Method for sterilizing rice flour

Abstract

To provide a sterilization method of rice flour which is capable of reducing the number of general bacteria to 10000 / g or less without spoiling flavor or taste of rice flour.SOLUTION: The sterilization method of rice flour can reduce the number of general bacteria to 10000 / g or less by low-temperature sterilization treatment without spoiling the flavor or taste of rice flour by: a loading process S102 of loading bags filled with rice flour spaced at a predetermined distance; a sterilization process S104 of sterilizing loaded rice flour at the temperature of 68°C to 75°C and the humidity of 40% to 60% for 13.5 hours to 16 hours; and a temperature-dropping process S106 of dropping the temperature of rice flour after sterilization treatment under a predetermined condition to prevent occurrence of condensation. Thus, rice flour with excellent food sanitation can be provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for low-temperature sterilization of rice flour.

Background Art

[0002] In recent years, due to the increasing awareness of food hygiene, there have been many cases where even wheat flour and rice flour that basically do not allow bacteria to grow are required to meet the standard of 10,000 or less per gram, which is the microbial standard for other foods. In addition, as a conventional sterilization method for powders, high-temperature sterilization and superheated steam sterilization described in the following [Patent Document 1] are generally known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the high-temperature sterilization method and the superheated steam sterilization method may damage the flavor and taste of cereal flours such as rice flour due to high-temperature treatment and water adhesion, and are not preferable.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a sterilization method for rice flour capable of reducing the general bacterial count to 10,000 or less per gram without damaging the flavor and taste of the rice flour.

Means for Solving the Problems

[0006] The present invention is (1) A sterilization method for rice flour, comprising a stacking step S102 of stacking bags filled with rice flour at predetermined intervals, a sterilization step S104 of subjecting the stacked rice flour to sterilization treatment at a temperature of 68°C to 75°C and a humidity of 40% to 60% for 13.5 hours to 16 hours, Rice flour after sterilization treatment Lower It has a temperature reduction step S106 for preventing the occurrence of warming and condensation it The temperature reduction step S106 includes a first temperature reduction step S106A in which the humidity is 30% - 35% and the temperature is 48°C - 55°C over 2 to 3 hours from the end of the sterilization step S104, and a second temperature reduction step S106B in which the temperature is 25°C - 30°C at the same humidity as the sterilization step S104 over 2 to 3 times the time of the first temperature reduction step S106A, and is performed in two stages By providing a method for sterilizing rice flour characterized by the above, the above problems are solved. (2) By providing the method for sterilizing rice flour according to (1) above, wherein the loading step S102 loads the bags filled with rice flour in a windmill type stacking with a predetermined interval, the above problems are solved. 。

Effects of the Invention

[0007] The method for sterilizing rice flour according to the present invention can reduce the general bacterial count to 10,000 CFU / g or less by a low-temperature sterilization treatment that does not damage the flavor and taste of the rice flour by optimizing the treatment temperature, treatment humidity, treatment time, and loading method. Thereby, it is possible to provide rice flour that is excellent in food hygiene.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] The method for sterilizing rice flour according to the present invention will be described with reference to the drawings. First, as shown in the flowchart of FIG. 1, the method for sterilizing rice flour according to the present invention includes a stacking step S102 of stacking bags filled with rice flour at a predetermined interval, a sterilization step S104 of sterilizing the stacked rice flour, and a temperature reduction step S106 of reducing the temperature of the sterilized rice flour under predetermined conditions to prevent the occurrence of condensation. The temperature reduction step S106 is performed in two stages, a first temperature reduction step S106A and a second temperature reduction step S106B, as will be described later. etc.

[0010] In addition, the method for sterilizing rice flour according to the present invention basically assumes that after the rice flour is packed in a packaging bag, the sterilization is performed for each bag. With this configuration, the handling of the rice flour is easy, and bacterial contamination in the subsequent process can be avoided. Also, generally, since the water activity of powder is low, bacteria cannot grow, and by performing the sterilization treatment after sealing in the bag, bacteria basically do not increase until the bag is opened, but rather show a decreasing trend.

[0011] Next, the condition setting of the sterilization step S104, which is a characteristic configuration of the present invention, will be described. First, as an experiment on a small scale, rice flour filled in a 1 kg packaging bag was sterilized at temperatures of 60 °C, 70 °C, and 80 °C for 4 to 16 hours, and the total viable count was measured. The total viable count was randomly sampled at 4 points for each condition and measured according to well-known inspection standards. The results are shown in FIG. 2. Here, the horizontal axis in FIG. 2 is the treatment time, and the vertical axis is the value of the maximum total viable count (MAX value) among the measured samples under the same conditions. From this FIG. 2, it can be seen that the sterilization effect improves as the treatment temperature increases. Also, it can be seen that the sterilization ability improves significantly between the treatment temperatures of 60 °C and 70 °C. From the results of FIG. 2, it can be seen that in order to achieve a total viable count of 10,000 cells / g or less in a 1 kg bag of rice flour, 10 hours or more are required at a treatment temperature of 60 °C, while 4 hours are sufficient at treatment temperatures of 70 °C and 80 °C. However, if the temperature exceeds 80 °C, there is a risk of damaging the flavor of the rice flour, etc., so the treatment temperature is preferably 68 °C to 75 °C near 70 °C.

[0012] Regarding the processing humidity, no significant change in the moisture content of the rice flour was observed at a humidity of 40% - 60%. However, when the processing humidity was less than 30%, the moisture content of some of the rice flour decreased and became over-dried, and α - conversion was also observed. Also, when the processing humidity exceeded 60%, depending on the placement position and stacking method of the bags, some of the rice flour absorbed moisture and the moisture content increased. Such fluctuations in the moisture content of the rice flour are not preferable from the perspective of maintaining the quality of the rice flour. Therefore, the humidity during the sterilization treatment is preferably in the range of 40% - 60%, and more preferably 45% - 55%.

[0013] Next, multiple 20 - kg bags of rice flour close to the actual scale were stacked on a pallet without gaps in 5 - step increments. Next, this pallet was placed in a constant - temperature and humidity chamber, and sterilization treatment was performed for 8 hours or 16 hours under the conditions of a temperature of 68°C - 75°C and a humidity of 45% - 55%. Next, the temperatures of multiple points at the center of the rice flour after the sterilization treatment were measured and samples were collected. Next, the total viable count of the collected samples was measured by a well - known method. The results are shown in Figure 3. Here, the horizontal axis in Figure 3 is the minimum value (MIN value) among the multiple rice - flour temperatures measured at the time of sample collection, and the vertical axis is the total viable count (number / g). Also, the plots enclosed by the broken line in Figure 3 are groups of samples under the same conditions.

[0014] From Figure 3, the viable count of Group A with the lowest rice flour temperature of 26.0°C varied greatly from 6,300 CFU / g to 25,000 CFU / g, and more than half of the samples exceeded the target viable count of 10,000 CFU / g. In addition, the measured temperature of the rice flour in Group A was 26.0°C to 54.4°C, and since there was a room temperature part, it is considered that a part of the rice flour was not heated and no sterilization treatment was performed. Also, all the samples of Group B and Group C had viable counts below the target of 10,000 CFU / g. In addition, the temperature of the rice flour in Group B was 44.1°C to 51.1°C, and the temperature of the rice flour in Group C was 54.3°C to 60.1°C. From this, it can be seen that for rice flour in powder form with a low moisture content, the viable count can be reduced to 10,000 CFU / g or less by setting the temperature to generally 44°C or higher. In addition, Group A was obtained by dividing 20 kg bags of rice flour into 2 pallets, stacking a total of 36 bags without gaps in a stepped manner, and putting them into the tank. For this reason, it is presumed that the rice flour located in the central part did not receive sufficient heat conduction and appropriate heat treatment was not performed. From these facts, it is important to perform heat treatment at a sufficient temperature on the entire rice flour for sterilization treatment, and it is necessary to consider the bag loading method for efficient sterilization treatment.

[0015] Next, 20 kg bags of rice flour were loaded in a total of 14 bags in a windmill - type stacking with 4 - layer and 4 - round with a predetermined interval and put into a constant - humidity and constant - temperature tank. The bag loading method is not particularly limited as long as there is an interval between the bags. However, in the above - mentioned windmill - type stacking, an interval is provided, so gaps are formed not only on the sides of the bags but also on a part of the upper and lower surfaces. Therefore, it is considered that heat conduction into the bags is performed more efficiently. In addition to directly stacking the bags, the bags can be loaded individually or in groups of several using a mesh rack or the like. In a configuration using such a mesh rack or the like, since the exposed part of the bag increases, more efficient heat conduction and sterilization treatment can be performed.

[0016] Next, this sample was held under the conditions of a temperature of 68°C to 73°C and a humidity of 45% to 55% for 8 hours for sterilization treatment. Note that the temperature and humidity hereafter refer to the temperature inside the tank, not the actual temperature of the rice flour. Next, the sterilized sample was collected and the total number of general bacteria was measured. The results are shown in the table of Fig. 4(a). From the results of Fig. 4(a), the total number of viable bacteria exceeded the target of 10,000 cells / g in more than half of the locations. From this, it is considered that even with staggered stacking at intervals, sufficient heating (sterilization treatment) of the entire rice flour was not performed with a heating time of 8 hours. Also, during the experiment in Fig. 4(a) and the experiment of Group A in Fig. 3, condensation occurred when the sample was taken out. Such adhesion of moisture is a major factor promoting the growth of fungi and is not preferable.

[0017] Next, 20 kg bags of rice flour were stacked in a windmill pattern with 5 layers and 4 rounds with a predetermined interval, for a total of 20 bags (40 bags in the second time), and sterilization treatment was performed at the same temperature of 68°C to 73°C and humidity of 45% to 55% as the previous conditions for 14 hours. Also, as a countermeasure against condensation, after the sterilization treatment, the first temperature reduction step S106A and the second temperature reduction step S106B were performed to cool the sample. Here, in the first temperature reduction step S106A, while setting the humidity inside the tank to 30% to 35%, the temperature inside the tank was reduced from the temperature during sterilization treatment to 48°C to 55°C in 2 to 3 hours. Note that the first temperature reduction step S106A reduces the temperature inside the tank while preventing the saturation of water vapor inside the tank and inside the rice flour bags in a relatively low humidity state. However, if the humidity is reduced too much at this time, the rice flour will dry and the moisture content of the rice flour will decrease. Therefore, the humidity in the first temperature reduction step S106A was set to 30% to 35%. Next, in the second temperature reduction step S106B, while setting the humidity to the same humidity as during sterilization treatment, 45% to 55%, the temperature inside the tank was reduced to 25°C to 30°C near room temperature in about 6 hours. Note that in the second temperature reduction step S106B, while maintaining the moisture content of the rice flour by setting the humidity to 45% to 55%, the temperature of the rice flour is reduced to near room temperature.

[0018] Then, the above test was conducted three times, and the general bacterial count of each sample was measured. The results are shown in the table of Fig. 4(b). From the results of Fig. 4(b), in the first test, the general viable bacteria count was 8,000 cells / g to 400 cells / g, in the second test it was 1,900 cells / g to 100 / g or less, and in the third test it was 7,800 cells / g to 160 cells / g. Although there was some variation, in all three tests, results less than the target of 10,000 cells / g were obtained at all locations. Also, the occurrence of dew condensation was not observed in all three tests. Here, the results of plotting the data in Fig. 4(a) and Fig. 4(b) are shown in Fig. 5. From Fig. 5, it can be seen that in order to make the general bacterial count less than 10,000 cells / g under the conditions of a temperature of 68°C to 73°C and a humidity of 45% to 55%, a treatment time of 13.5 hours or more is required. Also, since it is preferable that the treatment time is shorter, it can be said that the sterilization treatment time is preferably about 13.5 hours to 16 hours.

[0019] As described above, the sterilization method for rice flour according to the present invention can reduce the general bacterial count to 10,000 cells / g or less by an optimized low-temperature sterilization treatment that does not impair the flavor and taste of the rice flour, by optimizing the treatment temperature, treatment humidity, treatment time, and loading method. Thereby, rice flour excellent in food hygiene can be provided.

[0020] Note that conditions other than the configurations and main conditions of each step of the rice flour sterilization method shown in this example are not limited to this example, and the present invention can be implemented with modifications without departing from the gist of the present invention.

Explanation of Symbols

[0021] S102 Loading step S104 Sterilization step S106 Cooling step S106A First cooling step S106B Second cooling step

Claims

1. A method for sterilizing rice flour, comprising: a stacking step of stacking bags filled with rice flour at predetermined intervals; a sterilization step of sterilizing the stacked rice flour at a temperature of 68°C to 75°C and a humidity of 40% to 60% for 13.5 hours to 16 hours; a temperature reduction step of reducing the temperature of the sterilized rice flour to prevent the occurrence of condensation; and the temperature reduction step includes a first temperature reduction step of setting the humidity to 30% to 35% and the temperature to 48°C to 55°C over 2 to 3 hours from the end of the sterilization step; The method for sterilizing rice flour is characterized in that it is carried out in two stages, namely a second temperature reduction step of setting the temperature to 25°C to 30°C at the same humidity as the sterilization step over a time that is two to three times that of the first temperature reduction step.

2. The method for sterilizing rice flour according to claim 1, wherein the stacking step stacks the bags filled with rice flour in a windmill-like stack with predetermined intervals.

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