JP5912662B2 - Sterilization method of liquid food - Google Patents

Description

  The present invention relates to a method for sterilizing a liquid food using both an alternating electric field treatment and a pasteurization treatment.

Conventionally, AC electric field treatment and pasteurization treatment have been performed as a method of sterilizing (sterilizing) the flavors of liquid foods such as milk, fruit juice, soup and drinking water and vitamins and other useful ingredients without breaking them as much as possible. .

The AC electrolysis treatment includes AC high electric field treatment (about 20 kHz) and short-wave band AC electric field treatment (about 27 MHz) depending on the frequency to be applied, and specific prior arts include Patent Documents 1 to 4.

In Patent Document 1, when the current flowing between the electrodes is I (ampere), the distance between the electrodes is G (mm), and the area of the facing surface of each electrode is S (mm2), I / G × S1 / 2 ≦ 2.0 is described, and Patent Document 2 describes that the pressure in the energizing unit is 0.45 to 0.95 MPa, and the applied voltage per electrode distance (V / cm). ) × application time (seconds) ≧ 50 is described to be controlled, and Patent Document 3 and Patent Document 4 describe that the filtration process is performed a plurality of times prior to the AC high electric field process. .

The pasteurization treatment is a method of treating at a relatively low temperature for a long time (for example, 30 minutes) at which denaturation of proteins or the like does not occur, and specific prior arts include Patent Documents 5 and 6.

Patent Document 5 describes that a microorganism in raw milk is sterilized at a low temperature by a flow path type holding sterilization apparatus, and heat treatment of whey protein in milk components is kept low and heat treatment is performed. In addition, it is described that milk is led to a steam heating part of a heat exchanger through a homogenizer, and is reheated (65 ° C.) to be pasteurized.

JP 2006-197887 A JP 2006-238827 A JP 2007-29012 A JP 2007-29014 A Japanese Patent Laid-Open No. 5-130831 JP-A-8-322463

  In the case of AC electric field treatment as disclosed in Patent Documents 1 to 4, if the outlet temperature of the liquid food is higher than the critical temperature of bacteria (heat-resistant spore bacteria), the inactivation rate of bacteria is high in proportion to the outlet temperature. Become. However, when the deactivation rate is about 3 log order, the bactericidal effect is saturated, and it is difficult to increase the deactivation rate without affecting the quality of the liquid food.

As a result of intensive studies on heat-resistant spore bacteria, the present inventors are more effective for sterilization in AC electric field treatment than heat treatment spore bacteria with a heat treatment exceeding the critical temperature inherent to heat-resistant spore bacteria. In addition, it was found that the heat-resistant spore bacteria that were once thermally damaged are likely to be killed by subsequent low-temperature heating.

The present invention has been made on the basis of the above findings, and an AC electric field having a frequency of 20 kHz to 50 MHz is applied to the liquid food, and the induced current flowing in the liquid food causes the liquid food to be shorter than the critical temperature of the microorganism to be sterilized. After being raised for a period of time, an AC electric field treatment for immediately cooling is performed, and this AC electric field treatment is followed by a low-temperature heat treatment at 80 ° C. or lower.

In the AC electric field treatment, the liquid food flows between a pair of electrodes under pressure (for example, 0.6 MPa) at a constant speed (for example, 600 mL / min), and the outlet temperature with a short application time (for example, 0.4 seconds). Becomes 120 ° C. Moreover, the conditions of low temperature heating shall be 30 minutes-10 seconds at 65-80 degreeC, for example.

In addition, when performing AC electric field treatment, liquid foods that do not contain proteins such as coffee, tea, fruit juice are subjected to AC high electric field treatment as the AC electric field treatment, and liquid foods containing proteins such as milk and gravy In this case, short-wave AC electrolysis is performed as the AC electric field treatment.

Furthermore, microorganisms to be sterilized include all microorganisms such as vegetative cells such as Escherichia coli and yeast, heat-resistant spore bacteria, and molds.

  According to the present invention, the sterilization effect of microorganisms in liquid food is greatly enhanced as compared with conventional ones without impairing the flavor of the liquid food and without modifying the active ingredients such as vitamins and proteins in the liquid food. be able to.

For example, it is possible to produce milk having the quality of pasteurized milk while performing sterilization equivalent to long-life milk.
Moreover, since the milk sterilized by the method of the present invention has less heat denaturation of protein and high safety, the added value of the processed milk product is improved.

Schematic general view of an apparatus used for carrying out the method for sterilizing liquid food according to the present invention The perspective view explaining the structure of the alternating current high electric field processing apparatus The perspective view explaining the structure of the short-wave-band AC electric field processing device Graph showing sample temperature history Graph showing the relationship between incubation time and number of colonies Graph showing the electrode outlet temperature of milk and the residual rate of Bacillus subtilis spores Graph showing soymilk electrode outlet temperature and Bacillus subtilis spore survival rate

In the following, preferred embodiments of the present invention will be described.
FIG. 1 is a schematic overall view of an apparatus used for carrying out a method for sterilizing a liquid food according to the present invention. An AC high electric field treatment apparatus 2 is provided downstream of a raw material tank 1, and the liquid in the raw material tank 1 is supplied by a pump 3. Food is sent in. An AC power supply 4 having a frequency of 20 kHz is connected to the AC high electric field processing apparatus 2.

  As shown in FIG. 2, the AC high electric field processing apparatus 2 is provided with a ring-shaped electrode 6 around a cylindrical flow path 5. When the liquid food passes through the flow path 5, it is heated to about 80 ° C. by Joule heat.

  A short wave band AC electric field processing device 7 is arranged downstream of the AC high electric field processing device 2, and an AC power supply 8 having a frequency of 27 MHz is connected to the short wave band AC electric field processing device 7. A thermometer 9 is provided in the pipe connecting the AC high electric field processing device 2 and the short wave band AC electric field processing device 7.

  As shown in FIG. 3, the short-wave band AC electric field processing device 7 forms a flow path by arranging two narrow blocks 12 and 12 with an interval between the upper and lower blocks 10 and 11. ing. The block itself is made of Teflon (registered trademark), or the surface constituting the flow path is coated with Teflon (registered trademark). The upper and lower blocks 10 and 11 are provided with electrodes 13 and 14, respectively. The liquid food is instantaneously heated to 120 ° C. or higher by applying a short-wave AC electric field to the liquid food flowing in the flow path via the electrodes 13 and 14.

  A cooler 15 is disposed on the downstream side of the short-wave band AC electric field treatment device 7, and a thermometer 16 is provided in a pipe connecting the cooler 15 and the short-wave band AC electric field treatment device 7. The cooler 15 cools the liquid food to about 40 ° C. in a short time.

  A pressure gauge 17 and a pressure adjustment valve 18 are provided on the downstream side of the cooler 15, and the liquid food subjected to the alternating electric field treatment is sent to the hot tub 19 for low-temperature heat treatment via the pressure adjustment valve 18.

In the above, for the liquid food product comprising a protein, such as milk and instantaneously heated with short wave alternating electric field treatment device 7 prevent protein denaturation, proteins such as coffee respect that does not contain liquid food May be heated to a critical temperature or higher using the AC high electric field treatment device 2 without using the short wave AC electric field treatment device 7.

  FIG. 5 is a comparison of the number of colonies when incubating Bacillus subtilis in a sample that has been subjected only to Joule heating and a sample that has been subjected to short-wave band treatment. Since instantaneous heating using the band AC electric field treatment device 7 has an effect of slowing the rate of increase in the number of colonies, it is preferable to use both in combination.

  Using the above processing apparatus, a liquid food obtained by adding a spore solution to milk was prepared, and the milk was allowed to flow at a constant rate (600 mL / min). As shown in FIG. 4, the AC high electric field treatment apparatus 2 heated milk from 10 ° C. to 80 ° C. in 4 seconds. Next, this milk was heated to 120 ° C. in 0.4 seconds by applying a short-wave alternating current of 27 MHz and a maximum output of 5 kW.

  Thereafter, the temperature of the milk is lowered to 40 ° C. over 4 seconds with the cooler 15, and the test tube containing the milk with the lowered temperature is immersed in a 65 ° C. hot tub (constant temperature bath) for 30 minutes, Sterilized.

FIG. 6 is a graph showing the inactivation rate of Bacillus subtilis spores when only short-wave AC electric field treatment is performed on milk and when short-wave AC electric field treatment and low-temperature treatment are used in combination.
From this graph, the deactivation rate is saturated in the order of 3 logarithm in the case of only the short-wave band AC electric field treatment, but it can be seen that the deactivation rate is deactivated by 5 logarithm order or more without saturation by using low temperature treatment together. .

Fig. 7 shows the rate of inactivation of Bacillus subtilis spores when soy milk is subjected to only short-wave AC electric field treatment under the same conditions as the experiment performed on milk and when both short-wave AC electric field treatment and low-temperature treatment are used in combination. It is the graph which showed.
From this graph, the deactivation rate is saturated at 3 logarithmic orders only when the short-wave band AC electric field treatment is used. However, when the low temperature treatment is used later, the deactivation rate is deactivated by 5 logarithmic orders or more without saturation. I understand.

  Thus, when combined with low-temperature treatment later, the deactivation rate is higher than when each is applied alone. When an alternating electric field is applied to the liquid food flowing between the electrodes, an induced current flows in the liquid food. As a result, the liquid food can be raised within a short time by the induced current above the critical temperature of the microorganisms to be sterilized. This treatment kills or takes damage. And many microorganisms damaged by the low-temperature heat processing below 80 degreeC performed after that will be killed.

  From the above, as a sterilization method for liquid food, the effect of pasteurization is increased by first thermally damaging microorganisms by AC electric field treatment and then performing pasteurization. In particular, if both AC high electric field processing and short wave AC field processing are performed as AC electric field processing, the effect is further enhanced.

  The method for sterilizing a liquid food according to the present invention can be used for sterilization of all liquid foods such as milk, coffee, fruit juice, tea and soup.

  DESCRIPTION OF SYMBOLS 1 ... Raw material tank, 2 ... AC high electric field processing apparatus, 3 ... Pump, 4 ... AC power supply, 5 ... Flow path, 6 ... Ring-shaped electrode, 7 ... Short wave band AC electric field processing apparatus, 8 ... AC power supply, 9 ... Thermometer, 10 ... upper block, 11 ... lower block, 12 ... narrow block, 13, 14 ... electrode, 15 ... cooler, 16 ... thermometer, 17 ... pressure gauge, 18 ... pressure regulating valve, 19 ... temperature Bathtub.

Claims (2)

A method of applying an alternating electric field having a frequency of 20 kHz to 50 MHz to a liquid food and sterilizing the liquid food by an induced current flowing in the liquid food, and subjecting the liquid food containing proteins such as milk and gravy to Joule heat treatment Heat treatment to 80 ° C., followed by heat treatment at 120 ° C. or more in a shorter time than the Joule heat treatment by short-wave AC electric field treatment, followed by cooling treatment following this heat treatment, A method for sterilizing a liquid food, characterized by performing a low-temperature heat treatment at 80 ° C. or lower following the cooling treatment . The method for sterilizing a liquid food according to claim 1, wherein the microorganisms to be sterilized include vegetative cells such as Escherichia coli and yeast, heat-resistant spore bacteria, and mold.

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