JP4359680B2 - Fruit juice sterilization method - Google Patents

Description

  The present invention relates to a method for sterilizing fruit juice using both pressurization and heating in a fruit juice production process, and particularly sterilizes microorganisms of yeast fungi, which are the main cause of quality deterioration of citrus citrus fruit juice such as sudachi, by a simple method. Thus, the present invention relates to a fruit juice sterilization method for preventing deterioration of quality associated with the action of yeasts without impairing the unique refreshing flavor and flavor.

  Sudachi, which is famous as a special fruit of Tokushima Prefecture, is called perfume citrus, and has a unique scent and color. It's being used. Other fragrant citrus fruits such as kabosu, lemon and yuzu are widely used for food as much as Sudachi. These fruit juices are generally concentrated in the fruit harvest season and stored so that they can be shipped throughout the year. Therefore, stably maintaining the quality peculiar to citrus citrus juice is an important issue in the field of agricultural products in order to secure commercial value.

  In general, in the manufacturing process of fruit juices, juice is often squeezed without peeling off in order to make use of the skin of fruits as raw materials and the aromatic components and components contained in the fruits. However, naturally occurring fungi such as yeast exist inside and outside the skin of fruits, and they are mixed in the juice after squeezing and fermented in the juice to cause browning and quality deterioration. In order to maintain quality, it is necessary to prevent fermentation by yeast. In view of this point, various sterilization methods have been conventionally devised. For example, a method using filtration and additives (see Patent Document 1), a method using high-pressure sterilization and addition of fruit extract components (see Patent Document 2), a method of pressure treatment in a temperature range of 15 ° C. or lower (see Patent Document 3), 60 There are proposals such as a method of performing sterilization and enzyme deactivation by ultra-high pressure of 100 MPa or more at a temperature of ℃ or lower (see Patent Document 4), a method by accelerated electron beam irradiation (see Patent Document 5), and the like.

  In general, the heat treatment is performed at a temperature of 65 ° C. or more, usually around 90 ° C. However, citrus citrus fruit juices, whose fragrance and color are important features, have problems such as loss of fragrance due to heating, browning and generation of heated odor. Moreover, in addition processing, such as a chemical | medical agent, while sterilizing, there exists a problem of impairing the fragrance and flavor peculiar to citrus citrus. In addition, a large amount of heat is required, and there is a problem in terms of energy saving.

  Pressure treatment has attracted attention as an alternative to such heat treatment, and research on food processing using high pressure at room temperature has been actively studied. In 1914, Hite et al. Reported the effect of pressure treatment on the preservation of fruit juices (see Non-Patent Document 1), and in Japan since around 1990, Hayashi et al. Collection has been promoted, and pressurized foods have been put to practical use with jam or the like (see Non-Patent Document 2). In order to investigate the effect of pressure on Escherichia coli, Gram-negative or positive bacteria, and yeasts, the inventors have also applied ultra-high pressure to microorganisms, changing cell membrane hydrophobicity, cell elongation, and changes in the number of viable bacteria. I have observed such phenomena. As a result, it was confirmed that the pressure treatment had an effect of sterilizing microorganisms in the food.

Moreover, about the effect of the pressurization process with respect to the fungi in citrus juice, Kobayashi et al.
MPa has been reported to die after 10 minutes of treatment. For Sudachi fruit juice, Hayashi et al. Reported that yeast was killed by treatment at 400 MPa for 2 minutes (see Non-Patent Document 3), and the present inventor and Inai et al. Performed treatment at 400 MPa for 10 minutes. Thus, it was confirmed that yeast and mold could be completely sterilized, and deterioration of quality such as aroma components could be suppressed even after storage at −20 ° C. for 120 days (see Non-Patent Document 4).
JP-A-5-137546 JP-A-5-146280 JP-A-5-328950 JP-A-6-217743 Japanese Patent Laid-Open No. 2001-8684 Hite, BH, Giddings, NJ and Weakley, CE, The effect of pressure on certain microorganismsencountered in the preservation of fruits and vegetables, Bulletin 146, WestVirginia University Agricultural Experiment Station, 3-67 (1914) "High-pressure use for food" Hayashi Rikimaru (Sanei Publishing), pages 1-30 (1989) Tokushima Food Processing Laboratory Report, Vol. 37, pages 22-30 (1989) Iuchi, A., Hayashi, K., Tamura, K., Kono, T., Miyashita, M. and Chakraborty, SK, Technique of quality control for Sudachi (Citrussudachi Hort.ex Shirai) juice by high pressure treatment, High Pressure Biosience and Biotechnology, 387-390 (1996)

  However, since the pressure treatment that has been reported in the past uses a high pressure of about 100 MPa to 400 MPa (hereinafter referred to as “ultra-high pressure”), it requires specific equipment and technology in the ultra-high pressure region, and there is a problem with containers filled with fruit juice. However, there have been problems in mass production and quality such as a problem in processing capacity and a residual pressure odor, and it has not been industrially accepted as a method for sterilizing citrus citrus juice.

  In view of the above-mentioned problems in the conventional sterilization method by pressure treatment, the present inventors do not need additives, high temperatures, and ultra-high pressure, and aim to develop technologies that can be processed with simple technology and equipment.・ Survey was conducted. According to this, it has been found that by directly pressurizing the yeast suspension with a certain gas, the yeast has an action of delaying growth, bacteriostasis, and further sterilization. For example, carbon dioxide reacts with water to produce carbonic acid, lowering the intracellular pH, and lethal effects on microorganisms. In the case of fruit juice whose pH is not low, the bactericidal effect due to the pH lowering effect of carbon dioxide can be considered. However, it is not preferable to reduce the pH due to carbonic acid for yeast originally inhabiting fruit juice having a low pH such as sudachi fruit juice, and the texture changes due to the generation of carbonic acid. Nitrogen can also be used as an inert gas, but according to our research, no particular bactericidal effect has been confirmed. Therefore, especially in the manufacturing process of citrus citrus juice, technology that can effectively sterilize the yeast in the juice without using high temperature / ultra-high pressure, that is, inactivate the yeast in the juice and quality such as unique fragrance and color It is necessary to develop a gas suitable for sterilization of fruit juice and to improve the pressure treatment method in order to maintain the odor and prevent the deterioration of quality associated with yeast fermentation.

  Therefore, the problem to be solved by the present invention is a fruit juice sterilization method using both pressurization and heating, particularly without sacrificing the unique scent and flavor of citrus citrus fruit juice represented by sudachi fruit juice. An object of the present invention is to provide a simple and efficient fruit juice sterilization method that prevents deterioration of quality associated with fermentation and does not require high temperature and ultrahigh pressure.

  As a means for solving the above problems, the present inventors pay attention to the gas used for pressure treatment, its pressure, and the temperature for heat treatment, and can be sterilized without using a high temperature or ultrahigh pressure as in the past. As a result of diligent research to develop the technology, we found that it is effective to press the fruit juice in direct contact with oxygen, and by combining this with heat treatment at a relatively low temperature, it is peculiar to citrus citrus fruit juice. The inventors have found a method that can be effectively sterilized while maintaining the scent and color, and have completed the present invention.

That is, the first invention for solving the above problems is a method for sterilizing fruit juice used in combination heating and pressurizing, 60 ° C. which pressure treatment by direct contact with the oxygen gas juice temperature below The fruit juice sterilization method is characterized in that the pressure of the pressure treatment is 5 MPa or more and 10 MPa or less . In the present invention, “pressing the fruit juice in direct contact with oxygen gas” means pressing the fruit juice in direct contact with oxygen, and the fruit juice is usually used. Is not stored in a container such as a flexible bag and indirectly pressurized. Therefore, as a method of pressurization, high-pressure oxygen gas may be press-fitted into a container containing fruit juice, or pressurization may be performed using a piston in a state where oxygen gas and fruit juice coexist in the container. In any case, according to the present invention, in the fruit juice production process, it is possible to perform pressure treatment using oxygen that has not been conventionally used as a gas for pressure treatment of foods, and it is possible to perform relatively low temperature and short time. Thus, it is possible to provide a fruit juice sterilization method that is efficient, energy-saving, and suitable for mass production. In order to sterilize fruit juice, it is not preferable in terms of quality to apply high temperature and high pressure for a long time. According to the present invention, the heat treatment and the pressure treatment with oxygen exhibit a synergistic effect and exert a bactericidal action. Therefore, the pressure for the pressure treatment is 5 MPa or more and 10 MPa or less and does not require an ultrahigh pressure, and the heating temperature is The objective can be achieved at a relatively low temperature of 60 ° C. or lower.

In addition, even if the pressure is 5 MPa or less with respect to the pressure range of the pressure treatment described above , there is a bactericidal effect depending on the combination with heating conditions, but an extremely long time is required. In addition, the sterilizing effect is obtained even at 10 MPa or more, but the high-pressure gas is burdensome in terms of equipment and technology, and is economically disadvantageous. According to the present invention, pressurizing treatment that does not require ultra-high pressure is industrially possible.

2nd invention is the method of 1st invention, The temperature of fruit juice is 40 degreeC or more and 50 degrees C or less The method of disinfection of fruit juice. That is, in the said temperature range, by pressurizing in a short time of about 1 minute at a pressure of 5 MPa or more and 10 MPa or less, it can be sterilized without deteriorating the quality of fruit juice, and the quality deterioration accompanying fermentation of yeast fungi To prevent. On the other hand, although there is a sterilizing effect even at a temperature of 40 ° C. or lower or 50 ° C. or higher, the former requires a long time, and the latter reduces the energy saving effect.

A third invention is a method for sterilizing fruit juice according to any one of the first or second invention, wherein the fruit juice is perfume citrus fruit juice. Examples of perfume citrus include sudachi, kabos, lemon, yuzu, hebes, and seeker. Each of them has a refreshing scent and color, has a strong acidity, and usually exhibits a pH value between 2.4 and 3.0. According to the present invention, it is sterilized without impairing the peculiar refreshing flavor and color of citrus citrus, and quality deterioration accompanying fermentation of yeasts is prevented.

The fourth invention is a method for sterilizing fruit juice in which the citrus citrus fruit is sudachi in the third invention, and is particularly suitable for sterilization of sudachi fruit juice, wherein the heated fruit juice is directly treated with oxygen gas and pressurized. Is a method for sterilizing fruit juice. Sudachi juice has a low pH value of about 2.4 to 2.5. The present inventors have confirmed the presence of strong yeast in a low pH range in sudachi juice (described later), and can effectively sterilize this by combining heat treatment and pressure treatment. Provided is a method for preventing the quality deterioration of sudachi fruit juice associated with.

  Although oxygen has been known to be toxic to microorganisms, the use of oxygen for sterilization by pressurizing fruit juice has never been known and has never been performed. According to the present invention, fruit juice can be sterilized by a pressure treatment at a relatively low temperature and a pressure of about 1/40 that of a conventionally known ultra-high pressure sterilization treatment.

  That is, the method of the present invention in which fruit juice and oxygen are subjected to pressure treatment in direct contact with temperature has less effect on quality and energy saving effect than conventional heat treatment at 65 ° C. or higher, usually around 90 ° C. In addition, the pressure can be processed at an extremely low pressure compared to the conventional ultra-high pressure, so it is simpler in terms of equipment and technology than the ultra-high-pressure sterilization process that requires a special device. It is possible to perform treatment at once or continuously in a short time, and there is an effect that it is possible to provide a sterilization method that is extremely useful for the field of agricultural product processing.

  An embodiment for carrying out the present invention will be described. The harvested fruit is squeezed after washing the surface with a conventional method by washing with water, etc., and the fruit juice from which solid matter has been removed with a sieve or the like is kept at 60 ° C. or lower, preferably 40 ° C. to 50 ° C. in a high-pressure vessel. However, oxygen is directly pressurized with oxygen gas having a pressure of 5 MPa to 10 MPa. In addition, during pressurization, by adding a stirring / mixing action to the fruit juice, the concentration of dissolved oxygen in the fruit juice can be increased and the effect of oxygen can be exhibited efficiently. For the stirring, effects such as a propeller stirrer, rotation or swinging of the container itself, an in-line mixer, and bubbling can be used.

  The time during which the temperature and pressure are maintained in the container, that is, the sterilization time is adjusted according to the temperature and pressure setting conditions and the state of the fruit juice. Preferably, in the case of sudachi fruit juice having a pH of about 2.5, 50 ° C. and 5 MPa Or about 10 minutes under conditions of 40 MPa and 10 MPa, or about 10 minutes under conditions of 40 ° C. and 5 MPa.

  As mentioned above, fruit juice is sterilized by the synergistic effect of heat treatment and pressure treatment with oxygen, but after sterilization treatment, the juice is quickly reduced in pressure and degassed to remove oxygen and replaced with inert gas. Eliminate the effects of oxygen on The temperature is appropriately cooled through a heat exchanger when the fruit juice is discharged from the container, and sent to a subsequent process in fruit juice production. Although an experiment example and an Example demonstrate below, this invention is not limited to these experiment examples and an Example.

(Experimental example)
1. Implementation Method (1) Test Bacteria As a test bacterium, a yeast Candida bodiniii (hereinafter referred to as “bacteria A”) that is strong in a low pH value region was used.

(2) Preparation of test solution for fungus A Yeast that survived in Sudachi juice was isolated and confirmed by the following method. Fruit juice (pH 2.4) obtained by squeezing sudachi was collected, placed in an Erlenmeyer flask, and cultured with shaking in a thermostatic bath at 30 ° C. for 48 hours. 0.1 ml of the fruit juice is smeared on an agar medium and allowed to stand at 30 ° C., and then the colonies formed are scraped of what appears to be yeast and shaken at 30 ° C. until suspended in a YPD medium. Cultured. The bacterial suspension was smeared on a slant medium and allowed to grow, and then stored in a refrigerator. Thus, the yeast isolate | separated from sudachi fruit juice identified the genus species in the foundation and the Japan food analysis center. As a result, the yeast can be separated from the surface of fruits such as soil, olives, and grapes, and has been identified as Candida bodiniii (bacteria A), which has strong viability in a particularly low pH region.

The test solution used was inoculated Bacteria A in a YPD medium, cultured at 30 ° C. for 48 hours with shaking until the stationary phase of growth, and then diluted 25 times with Sudachi juice. From preliminary experiments, the number of bacteria in the test solution was approximately 9 × 10 ⁶ cells / ml. The sudachi juice was stored frozen in advance and thawed before use.

(3) Pressurizing apparatus An outline of the pressing apparatus is shown in FIG. The pressurizing device comprises a high pressure gas cylinder 1 for oxygen, a high pressure gas cylinder 2 for nitrogen, a pressure regulating valve 3, a pressure gauge 4, a pressure display unit 5, a branch valve 6, a pressure relief valve 7, a shutoff valve 8 and a high pressure vessel 9, respectively. As for the piping connecting, a stainless steel pipe having an outer diameter of 1/16 inch was used so that it could withstand high pressure. The pipes connecting the high pressure gas cylinders 1 and 2 and the high pressure vessel 9 were branched from the middle and connected to the pressure gauge 4 and the pressure relief valve 7 respectively. The high-pressure vessel 9 was made of a stainless steel vessel (capacity: about 17 ml) and a lid, and an O-ring was tightened with the lid to prevent pressure leakage. Further, in order to allow simultaneous pressure experiments under different conditions, the pipe was branched into five pipes from the middle and connected to the high-pressure vessel 9 through the shutoff valve 8. The high-pressure gas cylinders 1 and 2 are connected to the branch valve 6 through oxygen and nitrogen pipes, respectively, so that the gas to be used can be selected by opening and closing the valve.

(4) Pressurization of test solution, high-pressure vessel 9 containing the test solution for reduced pressure was sterilized with a dry heat sterilizer at 132 ° C. for 3 hours. When connecting the high-pressure vessel 9 to the pressurizing device, 5.0 ml of the test solution was put in the high-pressure vessel 9 in the clean bench, the lid was closed, and then connected to the piping of the pressurizing device. During pressurization, the pressure regulating valve 3 was gradually opened and pressurized to a predetermined pressure in about 30 seconds. The decompression was carried out for about 30 seconds, the same as the pressurization, and the degassing was slowly performed and the pressure was slowly reduced. After the pressure became normal, the high-pressure vessel 9 was removed. In order to keep the temperature constant during pressurization, the high-pressure vessel 9 was placed in a thermostatic bath. Moreover, in order to heat the test solution to a predetermined temperature, the high-pressure vessel 9 was left in a constant temperature bath for 5 minutes before pressurization.

(5) Calculation of survival rate of yeast The survival rate after pressurizing the test solution under predetermined conditions was calculated by comparing the number of viable bacteria before and after pressurization. The number of viable bacteria was directly measured by the colony count method. After diluting with sterilized deionized water so that the number of viable bacteria in the test solution becomes an appropriate number, 0.1 ml is sterilized by heating (120 ° C., 15 minutes) and then solidified by cooling (glucose 2.0% , Peptone 0.5%, yeast extract 0.3%, malto extract 0.3%). This was statically cultured in a thermostat at 30 ° C. for 72 hours, and the formed colonies were counted. The survival rate is expressed by the following formula (Equation 1), and the vertical axis of each figure showing the experimental results.

Here, N is the viable count after pressurization for a predetermined time (t), N ₀ is the viable count before pressurization, and D is the time required to reduce the viable count to 1/10. (Referred to as “D value”). The D value is used as an index representing the rate of sterilization of food such as fruit juice. The condition necessary for the sterilization of food is the ability to reduce the number of viable bacteria to 1/10 ⁵ .

(6) Measurement of sudachi juice quality before and after oxygen gas pressure sterilization About the influence on the components of sudachi juice when pressure sterilized with oxygen gas, color as appearance, D-limonene as fragrance component, and vitamin C as nutrition component Were selected as indicators and evaluated by the following methods. That is, the color tone was measured by a spectroscopic color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd.), D-limonene by a bromine-bromic acid titration method, and vitamin C by an indophenol titration method according to the Japanese Agricultural Standards Inspection Method.

2. Experimental Results (1) Sterilization of Bacteria A FIGS. 2, 3 and 4 are graphs showing the experimental results of a test solution containing Bacteria A in Sudachi juice. In the figure, the vertical axis represents the survival rate (Equation 1) of the bacterium A indicated by logarithm, and the horizontal axis represents the treatment time (minutes) of oxygen pressurization. From the figure, regarding the test solution of Bacterium A, the fruit juice temperature was set to 50 ° C. (FIG. 2), 40 ° C. (FIG. 3), and 30 ° C. (FIG. 4), and the oxygen gas alone was 0.1 MPa. The change in the survival rate of the bacteria A when changing to 0 MPa and 10.0 MPa is known. The survival rate decreases within a short time as the oxygen gas pressure and fruit juice temperature increase within the tested conditions. In the case of 50 degreeC, it was able to sterilize in about 1 minute by the pressurization of 10.0 MPa and 5 MPa. In the case of 40 degreeC, it was able to sterilize within 10 minutes by pressurization of 10 MPa, and within 10 minutes by pressurization of 5.0 MPa. In the case of 30 ° C., a pressure of 10 MPa to 5 MPa required about 10 to 15 minutes. From these results, it is shorter than the heat treatment at 65 ° C. for 10 minutes (those having a pH of less than 4.0) and 85 ° C. for 30 minutes (those having a pH of 4.0 or more), which are sterilization conditions for soft drinks. It can be seen that sterilization at time or at lower temperatures is possible.

(2) Influence on color tone by oxygen pressurization treatment Table 1 shows that the pressure of oxygen gas of 10.0 MPa is applied to Sudachi juice at a juice temperature of 20 ° C. for 30 minutes, 30 ° C. for 15 minutes, 40 ° C. for 5 minutes and 50 ° C. It shows DL * (lightness), Da * (saturation), Db * (color tone), and DE * (color difference) when comparing the color tone of the test solution before and after pressurization for 1 minute. Sudachi juice usually discolors due to oxidation when left in the air, and the absolute values of Db * and DE * increase, but under the sterilization conditions investigated, the values are small and it is found that the color tone is hardly affected.

(3) Influence on D-limonene by oxygen pressurization treatment Further, the content of D-limonene, which is an aroma component, was measured for sudachi fruit juice subjected to oxygen gas pressurization under the same conditions as the color tone comparison. The content of D-limonene was 0.105 mg / 100 ml before pressurization, but all conditions after pressurization were in the range of 0.100 to 0.110 mg / 100 ml. There was no difference. Since oxygen gas pressure sterilization can be performed at a low temperature, it is considered that the change in fragrance and color, which is a problem in heat sterilization, was suppressed.

(4) Effects of oxygen pressurization on vitamin C Usually, the degree of vitamin C content as a nutrient is not so important for sudachi juice, which is intended for flavoring in foods, but the change in quality due to oxygen pressurization In order to confirm the presence or absence, the influence of oxygen pressurization on the vitamin C content in sudachi juice was examined. The results are shown in Table 2. That is, Table 2 shows the change in vitamin C content and residual rate in fruit juice before and after oxygen pressurization and the sterilization conditions of soft drinks stipulated in the Food Sanitation Law at 65 ° C for 10 minutes (pH less than 4.0) ) And a change in vitamin C content in the fruit juice heated at 85 ° C. for 30 minutes (pH 4.0 or more). According to this, in each temperature condition, the residual rate tends to decrease slightly as the pressure increases, but 86.3% and 78.3 are obtained by pressurizing treatment for 1 minute at 50 ° C., 5 MPa, and 10 MPa, respectively. The sterilization conditions for soft drinks under normal pressure are approximately the same as 80.0% at 65 ° C. and 74.5% at 85 ° C. In addition, at 40 ° C., the pressure treatment for 5 minutes under the conditions of 5 MPa and 10 MPa shows a low tendency of 64.8% and 48.6%, respectively. It was confirmed that the effect of the pressure on the vitamin C content was relatively minor.

  The sterilization treatment method for fruit juice can be either a batch type or a continuous type. FIG. 6 shows an example of a batch-type sterilization method. A high-pressure vessel 9 connected to an oxygen gas source and a sterilized fruit juice storage tank 10 are provided. The high-pressure vessel 9 is equipped with a safety valve 11 and other equipment necessary for a high-pressure vessel. Oxygen gas is used as a pressure medium used for directly pressurizing fruit juice, and is supplied by a commercially available oxygen gas cylinder or tank truck. Further, the high-pressure tank 9 is provided with a stirring device 12 for increasing the dissolved oxygen concentration of the fruit juice and a heating / warming jacket 14 for keeping the temperature of the juice during pressurization constant.

  The fruit juice is put into the high-pressure vessel 9, and the fruit juice is directly pressurized with oxygen gas. The oxygen pressure is 5 MPa to 10 MPa, and the fruit juice temperature is 40 ° C. or higher and 50 ° C. or lower. The treatment time depends on the amount of treatment, but a short time is preferable, and at most about 10 minutes or less, more preferably 5 minutes or less. By adding agitation during pressurization, the yeast prevents precipitation separation and increases the dissolved oxygen concentration in the fruit juice to effectively exert the bactericidal effect. Depressurization after oxygen pressurization is slowly reduced by opening the gas vent and returned to normal pressure. The fruit juice thus sterilized is dispensed to the fruit juice storage tank 10 after sterilization. After the sterilization step of the present invention, the dissolved oxygen in the fruit juice is subjected to a method of degassing under reduced pressure or a bubbling treatment with an inert gas as necessary to eliminate the influence of dissolved oxygen.

  An example of a continuous sterilization method is shown in FIG. A fruit storage tank 15 before sterilization and a fruit storage tank 25 after sterilization are provided, and at least a liquid feed pump 16, a heating device 17, an oxygen gas supply device 18, an agitation and mixing device 19, an oxygen gas source are provided between the two tanks. And an oxygen gas compression device 20, a fruit juice storage deaeration device 21, a liquid feed pump 23, and a cooling device 24. Each pipe is provided with a safety device and a backflow prevention device (not shown).

  The heating device 17 only needs to be a heat exchanger, and for example, a plate heater is used, and the fruit juice can be heated and adjusted to at least 40 ° C. or more and 50 ° C. or less. The oxygen gas is supplied by a commercially available oxygen gas cylinder or tank truck. Moreover, when recovering and using oxygen after use, the oxygen gas compression apparatus 20 is used. This apparatus is a compression pump capable of adjusting the pressure of oxygen gas to at least 5 MPa to 10 MPa. The oxygen gas supply device 18 is a device for press-fitting at least 5 MPa to 10 MPa oxygen gas into fruit juice, and an oxygen gas injection device can be used. The stirring and mixing device 19 only needs to have a function of stirring and mixing fruit juice and oxygen, but a device having both pressurization and stirring functions, for example, an in-line mixer can be used. The liquid feed pumps 16 and 23 can use a method other than the pump, such as a drop or a pressure feed by pressurization. However, the liquid feed amount can be adjusted to ensure the pressure and processing time required for sterilization. The fruit juice storage tank 21 that receives the fruit juice after sterilization is a flash chamber having a function of depressurizing oxygen after use to return it to normal pressure. Oxygen that has become normal pressure can be discharged into the atmosphere through a deaeration device, but can be returned to the oxygen gas compression device 19 for circulation. Further, the fruit juice storage and deaeration device 21 has an oxygen replacement function with an inert gas.

  In the continuous processing method described above, the fruit juice sterilization process and sterilization conditions are as follows. The pressurizing process for bringing fruit juice into direct contact with oxygen gas is performed while passing through the oxygen gas supply device 18 and the stirring and mixing device 19. The fruit juice is preheated to a temperature of 40 ° C. to 50 ° C. by the heating device 17 and injected into the oxygen supply device 18 before injection. On the other hand, oxygen gas is injected into the oxygen supply device 18 from an oxygen supply source at a pressure of 5 MPa to 10 MPa. Fruit juice and oxygen are stirred and mixed by their own flow in the in-line mixer of the stirring and mixing device 19, the concentration of dissolved oxygen is increased, and sterilization is efficiently performed within a short time. The temperature of the juice during processing is kept at 40 ° C to 50 ° C. The flow rate of the juice is adjusted so that the processing time of the juice in this step is about 1 minute. Thereafter, the fruit juice is deaerated in the fruit juice storage tank 21 after sterilization, and stored in the fruit juice storage tank 25 after sterilization via the discharge pump 23 and the cooling device 24.

(Reference example)
As a basic experiment leading to the present invention, the present inventors have used Saccharomyces cerevisiae (IFO), which is generally used as an indicator bacterium, using nitrogen and oxygen as a pressure medium for confirming the bactericidal effect of oxygen pressurization. The following experiment was conducted using 10149, hereinafter referred to as “bacteria B”. The pressurizing apparatus described in the paragraph “0024” was used as the pressurizing apparatus.
(1) Preparation of test solution for bacteria B
After inoculating a refrigerated and stored bacterium B in a YPD medium (glucose 2.0%, peptone 2.0%, yeast extract 1.0%) sterilized by heating (120 ° C., 15 minutes), then kept at 30 ° C. Shake culture in a bath for 72 hours until stationary phase of growth. This culture solution was diluted 20-fold with YPD medium and cultured with shaking at 30 ° C. for 6 hours, and then the number of bacteria was adjusted by adjusting OD ₆₆₀ (turbidity at a wavelength of 660 nm by a spectrophotometer) to 0.8. When used in the experiment, the test solution was diluted 2-fold with YPD medium. Preliminary experiments show that yeast cultured for 6 hours after diluting the stationary phase culture solution 20 times with YPD medium is in the logarithmic phase of growth, and the bacterial suspension with OD ₆₆₀ adjusted to 0.8 has a bacterial count. It was confirmed that the density was approximately 5 × 10 ⁶ cells / ml.

(2) Sterilization of Bacteria B FIG. 5 is a graph showing the test results of Bacteria B. In the figure, the vertical axis represents the logarithmic survival rate (Equation 1), and the horizontal axis represents the oxygen pressurization treatment time (hours). From the figure, the YPD medium temperature was set to 50 ° C. for the test solution of Bacteria, and the pressure was increased with a mixed gas of oxygen gas and nitrogen gas so that the total pressure was 10.0 MPa, and the partial pressure of oxygen gas was 0. It can be seen that the survival rate change of the bacteria B when changed to 0.0, 2.5, 5.0, 7.5, and 10.0 MPa. The survival rate decreases in a short time as the oxygen gas pressure and the YPD medium temperature increase. The survival rate could be reduced to 1/10 ⁶ in about 15 minutes at 50 ° C. under a pressure of 10.0 MPa to 5 MPa. That is, it was revealed that direct pressurization with oxygen gas can effectively sterilize not only bacteria A but also general yeasts. In addition, since this reference example was performed in a nutrient medium (YPD medium), it took a long time for sterilization compared to Sudachi juice.

(3) Difference in sterilizing effect between nitrogen pressurization and oxygen pressurization Also, within the range of the experiment shown in FIG. 5, the survival rate of fungus B decreases rapidly as the oxygen partial pressure increases. The higher the partial pressure, the less the survival rate decreases. When the partial pressure of nitrogen gas is 7.5 MPa, the reduction is about 1/10 ⁴ even after 2 hours of processing time. Furthermore, when the pressure of nitrogen gas alone is 10 MPa, the processing time is 5 hours later. the survival rate has remained in the reduction of up to about one-tenth ^2. That is, it can be said that the bactericidal effect cannot be expected by pressurization with air of about 10 MPa. From the above results, it has been clarified that the effect of oxygen pressurization on the yeast is not a simple pressure effect but is derived from oxygen itself.

  As detailed above, according to the method of the present invention, fruit juice can be sterilized in a short time without using high temperature / ultra-high pressure, so in the field of agricultural products processing, especially in the production process of citrus citrus juice. Can be used effectively.

It is a conceptual diagram which shows the example of the high voltage | pressure apparatus used for the sterilization test of fruit juice. It is a graph which shows the relationship between the survival rate of microbe A, and the pressure and pressurization time of oxygen pressurization at 50 degreeC fruit juice temperature. It is a graph which shows the relationship between the survival rate of microbe A, the pressure of oxygen pressurization in the fruit juice temperature of 40 degreeC, and pressurization time. It is a graph which shows the relationship between the survival rate of microbe A, and the pressure and pressurization time of oxygen pressurization at 30 degreeC fruit juice temperature. It is a graph which shows the relationship between the survival rate of microbe B, and the pressurization pressure and pressurization time with nitrogen and oxygen at a YPD medium temperature of 50 ° C. It is a conceptual diagram which shows the sterilization processing method of the fruit juice by a batch type. It is a conceptual diagram which shows the sterilization processing method of the fruit juice by a continuous type.

1 .... High pressure cylinder for oxygen 2 .... High pressure cylinder for nitrogen 3 .... Pressure control valve
4 ... Pressure gauge
5 ... Pressure display
6 ················································ Relief valve , 25... Fruit juice storage tank after sterilization 11... Safety valve 12... Stirring device 13, 16, 23.・ ・ ・ Jacket 15 ・ ・ ・ ・ ・ ・ ・ ・ Fruit storage tank 17 ・ ・ ・ ・ ・ ・ ・ ・ Heating device (Heat exchanger plate heater)
18 ... Oxygen gas supply device (oxygen gas injection device)
19 ... Stir and mix device (in-line mixer)
20 ... Oxygen gas compression device 21 ... Fruit juice storage tank after sterilization (flash chamber)
22, 24 ... Cooling device (heat exchanger plate heater)

Claims (4)

A method for sterilizing fruit juice using both pressurization and heating, wherein fruit juice at a temperature of 60 ° C. or less is subjected to pressure treatment by directly contacting oxygen , and the pressure of the pressure treatment is 5 MPa or more and 10 MPa or less. A method for sterilizing fruit juice, comprising: The method for sterilizing fruit juice according to claim 1, wherein the temperature of the fruit juice is 40 ° C or higher and 50 ° C or lower. Claim 1 or claim 2 method of sterilizing the juice according to any one fruit juice is Kosan citrus juice. The method for sterilizing fruit juice according to claim 3 , wherein the citrus citrus is sudachi.

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