JPH04144656A - Method for sterilizing rice cake - Google Patents

Abstract

PURPOSE:To carry out sterilization in a short time without causing quality deterioration of rice cake by subjecting rice cake to microwave heating while stirring and transferring the rice cake in a pipe and simultaneously carrying out heat sterilization under inner pressure control. CONSTITUTION:Rice cake produced through ordinary each process is charged into a hopper and continuously fed to a pipe type microwave heating device by a transfer pump. Then the rice cake is irradiated with microwave while stirring and carrying the rice cake in a pipe and simultaneously subjected to inner pressure control corresponding to sterilizing temperature and time so as to retain the inside to sterilizing temperature and time and subjected to heat sterilization in a condition of F0 value of 5-25 and the sterilized rice cake is taken out and sealed and packaged in a germ-free condition in a clean room.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for sterilizing rice cakes, and more particularly to a method for sterilizing rice cakes that can be sterilized for a short period of time without causing deterioration of the quality of the rice cakes.

[Conventional technology] Traditionally, freshly pounded mochi is a product with a high water content (high water activity) that contributes to the growth of microorganisms, so it is impossible to store the mochi for a long time at room temperature simply by packaging it. However, in recent years, the use of clean room equipment and the use of oxygen absorbers has made it possible to prevent mold from forming even when stored at room temperature.
It is now possible to distribute the product at room temperature for about one month.

[Problem to be solved by the invention] However, even if the rice cake is packaged in the manner described above, it was not possible to sterilize the initial germs before the mochi was pounded, and it was not possible to store the rice cake for a longer period of time at room temperature. .

On the other hand, a method of heat sterilization using a heating means such as retort sterilization is also used, but in this method, for example, C, b
In order to sterilize even heat-resistant bacteria such as P. otulinum, long-term heating is required, causing problems such as browning of the mochi (browning) and loss of texture, resulting in a decrease in product value. . The above-mentioned sterilization effect and browning are influenced by the heating temperature and time.

The present invention was made in view of these conventional problems to be solved, and its purpose is to provide a method for sterilizing rice cakes that can be sterilized for a short period of time without causing quality deterioration.

[Means for Solving the Problems] In order to achieve the above object, the rice cake sterilization method of the present invention includes the following steps:
Mochi made through processes such as rice polishing, rice washing, soaking, steaming, and mochi pounding (or kneading) is put into a hopper, and is continuously transferred by a conveying pump and introduced into a pipe-type microwave heating device. The material is irradiated with microwaves while being stirred and transferred, and the corresponding internal pressure is controlled to maintain the sterilization temperature and time, and heat sterilization is performed under conditions such that the F0 value is 5 or more and 25 or less, and then taken out. It is said that

According to the present invention, heat-resistant bacteria can also be sterilized by high-temperature sterilization using microwave heating, making it possible to produce rice cakes that can be stored for a long time.
For example, since the rice cake does not change color, change its taste, or change its physical properties, there is no inconvenience that the product value decreases.

The present invention will be explained in detail below.

FIG. 1 is an explanatory diagram of an example of an apparatus used to carry out the rice cake sterilization method of the present invention.

The rice cake that is to be sterilized is processed through conventional rice polishing, washing, soaking, steaming,
It is manufactured through the various steps of mochi pounding (or kneading). The sterilization method of the present invention can of course be applied to sterilize freshly pounded mochi produced in this way, but it can also be used to recycle excess production such as chips and offering mochi produced in the conventional production of cut mochi. It can also be applied to sterilize returned rice cake.

First, rice cakes are put into hopper 1 as shown in Figure 1.
Continuously transferred through the pipe 3 by the transfer pump 2. In addition, it is desirable that the rice cakes put into the hopper 1 be in a state of 80 to 100° C. to prevent uneven heating due to microwave heating.

In this way, the rice cake is introduced into the pipe type microwave heating device 4. The microwave heating device 4 sterilizes the rice cakes by irradiating them with microwaves from outside the pipe through which the rice cakes are transferred, using the heat generated by the rice cakes themselves.
Those shown in the publication can be used. A pipe disposed in the microwave heating device 4 is made of a microwave-permeable material such as Teflon, and a rotating screw is disposed inside the pipe, so that the rice cake is stirred and transferred within the pipe. With this microwave heating device 4, the rice cake is finally heated to a predetermined temperature by microwave irradiation so that the sterilization value Fo, which is determined by the factors of temperature and time required for sterilization, is in the range of 5≦F0≦25. Then, in a holding section 5 following the microwave heating device 4, it is held for a predetermined period of time. Note that the corresponding control of the pressure inside the pipe to maintain it at the sterilization temperature is performed by the conveying pumps 2.6 before and after the microwave heating device 4.

Generally, the effectiveness of heat sterilization is determined by the product of the logarithm of the heating time and the heating temperature, and the sterilization value at 121.1°C:
Represented by Fo. This F0 value varies depending on the type of target bacteria, the water activity of the target food, and the pH, but in general, it contains C, botul, which produces toxins and causes food poisoning.
Inum is used as an index. The present invention is based on this principle to determine the F0 value necessary for sterilizing rice cakes. In other words, a logarithmic graph (see Figure 3) with temperature on the horizontal axis and logarithm of time (minutes) on the vertical axis shows C, b as stipulated in the Food Sanitation Act.
Draw a Fi convex curve fl) for sterilization conditions satisfying 120°C and 4.0 minutes for P. otulinum, then plot the results of the examples described later, and translate the Fi convex curve in parallel to obtain the sterilization effect. The range (f2) in which

The F0 value at this time was F0≧5. Furthermore, since browning is also estimated to be determined by the heating time and heating temperature in the same way as the sterilizing effect, the range (f3) in which browning does not occur was determined in the same manner as above. When this condition was replaced with the above F0 value, it was found that F0≦25. Therefore, in sterilizing rice cakes, it was found that the range in which a sufficient sterilizing effect can be obtained and browning does not occur is 5≦F0≦25.

In addition, rice cakes can be sterilized by heating, which is equivalent to conventional retort cooking.
If the rice cake is heated at a temperature exceeding 110 to 120° C. for a long time of about 20 minutes or more, the structure of the rice cake will be divided, the moisture content, etc. will change, and the texture will tend to deteriorate. From this point of view as well, conventional retort sterilization is not preferable.

In the present invention, the above-mentioned problem does not occur because a sufficient sterilization effect can be obtained by heating for about 5 minutes. Note that, also from the standpoint of device design, the heating time (in the holding portion) in the present invention is preferably 5 minutes or less. To enable heating for a longer time than this requires the holding portion to be longer, which is uneconomical. On the other hand, shortening the holding portion requires raising the heating temperature, but raising the temperature too high is not preferable because it is difficult to obtain uniform heating conditions. Therefore, it is preferable that the heating time be at least 1 minute or longer.

The rice cakes sterilized in this way are taken out and sterilized and sealed in a clean room, for example, to complete packaged rice cakes.

Furthermore, FIG. 2 shows another example of an apparatus used to carry out the rice cake sterilization method of the present invention, in which a pressure regulating valve 7 is used in place of the conveying pump after the microwave heating apparatus 4. It is.

[Example] Hereinafter, the present invention will be described in more detail with reference to Examples.

According to the usual process, rice is polished, washed and soaked in water (2 hours), and steamed (100-105℃, 25 minutes).
After incubating 10' li-nun+ spores/g, Kinetsuki mochi was produced by the conventional method, and the first stage was incubated at 85-90°C.
It was put into the hopper shown in the figure. With the conveyor pump, 30
The material was transferred through the pipe at 0 kg/H, introduced into a microwave heating device (12 units of irradiation output magnetron 1.3 kW), and sterilized under the conditions shown in the table below. In the final removal process, it was kneaded aseptically into a sterile cup. I collected rice cakes. After rapidly freezing the collected rice cake dough, a microbial test was conducted according to a conventional method, and the appearance and texture of the rice cake were also observed, and the results shown in the table below were obtained.

For comparison, a packaged rice cake that had been retort sterilized was also evaluated in the same way.

Margin below As shown in the above results, No. 3.4.7.8.11 having an F0 value of 5 or more and 25 or less has a sufficient bactericidal effect and does not have the problem of browning. The texture of the rice cake after processing is
The one of the present invention had no problems at all, but No. 13 (
135℃, 5 minutes), the original elasticity of mochi is lost,
It was candy-like. Also, no.

Samples No. 14 and 15 (retorted), like No. 13, lost their elasticity and became candy-like, and also had a strange odor similar to that of sweet potatoes.

[Effects of the Invention] As explained in detail above, according to the method for producing rice cake of the present invention, sufficient sterilization is performed to enable long-term storage,
Furthermore, it has the excellent effect of not causing any quality deterioration due to sterilization, such as discoloration, change in taste, or change in physical properties of the rice cake. Therefore, if the present invention is used, it is possible to produce rice cakes that can be stored for a long period of time without the disadvantage of decreasing commercial value due to conventional heat sterilization.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of examples of apparatus used to carry out the rice cake killing method of the present invention, respectively, and FIG. 3 is a graph showing the relationship between the logarithm of heating time and heating temperature. 1... Hopper 2... Conveying pump 3... - Pipe 4... Pipe type microwave heating device 5... Holding section 6... Conveying pump 7... Pressure regulating valve

Claims (1)

[Claims] Mochi made through processes such as rice polishing, rice washing, soaking, steaming, and mochi pounding (or kneading) is put into a hopper, and is continuously transferred by a conveying pump and introduced into a pipe-type microwave heating device. The material is irradiated with microwaves while being stirred and transferred, and the corresponding internal pressure is controlled to maintain the sterilization temperature and time, and heat sterilization is performed under conditions such that the F_0 value is 5 or more and 25 or less, and then taken out. A method of sterilizing rice cakes.