various research studies conducted by the present inventors to solve this problem, the present inventors found that the application of high-voltage electric field pulses affects microorganisms [Akira Mizuno et al.: Chemistry] Collected Abstracts of the National Conference of the Japan Society of Engineers of Japan (1986), p. 211 and Akira Mizuno et al.: Abstracts of the National Conference of the Institute of Electrical Engineers of Japan (1986), p. 709]. The effect of applying a high-voltage electric field pulse is that a shock wave or electric field is generated by applying a high-voltage electric field pulse in a liquid.
This is thought to be due to physical damage (for example, damage to cell membranes and cell walls) to the microorganisms caused by the generated shock waves or electric fields. Furthermore, as a result of further testing and research, the inventors discovered that applying a high-voltage electric field pulse to a beverage liquid under predetermined conditions is effective in achieving the object of the present invention, leading to the completion of the present invention. That is, the beverage sterilization method of the present invention is characterized in that a beverage liquid is sterilized by applying a high-voltage electric field pulse between electrodes under the following conditions. (a) Use a coaxial double cylindrical electrode consisting of an outer cylinder that constitutes one electrode and an inner cylinder that constitutes the other electrode. (b) Continuously supply drinking liquid between the outer tube electrode and the inner tube electrode. (c) Electric field strength when applying a high-voltage electric field pulse of 2 kV/cm to 100 kV/cm between both electrodes of the outer cylinder and inner cylinder, rise of the pulse waveform of 20 nsec to 1 μsec, and width of the pulse waveform of 100 nsec to 1 msec. So, apply it. In a preferred embodiment of the present invention, a sterilization tank having coaxial double cylindrical electrodes in which each cylinder has a substantially perfect circular cross section is used, and a high voltage electric field pulse is applied between the coaxial double cylindrical electrodes, Beverage liquid can be continuously supplied between the electrodes to perform sterilization. [Operation] When a high-voltage electric field pulse is applied to a beverage liquid that is continuously supplied under the application conditions according to the present invention, as described above, the high-voltage electric field pulse generates shock waves or rapid fluctuations in the electric field in the liquid, and the generated shock waves or Physical damage (for example, damage to cell membranes and cell walls) is selectively applied to microorganisms by changing the electric field. On the other hand, various non-microbial components (proteins, carbohydrates, vitamins, etc.) in the beverage are not substantially affected by the pulsed shock waves or electric field fluctuations. Note that the above explanation is for understanding the present invention, and does not limit the scope of the present invention. This invention will be explained in more detail below. The beverage sterilization method of the present invention is characterized in that a beverage liquid is sterilized by applying a high-voltage electric field pulse between electrodes under the following conditions. (a) Use a coaxial double cylindrical electrode consisting of an outer cylinder that constitutes one electrode and an inner cylinder that constitutes the other electrode. (b) Continuously supply drinking liquid between the outer cylinder electrode and the inner cylinder electrode. (c) A high-voltage electric field pulse is applied between the electrodes of the outer cylinder and the inner cylinder, and the electric field strength when applying a pulse of 2 kV/cm to 100 kV/cm, the rise of the pulse application type of 20 nsec to 1 μsec, and the pulse waveform of 100 nsec to 1 msec. width, to be applied. Sterilization target The sterilization target of the present invention is a beverage liquid from which germs are preferably removed, that is, raw materials for the beverage,
These are semi-finished products and finished products. Examples of such items include soft drinks, alcoholic beverages, soy sauces, lactic acid drinks, milk, liquid dairy products, oils, coffee drinks,
These include liquid seasonings, their raw materials, and manufacturing intermediates. Application of high-voltage electric field pulse/sterilization By applying a high-voltage electric field pulse to the above-mentioned beverage liquid that is continuously supplied, the quality components of the beverage liquid are not altered (e.g., protein denaturation, chemical changes, etc.) kills germs. The application of high-voltage electric field pulses is usually performed by applying a high voltage to an electrode immersed in a beverage liquid using a discharge switch so as to achieve a predetermined electric field strength. In a preferred embodiment of the present invention, a sterilization bath having coaxial double cylindrical electrodes is used, and by applying a high voltage electric field pulse between the coaxial double cylindrical electrodes, the electric field is continuously supplied between both electrodes. It is possible to sterilize beverage liquids. (a) High-voltage electric field pulse The high-voltage electric field pulse used in this invention has a maximum electric field strength of 2 kV/cm between the electrodes when applied.
~100kV/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 approximately 20nsec to 1μsec, and the width is approximately
It is a high-speed pulse (or short-time pulse) of 100nsec to 1msec. This fast pulse is obtained by briefly discharging the capacitor charging energy through a discharge switch. As the discharge switch, a stationary gap, a rotating gap, a thyristor, a thyratron, etc. can be used. Ordinary aqueous solutions contain large amounts of ions and are good electrical conductors, so when a direct current 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. In other words, it is characterized by the ability to create a field with high electric field strength in a conductive aqueous solution [Masayuki Sato et al.: Abstracts of the Gunma Conference 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. (b) Electrode The electrode may be of any type (e.g. platinum, stainless steel,
graphite, etc.), shape (e.g. cylindrical, plate-like,
wire shape, needle shape), size, and immersion position (for example, 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. A preferable electrode in this invention is a coaxial double cylinder type electrode, as shown in FIG. 1, in which each cylinder has a substantially perfect circular cross section. In this embodiment, a wide bubble reservoir (bubble removal) is provided between the electrodes at the top, and the beverage liquid can be continuously supplied between the electrodes to facilitate sterilization. (c) Conditions for applying high-voltage electric field pulses In order to obtain the desired sterilizing effect with the high-voltage electric field pulses specified in (a), various application conditions, such as the number of applied pulses, are set. It is known that the killing characteristics of baker's 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 (1986) p. 211 and Mizuno et al. Akira et al.: Collection of lecture abstracts from the National Conference of the Institute of Electrical Engineers of Japan (1986) p.709].
If the sterilizing effect against each target germ is determined in advance through a preliminary experiment, the application conditions can be determined using an experimental formula, so the various conditions for obtaining the desired sterilizing effect can be determined using that formula. It can be set arbitrarily within the range of . [Effects of the Invention] According to this invention, bacteria in a beverage liquid can be sterilized without impairing the quality of the beverage.
Furthermore, running costs can be reduced in terms of energy, making it economical. By using a sterilizing tank having coaxial double cylindrical electrodes, each of which has a substantially perfect circular cross section, which is a preferred embodiment of the present invention, a drinking liquid can be passed between the coaxial double cylindrical electrodes. It can be continuously supplied and sterilized, effectively preventing bacterial contamination in the treatment process. [Example] Reference Example A preliminary experiment was conducted regarding the relationship between the number of applied pulses and the survival rate of microorganisms when high-voltage electric field pulses were applied. Here, the electrode is of a coaxial double cylindrical type as shown in Fig. 1, and the cross section of each cylinder is substantially a perfect circle (outer cylinder inner dimensions, length 500 mm x inner diameter 60 mm/
It is a sterilization tank with a thickness of 5 mm, inner cylinder outer dimensions, length 400 mm x outer diameter 50 mm x thickness 2.5 mm, electrode distance 5 mm), and the second
Sterilization was carried out using the system shown in the electrical circuit diagram shown in the figure, with an applied electric field strength of 30 kV/cm. The survival rate results are shown in Figure 3. In addition, the sterilization conditions when carrying out the present invention may be set so that the necessary sterilization effect can be obtained based on these results. In this figure, n ₀ = initial number of bacteria (cells/ml), n = number of bacteria after high-speed pulse discharge (cells/ml), n/n ₀ = survival rate, α = number of applied pulses (480 pulses/min) It is. Example 1 Beer in which Lactobacillus brevis (IFO 3345) cells were suspended (number of viable bacteria ^1.9
Ep=20kV/cm, residence time 11 minutes, number of applied pulses
High voltage electric field pulses were applied continuously at 5280 (450 pulses/min). As a result, at the exit of the sterilization tank
Lactobacillus brevis was killed at Ocells/ml, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the beer was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 1 along with the tasting results. As shown in Table 1, no change in quality was observed due to pulse application.

[Table] Example 2 Wort liquid in which Enterobacter aerogenes (IFO13534) cells were suspended (sugar content 11°P, number of viable bacteria 1.2×
10 ² cells/ml) in the same system and sterilization tank as in the reference example, electric field strength Ep = 20 kV/cm, residence time
High-voltage electric field pulses were continuously applied for 11 minutes at a number of applied pulses of 5280 (480 pulses/min). As a result, at the exit of the sterilization tank, Enterobacter aerogenes
ml, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the wort liquid was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 2. As shown in Table 2, no change in quality was observed due to pulse application. In addition, beer was obtained by brewing using the sterilized wort liquid. This beer also had no quality problems.

[Table] Example 3 Red wine with suspended bacteria of Saccharomyces cerevisiae (IFO 0259) (number of viable bacteria 5.1×10 ³ cells/
ml) in the same system and sterilization tank as in the reference example, electric field strength Ep = 15 kV/cm, residence time 18.7 minutes,
High-voltage electric field pulses were continuously applied with a number of applied pulses of 8976 (480 pulses/min). As a result, Saccharomyces cerevisiae died at a rate of Ocells/ml at the exit of the sterilization tank, and this sterilization effect could be stably maintained during continuous sterilization. The quality of red wine was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 3 along with the tasting results. As shown in Table 3, no change in quality was observed due to pulse application.

[Table] Example 4 Grape juice in which Saccharomyces diastaticus (IFO 1046) cells were suspended (sugar content 23%, number of viable bacteria
4.5×10 ³ cells/ml) in the same system and sterilization tank as the reference example, electric field strength Ep = 15 kV/cm, residence time 18.7 minutes, number of applied pulses 8976 (480 pulses/min).
A high-voltage electric field pulse was continuously applied. As a result, Saccharomyces diastaticus at the outlet of the sterilization tank
Ocells/ml were killed, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the grape juice liquid was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 4. As shown in Table 4, no change in quality was observed due to pulse application. In addition, wine was obtained by brewing using grape juice after sterilization. This beer also had no quality problems.

[Table] Example 5 Sake in which Lactobacillus homohiochi (H-42, provided by the Department of Fermentation, Department of Agricultural Chemistry, Faculty of Agriculture, University of Tokyo) was suspended (number of positive bacteria: 2.9 x 10 ⁴ cells/ml),
Same as the reference example, the system and sterilization tank were set at electric field strength Ep = 50 kV/cm, residence time 5.2 minutes, and number of applied pulses.
High voltage electric field pulses were applied continuously at 2496 (480 pulses/min). As a result, at the exit of the sterilization tank
Lactobacillus homohiochi was killed at Ocells/ml, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the sake was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 5 along with the tasting results. As shown in Table 5, no change in quality was observed due to pulse application.

[Table] Example 6 A carbonated drink in which Bacillus megaterium (IFO 3003) cells were suspended (number of viable bacteria: 2.1×10 ³ cells/ml),
Similar to the reference example, the system and sterilization tank were set to electric field strength Ep = 30 kV/cm, residence time 9.4 minutes, and number of applied pulses.
High voltage electric field pulses were applied continuously at 4498 (480 pulses/min). As a result, Bacillus at the outlet of the sterilization tank
megaterium died at Ocells/ml, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the carbonated beverages was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 6 along with the tasting results. As shown in Table 6, no change in quality was observed due to pulse application.

[Table] Example 7 Fruit juice drink containing suspended cells of Enterobacter aerogenes (IFO 13534) (mandarin orange juice 70%, number of viable bacteria 1.2)
x 10 ² cells/ml) in the same system and sterilization tank as in the reference example, electric field strength Ep = 10 kV/cm, residence time 22.0 minutes, number of applied pulses 10560 (480 pulses/min).
A high-voltage electric field pulse was continuously applied. As a result, Enterobacter aerogenes at the exit of the sterilization tank
Ocells/ml, and this bactericidal effect could be stably maintained during continuous sterilization. The quality of the fruit juice beverages was tested before and after sterilization by high-voltage electric field pulses, and the results are shown in Table 7 along with the tasting results. As shown in Table 7, no change in quality was observed due to pulse application.

【table】 [Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the sterilization tank used in the example.
FIG. 2 is a schematic diagram of the electric circuit of the device used in the examples, and FIG. 3 is a diagram showing the relationship between the number of applied pulses and the survival rate of microorganisms. R ₁ , R ₂ , R ₃ ... High voltage resistor, C ₁ , C _p ... Capacitor (Cp is for discharge control), 1 ... Slider, 2 ... High voltage transformer, 3 ... High voltage rectifier, 4 ...Copper plate, 5...Spark gap, 6...
...Sterilization tank (capacity 300ml), 7...Ground wire, 11...
...Outer tube electrode, 12...Inner tube electrode, 13...Sterilization tank, 14...O ring.

Claims (1)

[Claims] 1. A method for sterilizing a beverage liquid, which comprises sterilizing the beverage liquid by applying a high-voltage electric field pulse between electrodes under the following conditions. (a) Use a coaxial double cylindrical electrode consisting of an outer cylinder that constitutes one electrode and an inner cylinder that constitutes the other electrode. (b) Continuously supply drinking liquid between the outer cylinder electrode and the inner cylinder electrode. (c) Electric field strength when applying a high-voltage electric field pulse of 2 kV/cm to 100 kV/cm between both electrodes of the outer cylinder and inner cylinder, rise of the pulse waveform of 20 nsec to 1 μsec, and width of the pulse waveform of 100 nsec to 1 msec. So, apply it. 2. The cross section of each cylinder of the electrode is substantially a perfect circle;
A sterilization method according to claim 1.