JP2000217521A - Production of boiled rice capable of being preserved for long period and packed boiled rice - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing boiled rice having the same qualities such as taste, texture and smell, when eaten, as those of just-boiled rice and capable of being preserved for a long period by immersing washed rice in immersion water containing adipic acid and then treating the rice under specific conditions to kill heat-resistant spore bearing bacteria. SOLUTION: This method for producing boiled rice capable of being preserved for a long period comprises immersing 12 washed rice 11 in an adipic acid- containing immersion water (the concentration and the pH value of adipic acid are preferably 0.05-1% and 4-8, respectively) for >=2 min, draining 13 the immersion water, washing 14 the immersed rice with 5-70 deg.C water, while applying an ultrasonic treatment to the immersed rice, charging 15 the washed rice in a container, adding water to the charged rice, and then applying a thermal treatment 16 to the rice mixture. It is preferable that the boiled rice is sealed 17 in a gas barrier film to prepare the packed boiled rice, and the adipic acid content and pH value of the packed boiled rice are preferably <=0.07 wt.% and 5-8, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cooked rice that can be stored for a long period of time and a packaged cooked rice. The present invention relates to a method for producing cooked rice and a packaged cooked rice prepared by packaging the cooked rice obtained by the method.

[0002]

2. Description of the Related Art
Boiled rice products called wrapped boiled rice have appeared on the market, and the sales volume has been increasing year by year. The biggest quality characteristic of this packaged rice is that it can be stored at room temperature for a long time,
In order to achieve such properties, it is necessary to sterilize or sterilize the heat-resistant spores present in rice grains to make the cooked rice commercially sterile.

[0003] As a method for disinfecting the heat-resistant spore bacterium, a method of filling rice rice in a retort pouch and sealing and heat sterilizing it (Japanese Patent Application Laid-Open No. 56-72755), or
A method of retort sterilization after filling with cooking water and immersed rice (Japanese Patent Laid-Open No. 62-59959) and the like are disclosed.
In each case, heat treatment is different from normal rice cooking,
The appearance, aroma and taste are inferior to ordinary cooked rice, and the quality is far from freshly cooked rice.

On the other hand, as a bacteriostatic method for heat-resistant bacteria, an edible organic acid is added to immersion water or cooking water to adjust the pH of cooked rice after cooking.
(JP-B-7-89879) discloses a method of controlling (bacteriostatic) the growth of heat-resistant spores that could not be killed by heating during rice cooking by adjusting the pH to 4.0 to 4.8. .

[0005] As a method of using retort sterilization and a pH adjuster in combination, the pH of cooked rice is adjusted to 5.0 to 5.4.
By adding a pH adjuster to the cooking water so that the heat resistance of the heat-resistant spore bacterium is reduced by pH fluctuation,
A method for achieving commercial sterility at a temperature lower than that of general retort sterilization (for example, at 120 ° C. for 20 minutes) is known (Japanese Patent No. 2692556). However,
Also in this method, heating at 100 ° C. or more,
By adding a pH adjuster to cooking water, the quality of cooked rice including taste and texture has been reduced.

Further, even when the same heat treatment as that of ordinary rice cooking is performed, cooked rice to which a pH adjuster (bacteriostatic agent) has been added so as to suppress the final pH of cooked rice to 4.8 or less, Since it has a sourness and an acid odor caused by the pH and the pH adjuster, it is hard to say that this is the quality of freshly cooked rice.

Therefore, the present invention relates to a method for producing cooked rice, which can be stored for a long time at room temperature, and can have the same quality as freshly cooked rice in terms of taste and texture during eating. The purpose is to provide packed rice.

[0008]

In order to achieve the above object, the present invention provides a method for producing rice that can be stored for a long period of time, comprising the steps of: washing rice washed with immersion water containing adipic acid (HOOC (CH ₂ ) ₄ COOH); Preferably, the concentration of adipic acid is 0.1.
After immersion in an adipic acid-containing immersion water of 0.5 to 1%,
It is characterized in that the dipped rice from which the dipped water has been drained is washed with water, the washed rice is filled in a container, cooked water is added, and the rice is heated.

Further, the pH of the immersion water containing adipic acid is adjusted
Adjusting with at least one of sodium, potassium or calcium adipate and alkali;
In particular, when the adipate is used, its pH is adjusted to 4
It is characterized in that it is adjusted to ８8. Further, the immersion time of rice in the adipic acid-containing immersion water is preferably at least 2 minutes or more and up to the time of normal immersion treatment, and it is also effective to use ultrasonic treatment together with this immersion. It is a target.

[0010] The water washing of the immersed rice is preferably carried out using water at 5 to 70 ° C, and in this water washing, an effective water washing treatment can be carried out by using ultrasonic treatment together. . Further, the heat treatment is preferably carried out in a usual rice cooking process under normal pressure, and cooked rice can be produced by adding ingredients and seasonings as necessary.

[0011] The packaged cooked rice of the present invention which can be stored for a long time is a cooked rice cooked by the above-mentioned method, which is sealed with a gas barrier film. In particular, the content of adipic acid is 0.07% by weight or less. Is the pH of cooked rice
Is 5 to 8.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart showing standard steps for carrying out a method for producing cooked rice which can be stored for a long time according to the present invention.

First, the first rice washing step 11 is carried out by a usual rice washing method, and a usual rice washing treatment may be carried out using ordinary water such as tap water as usual. The next immersion step 12 is a step of immersing the rice after the rice washing step 11 in immersion water containing adipic acid (adipic acid-containing immersion water). The concentration of adipic acid in the adipic acid-containing immersion water used in the immersion step 12 is not particularly limited,
If it is less than 0.05%, the effect of adding adipic acid, that is, the effect of lowering the heat resistance of heat-resistant spores may not be sufficiently obtained. Since the water washing process must be performed for a long time and consumes a large amount of water,
In the range of 0.05 to 1%, preferably 0.1 to 0.5%
Is appropriate.

The duration of the immersion step 12 depends on the concentration of adipic acid in the adipic acid-containing immersion water and the treatment temperature, but if it is less than 2 minutes, the rice is insufficiently impregnated with adipic acid and heat-resistant spores are formed. The effect of reducing the heat resistance of the bacterium may not be sufficiently obtained, and if it exceeds 120 minutes, the rice may be impregnated with adipic acid more than necessary, which may lower the taste after cooking, so that it is usually used. Is in the range of 2 to 120 minutes,
Preferably, the range is 10 to 90 minutes.

Further, the immersion water containing adipic acid may be one obtained by adding an appropriate amount of adipic acid to ordinary water such as tap water and dissolving the same. However, sodium adipate, potassium adipate and calcium adipate may be used. May be used or used in combination. The pH of the adipic acid-containing immersion water can be adjusted to an appropriate range by using adipic acid in combination with these adipates and alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide. .

The pH of the immersion water containing adipic acid depends on the concentration of adipic acid and the treatment temperature, but is preferably in the range of 4 to 8. If the pH is too low or too high, the effect of lowering the heat resistance may not be obtained, the load of the washing step may increase, or the taste of cooked rice may decrease.

The treatment temperature (water temperature) in the immersion step 12 is arbitrary, and a higher temperature is more effective.
If the temperature exceeds 70 ° C., gelatinization of the starch on the rice surface layer occurs. If the gelatinization proceeds to a certain extent, it becomes difficult to remove adipic acid in the washing step. On the other hand, when the temperature is low, for example, when the temperature is lower than 5 ° C., it takes not only a long time to obtain a predetermined effect, but also adipic acid may be precipitated due to low solubility of adipic acid in water. Therefore, the treatment temperature is suitably in the range of 5 to 70 ° C., and considering the energy for heating and cooling water, 10 to 30 ° C. which is close to the normal water temperature is optimal.

Furthermore, by using ultrasonic treatment in this immersion step 12, the adipic acid-containing immersion water can be sufficiently distributed to the details of rice, so that the effect of lowering the heat resistance of the heat-resistant spore bacterium can be obtained. It can be even higher.

After finishing the immersion step 12 as described above, the rice (immersed rice) enters a water washing step 14 through a draining step 13,
The immersion water containing adipic acid is removed from the immersed rice. The water washing step 14 is for removing adipic acid to such an extent that the effect of adipic acid does not appear on the cooked rice, and the water washing treatment itself can be performed by a conventional method. For example, immersion in ordinary water such as tap water and stirring as appropriate, immersion in running water, showering, or by alternately repeating immersion in water and draining, can be performed underwater Ultrasonic cleaning can also be used together. The temperature at this time is not particularly limited, and the higher the temperature, the higher the efficiency of adipic acid removal. However, when the temperature exceeds 70 ° C., gelatinization of starch occurs as described above, and However, if the temperature is lower than 5 ° C., it takes a long time to perform sufficient water washing, so that usually 5 to 70 ° C., preferably 10 to 30 ° C. is appropriate.

Water washing step 14 for removing adipic acid
(Washed rice) is filled in a suitable container together with a predetermined amount of cooking water in a filling step 15, and then subjected to a predetermined heating step 16, that is, a rice cooking process. The container used in the heating step 16 is optional, but in the case of manufacturing a packaged rice packed with one serving, a heat-resistant plastic tray (individual serving container) having a predetermined size may be used. In addition, ordinary tap water can be used as the cooking water, and various cooked rice can be obtained by adding appropriate ingredients and seasonings together with the cooking water.

Further, the opening of the heat-resistant plastic tray can be covered with a film having vapor permeability and bacterial barrier properties. In addition, the heating method is also optional. When the above-mentioned individual food container is used, high-temperature steam is usually used, but when rice is cooked using a metal container such as a kettle, heating is performed by direct heat. You can also.

The cooked rice cooked in the heating step 16 can be stored as an individual food container or transferred to an appropriate container, and then sealed in a sealing step 17 with a gas barrier film so that the product can be stored for a long period of time. Rice is obtained. Further, an oxygen scavenger may be enclosed in the gas barrier film as needed. Further, a packaging form such as a retort pouch can be adopted.

The packaged rice thus obtained can reduce the heat resistance of heat-resistant spores present in rice grains by the action of adipic acid in the immersion step 12 using immersion water containing adipic acid. Since a commercial sterile state can be achieved by heating in the heating step 16, long-term storage is possible, and the food can be eaten by heating in a microwave oven or the like.

At this time, the residual concentration of adipic acid in the wrapped rice is preferably 0.07% or less, particularly preferably 0.05% or less, and more preferably 0.03% or less. When the residual concentration of adipic acid is 0.0
If it is 7% or less, the difference in taste is identifiable in comparison with ordinary cooked rice, but it is substantially the same,
If it is 0.05% or less, the taste is so good that it cannot be distinguished from cooked rice in a usual manner.

The pH of the cooked rice is 5.0 to 5.0.
It should be set to be in the range of 8.0. That is, when the pH of cooked rice is less than 5 or more than 8,
Taste may be reduced and the commercial value may be impaired. Furthermore, if the pH is in the range of 5.2 to 7.8, the same taste as cooked rice cooked by a normal cooking method can be obtained.
Is in the range of 5.5 to 7.5, a good taste that is difficult to distinguish from ordinary cooked rice is obtained.

Adipic acid residual concentration and pH as described above
The range can be easily attained by appropriately setting the treatment conditions in the immersion step 12 and the water washing step 14 without losing the heat resistance reducing effect to the extent that commercial sterility can be achieved. The pH of cooked rice is a value obtained by adding 9 times the amount of distilled water to cooked rice to crush the cooked rice and measuring the pH of the supernatant.

By manufacturing packaged cooked rice that can be stored for a long period of time in this way, it is not necessary to provide expensive facilities such as a clean booth for sterilizing the production line environment, and thus it is possible to reduce equipment costs. .

[0028]

EXAMPLE 1 First, the effect of lowering the heat resistance of the heat-resistant spore bacterium was examined by performing the immersion step using immersion water containing adipic acid. To rice sharpening juice that has been pre-pressurized and heat sterilized,
Spores having extremely high heat resistance, picked from rice cereal, were suspended to obtain a bacterial solution.

Then, as shown in Table 1, the base which was not subjected to the adipic acid treatment, that is, the one subjected to the immersion treatment in water (adipic acid concentration 0%) to which no adipic acid was added (Experiment No. 1) was used. , Experiment Nos. 11 to 17, Experiment Nos. 21 to 25 and Experiment Nos. 31 to 35 were compared with those treated with adipic acid under various conditions. The adipic acid treatment is performed by adding a predetermined amount of adipic acid so that the concentration of adipic acid in the bacterial solution becomes a set value, adjusting the pH to 7.0 with an aqueous sodium hydroxide solution, and leaving the mixture at a predetermined temperature for a predetermined time. Then, 6 ml of the bacterial solution was centrifuged (first time), 5 ml of the supernatant was discarded, 5 ml of fresh sterilized sharpening juice was added and suspended, and a second centrifugation was performed. 5 ml of the supernatant was discarded, and a treatment simulating washing with water in which 5 ml of freshly sterilized sharpening juice was added and resuspended was performed, and this was used as a sample bacterial solution.

In each experiment, a fixed amount of the sample bacterial solution without adipic acid treatment and a fixed amount of the sample bacterial solution with adipic acid treatment were maintained at a temperature of 100 ° C., and the number of remaining bacteria was measured at predetermined time intervals. Draw a survival curve based on the obtained data, and calculate the D value (the time required to reduce the number of bacteria to 1/10)
Was performed. Table 1 shows the results. In this experiment, rice sharpening juice was targeted, but the effect of reducing the heat resistance of spores observed in this experiment was also observed when actual rice grains were immersed in immersion water containing adipic acid and then washed with water. Is apparently obtained. The D value is practically sufficient if the value is about 25 (minutes) or less.

[0031]

[Table 1]

Example 2 The same bacterial solution as in Example 1 was used as a sample, treated with adipic acid under the conditions shown in Table 2, and the number of surviving bacteria was examined in the same manner as in Example 1. Table 2 shows the results. From this, when the concentration of residual adipic acid during heating is the same, that is, when it is attempted to make the concentration of adipic acid remaining in cooked rice the same, when immersion water containing adipic acid containing a relatively high concentration is used. It can be seen that those treated for a short time have a greater effect of lowering the heat resistance of the spores than those treated for a long time at a low concentration.

[0033]

[Table 2]

Example 3 In order to confirm the effect of the concentration of adipic acid remaining in cooked rice on the quality of cooked rice, rice washed by a conventional method was cooked under the conditions shown in Table 3 and then cooked. The measurement of adipic acid concentration and the sensory test were performed.

It was found that the concentration of adipic acid in cooked rice was reduced by washing with water, and when the amount became 0.07% or less, cooked rice having a sufficiently good taste was obtained.

[0036]

[Table 3]

Example 4 100 kg of glutinous rice was washed and drained (removing water adhering to the surface) by a conventional method, and then a 0.3% adipic acid aqueous solution (adipic acid was dissolved in hot water to obtain a high concentration Prepare an aqueous solution of adipic acid and dilute it with water at room temperature to 0.3%
A solution with a uniform concentration. ) 1 in 30 liters
Soaked for hours. After the immersion water was drained using a colander, the immersion rice was immersed in a container filled with water so that the immersion rice was submerged, water was supplied from above, and the immersion rice was washed with stirring while overflowing. At this time, the soaked rice was transferred to a container filled with fresh water as needed, and washing was continued with water.

110 g of immersed rice, which had been thoroughly washed out of adipic acid on the rice surface and drained, was charged into a plastic molded container containing an oxygen barrier material (EVOH), and at the same time, 90 ml of activated carbon treated water was charged as cooking water. Next, the upper surface of the container was sealed with a film (primary film) partially provided with a vapor-permeable film. Then, it put into the heating device (steamer) and cooked rice at 100 degreeC for 60 minutes. After the rice was cooked, the condensed water of the vapor remaining on the film upper surface was removed, and then sealed with a film (secondary film) containing an oxygen barrier material (EVOH) to obtain packed rice.

Then, a sample of 1000 meals in which an oxygen scavenger (trade name: Ageless) was sealed in the gap between the primary film and the secondary film, and a sample of 1,000 meals in which no oxygen scavenger was sealed were prepared. After storing these in a constant temperature room at 35 ° C. for 2 weeks, the state of spoilage was examined in accordance with the sanitary test method for pressurized and heat-sterilized foods in containers and packaging, so-called retort foods.

No decay was observed in either the case where the oxygen scavenger was sealed or the case where the oxygen scavenger was not sealed. Therefore, it can be said that the packed cooked rice of the present example achieved a commercial sterility state. Furthermore, the cooked rice in which the oxygen scavenger was sealed had almost no sourness or odor, and had the same quality as freshly cooked rice. The pH of cooked rice in this example was 5.2.

On the other hand, as a control experimental group, adipic acid immersion treatment was performed in the same manner, but without the subsequent washing step, 1000 pieces of cooked cooked rice were prepared and similarly stored at 35 ° C. for 2 weeks. . The cooked rice in this control experimental plot achieved commercial sterility, but had sourness and odor, and was inferior in quality to freshly cooked rice.
In this case, the pH of the cooked rice was 4.5.

In another control experiment group, 1,000 meals of packaged cooked rice were prepared using rice simply immersed in tap water without immersion in adipic acid, and stored at 35 ° C. for 2 weeks.
As a result, there were two specimens with advanced corrosion, commercial aseptic condition was not achieved, and it was not suitable for eating.

[0043]

As described above, according to the present invention,
Since the heat resistance of microorganisms adhering to rice grains can be reduced, heat-resistant spores can be killed even under normal rice cooking conditions, that is, conditions without heating exceeding 100 ° C., and commercial sterile conditions can be achieved. And a packaged cooked rice having a taste and aroma of cooked rice having the same quality as freshly cooked rice can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one example of a process of the method of the present invention.

[Explanation of symbols]

11: rice washing process, 12: dipping process, 13: draining process,
14: washing step, 15: filling step, 16: heating step, 1
7 Sealing process

Continuation of the front page (72) Inventor Osamu Yoshida F-term within Nippon Sanso Co., Ltd. 1-16-7 Nishi-Shimbashi, Minato-ku, Tokyo 3E035 AA20 BA08 BC02 BD02 BD04 BD06 CA07 4B021 LA24 LP09 LW09 MQ05 4B023 LC08 LE11 LG01 LK04 LL01 LL05 LP03 LP05 LP10 LP18 LQ03

Claims (13)

[Claims] After immersing the washed rice in immersion water containing adipic acid, the immersion water is drained, the immersed rice is washed with water, the washed rice is filled in a container, and cooked water is added to the rice for heat treatment. A method for producing cooked rice that can be stored for a long time. 2. The method according to claim 1, wherein the adipic acid-containing immersion water has a concentration of adipic acid of 0.05 to 1%. 3. The method for producing rice which can be stored for a long time according to claim 1, wherein the pH of the adipic acid-containing immersion water is adjusted by at least one of sodium, potassium or calcium adipic acid salt and alkali. . 4. The long-term dipping water according to claim 1, wherein said adipic acid-containing immersion water is obtained by dissolving sodium, potassium or calcium adipic acid salt in water, and has a pH of 4 to 8. A method of producing storable cooked rice. 5. The method according to claim 1, wherein the immersion time of the rice in the adipic acid-containing immersion water is 2 minutes or more. 6. The method according to claim 1, wherein the rice is immersed in the adipic acid-containing immersion water together with ultrasonic treatment. 7. The method according to claim 1, wherein the washing of the soaked rice is carried out using water at a temperature of 5 to 70 ° C. 8. The method for producing cooked rice according to claim 1, wherein ultrasonic treatment is used when washing the soaked rice with water. 9. The method according to claim 1, wherein the heat treatment is a rice cooking process under normal pressure. 10. The method according to claim 1, wherein at least one of ingredients and seasonings is added together with the cooking water. 11. A packaged cooked rice, wherein cooked rice cooked by the method according to any one of claims 1 to 10 is sealed with a gas barrier film. 12. The cooked rice having an adipic acid content of 0.0
The packaged rice according to claim 11, wherein the content is 7% by weight or less. 13. The packaged cooked rice according to claim 11, wherein the pH of the cooked rice is 5 to 8.