Method for producing cooked rice

Abstract

To provide a method for producing cooked rice by which chilled cooked rice can be refrigerated for a long time so as to be edible without heating and frozen cooked rice can be refrigerated and thawed so as to be edible even without heating by suppressing aging of the chilled cooked rice and the frozen cooked rice and white waxing of the frozen cooked rice.SOLUTION: This method for producing the chilled cooked rice comprises cooking raw rice made of polished rice (S4), mixing the cooked rice just after cooking with a liquid mixture obtained by dissolving glucide in water (S5), and cooling the mixture (S6). The frozen cooked rice is obtained by dissolving glucide in water, mixing the solution with cooked rice just after cooking raw material rice composed of polished rice, cooling the mixture and rapidly freezing the cooled mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing cooked rice, and in particular to a method for producing cooked rice that can suppress aging and white wax formation. [Background technology]

[0002] Consumer needs for rice meals today are diverse, ranging from diversifying food options, individual meals, convenience, ready-to-eat meals, and food safety and security. As a result, convenience stores and supermarkets are seeing an increase in the number of ready-to-eat meals, such as bento boxes, rice balls, and frozen foods. Meanwhile, most of the rice products sold at convenience stores and supermarkets, including the frozen rice mentioned above, are produced in rice factories, which face challenges such as labor shortages and waste. For this reason, many supermarkets and convenience stores offer "chilled rice," which is delivered and sold refrigerated at a temperature of 1°C to 10°C, or "frozen rice," which is distributed and sold frozen. This extends the shelf life, reduces waste, eliminates labor shortages through centralized production, and eliminates preservatives. However, both types of rice products require heating in a microwave oven.

[0003] This is because rice starch, the main component of cooked rice, is weak at low temperatures. For example, in the case of the aforementioned "chilled cooked rice," rice starch undergoes retrogradation at temperatures as low as 1 to 10 degrees Celsius, becoming hard. When eaten, the retrograded rice starch must be restored by heating in a microwave oven. However, when cooked rice is combined with raw ingredients, such as in rice balls with raw cod roe, the ingredients are also heated by heating in a microwave oven, which reduces the product value, placing restrictions on the ingredients that can be used. Therefore, if cooked rice with reduced retrogradation could be provided even in refrigerated distribution and sales, it could be eaten without the need for heating, making it possible to meet diversifying consumer needs.

[0004] On the other hand, frozen cooked rice has the advantage of being able to extend the shelf life, but has the problem of white waxing occurring when thawed. However, since frozen cooked rice can be set to have a longer shelf life than chilled cooked rice, it would be useful if it were possible to provide cooked rice that can be eaten without heating by suppressing white waxing and aging even when frozen cooked rice is thawed from a chilled state.

[0005] In conventional methods for producing cooked rice, raw rice is cooked in the presence of α,α-trehalose, which effectively prevents deterioration in the texture and quality of cooked rice over time due to starch retrogradation, drying, etc. (Patent Document 1).

[0006] In addition, there is a method for producing cooked rice that satisfies at least one, and preferably two or more of the following: "(A) Dryness of the surface is suppressed even after a long time has passed," "(B) Staling is suppressed even after a long time has passed," "(C) Excellent loosening even after a long time has passed," and "(D) Excellent freshly cooked flavor even after a long time has passed" by adding (a) 4-α-glucanotransferase, (b) α-amylase, and (c) maltotriohydrolase before or during cooking (Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-147916 [Patent Document 2] Patent No. 7468875 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the conventional methods for producing cooked rice described above, α,α-trehalose (Patent Document 1), 4-α-glucanotransferase, and others (Patent Document 2) are added before or during cooking, which does not sufficiently suppress aging and white waxing.If the rice is chilled and refrigerated for more than 24 hours, it cannot be eaten without heating.Furthermore, if the rice is frozen and thawed, white waxing and aging occur, making it impossible to eat without heating.

[0009] Therefore, the object of the present invention is to provide a method for producing cooked rice that can extend the refrigeration time for chilled cooked rice so that it can be eaten without heating by suppressing the aging of chilled cooked rice and frozen cooked rice and the white waxiness of frozen cooked rice, and that can also provide frozen cooked rice so that it can be eaten without heating by thawing it in the refrigerator. [Means for solving the problem]

[0010] The present invention was created to solve the above-mentioned problems, and firstly, is a method for producing cooked rice that can be stored in a refrigerated state and eaten without heating, characterized by comprising the following steps: a rice washing step in which raw material rice made from polished rice is washed; a soaking step in which the washed raw material rice is soaked in water; a rice cooking step in which the soaked raw material rice is cooked to produce cooked rice; a post-mixing step in which a post-mixing liquid made by dissolving carbohydrates in water is mixed into the cooked rice immediately after cooking; and a cooling step in which the cooked rice with the post-mixing liquid mixed in is cooled to 1°C to 10°C.

[0011] In the first configuration of the method for producing cooked rice, in the post-mixing step, carbohydrates are dissolved in water and the post-mixing liquid is mixed into the cooked rice immediately after cooking. The carbohydrates and water in the post-mixing liquid improve the water retention of the surface layer of the rice, preventing aging, and the rice can be eaten without heating even if it has been refrigerated for 24 hours or more.

[0012] Secondly, there is a method for producing cooked rice that can be stored in a frozen state and thawed in the refrigerator before consumption so that it can be eaten without heating, and is characterized by having the following steps: a rice washing step in which raw material rice made from polished rice is washed; a soaking step in which the washed raw material rice is soaked in water; a rice cooking step in which the soaked raw material rice is cooked to produce cooked rice; a post-mixing step in which a post-mixing liquid obtained by dissolving carbohydrates in water is mixed into the cooked rice immediately after cooking; and a freezing step in which the cooked rice with the post-mixing liquid mixed in is quickly frozen.

[0013] In the second configuration of the cooked rice manufacturing method, in the post-mixing liquid mixing step, carbohydrates are dissolved in water and the post-mixing liquid is mixed into the cooked rice immediately after cooking. The carbohydrates and water in the post-mixing liquid improve the water retention of the surface layer of the rice, preventing aging and preventing white waxing. By thawing the frozen cooked rice in the refrigerator, it can be eaten without heating.

[0014] Thirdly, in the first or second configuration, the rice is cooked in a state where water in which carbohydrates are dissolved is added to the raw material rice.

[0015] In the third configuration, by using cooking water in which carbohydrates have been dissolved during the rice cooking process, the carbohydrates enter the rice grains during cooking, improving the water retention capacity inside the rice grains, thereby further suppressing aging and white wax formation.

[0016] Fourthly, in the first or second configuration, the carbohydrate dissolved in the post-mixing liquid is any one of the materials in the material group consisting of materials belonging to disaccharides, materials belonging to trisaccharides, materials belonging to tetrasaccharides, and materials belonging to sugar alcohols, or any combination of materials in the material group. Therefore, even if carbohydrates are mixed, the sweetness of the cooked rice does not become stronger, and the taste of the cooked rice is not affected.

[0017] Fifthly, in the first or second configuration, the carbohydrate dissolved in the post-mixing liquid is any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof. Therefore, even if carbohydrates are mixed, the sweetness of the cooked rice does not become stronger, and the taste of the cooked rice is not affected.

[0018] Sixth, in the third configuration, the carbohydrate dissolved in the rice cooking water is any one of the materials in the group consisting of disaccharides, trisaccharides, tetrasaccharides, and sugar alcohols, or any combination of materials in the group. Therefore, even if carbohydrates are added, the sweetness of the cooked rice does not become stronger, and the taste of the cooked rice is not affected.

[0019] Seventh, in the third aspect, the carbohydrate dissolved in the rice cooking water is any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof. Therefore, even if carbohydrates are mixed, the sweetness of the cooked rice does not become stronger, and the taste of the cooked rice is not affected. [Effects of the Invention]

[0020] In the method for producing cooked rice according to claim 1 of the present invention, in the step of mixing the post-mixing liquid, carbohydrates are dissolved in water and the post-mixing liquid is mixed into the cooked rice immediately after cooking. The carbohydrates and water in the post-mixing liquid improve the water retention of the surface layer of the rice, preventing aging, and the rice can be eaten without heating even if it has been refrigerated for 24 hours or more.

[0021] Furthermore, in the method for producing cooked rice of claim 2, in the post-mixing step, carbohydrates are dissolved in water and the post-mixing liquid is mixed into the cooked rice immediately after cooking. The carbohydrates and water in the post-mixing liquid improve the water retention of the surface layer of the rice, preventing aging and preventing white wax from forming. By thawing the frozen cooked rice in the refrigerator, it can be eaten without heating. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a flowchart showing a method for producing chilled cooked rice. [Figure 2] 1 is a flowchart showing a method for producing frozen cooked rice. DETAILED DESCRIPTION OF THE INVENTION

[0023] In the present invention, the object of providing a method for producing cooked rice that can extend the refrigeration period for chilled cooked rice so that it can be eaten without heating by suppressing the aging of chilled cooked rice and frozen cooked rice and the white waxiness of frozen cooked rice is achieved as follows.

[0024] The manufacturing process for chilled cooked rice is as shown in Figure 1, and the manufacturing process for frozen cooked rice (which may also be frozen chilled cooked rice) is as shown in Figure 2. Steps S1 to S7 are common to both Figure 1 and Figure 2, so steps S1 to S7 will be explained first, and then the remaining steps for frozen cooked rice will be explained.

[0025] Chilled cooked rice is stored in a chilled state, while frozen cooked rice is stored in a frozen state and thawed in a chilled state before eating.

[0026] Brown rice is polished to obtain polished rice (S1 (Fig. 1 and Fig. 2)), and the polished rice obtained is washed (S2 (Fig. 1 and Fig. 2), rice washing process). The type of polished rice is assumed to be non-glutinous rice, including low-amylose rice.

[0027] Next, the washed polished rice is soaked in water (soaking water) (S3 (Figures 1 and 2), soaking process). Generally, to cook rice, polished rice is washed and soaked until it absorbs water up to about 34%.

[0028] Next, the soaked rice is cooked (S4 (Figures 1 and 2), rice cooking step), in which cooking water is added so that the weight of the cooked rice is about 2.2 times that of the polished rice, and the rice is heated for about 20 minutes in a rice cooker or the like, and then steamed for about 20 minutes. Note that the cooking method is not particularly limited; it may also be a cooking method known as steam cooking, in which washed and soaked rice is heated in steam while being sprayed with water, thereby absorbing water and heating at the same time.

[0029] There are no particular restrictions on the soaking water and cooking water used for cooking rice, but the amount of cooking water used tends to be greater as the amount of water added increases, which tends to be more effective in preventing aging during refrigerated storage, but has the disadvantage of making the taste softer. On the other hand, with regard to the white waxiness that occurs when frozen cooked rice is thawed, if the amount of cooking water is large, it is affected by moisture expansion during freezing, but white waxiness can be suppressed by the water retention properties of the post-mixing liquid of the present invention. In other words, the effect of post-mixing liquid in suppressing white waxiness is greater than the effect of moisture expansion during freezing. The effect of moisture expansion during freezing can be reduced by quick freezing.

[0030] For chilled cooked rice, it is preferable to add cooking water so that the weight immediately after cooking is about 2.1 to 2.5 times the weight of the raw rice, and for frozen cooked rice that is thawed in the refrigerator, it is preferable to add cooking water so that the weight is about 1.8 to 2.2 times the weight of the raw rice.

[0031] Next, an aqueous solution of carbohydrates dissolved in water is mixed as a post-mixing liquid into the cooked rice cooked as described above immediately after cooking (S5 (FIGS. 1 and 2), post-mixing liquid mixing step). In other words, the post-mixing liquid is poured onto the cooked rice while it is still at a high temperature (for example, 65°C to 80°C) immediately after cooking, without cooling the cooked rice. In other words, even if the post-mixing liquid is mixed after the cooked rice has cooled, the sugars will not penetrate into the surface layer of the rice, so the post-mixing liquid is mixed immediately after cooking. Specifically, after the post-mixing liquid has been mixed into the cooked rice, the cooked rice is stirred to mix the post-mixing liquid evenly into the cooked rice.

[0032] The carbohydrates include sugars, such as monosaccharides and disaccharides, and sugars other than sugars such as sugar alcohols and polysaccharides. These carbohydrates improve the water retention capacity of the surface layer of rice and inhibit aging and white wax formation.

[0033] Generally, as the molecular weight decreases, the sugars penetrate between the rice starch molecules, improving the water retention of the rice starch on the surface and inside of the rice, and thereby preventing the rice starch from retrograding and becoming white waxy. However, as the molecular weight decreases, the sugars become sweeter. Therefore, suitable sugars that can improve the water retention while minimizing the effect on the taste of cooked rice include disaccharides (e.g., trehalose, maltose, isomaltose), trisaccharides (e.g., maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose), tetrasaccharides (e.g., stachyose, maltosyltrehalose), and sugar alcohols (e.g., reduced starch syrup). It is preferable to dissolve these, either alone or in any combination, in water at a concentration of 10 to 40% to prepare a mixed liquid. That is, any material from a material group consisting of materials belonging to disaccharides (e.g., trehalose, maltose, isomaltose), materials belonging to trisaccharides (e.g., maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose), materials belonging to tetrasaccharides (e.g., stachyose, maltosyltrehalose), and materials belonging to sugar alcohols (e.g., reduced starch syrup) or any combination of materials from the material group is dissolved in water to form a mixture. In other words, if the materials belonging to the disaccharides are trehalose, maltose, and isomaltose, the materials belonging to the trisaccharides are maltotriose, isomaltotriose, raffinose, panose, and glucosylsucrose, the materials belonging to the tetrasaccharides are stachyose and maltosyltrehalose, and the material belonging to the sugar alcohols is reduced starch syrup, the material group will consist of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, and reduced starch syrup, and the carbohydrate used in the subsequent mixture will be any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, and reduced starch syrup, or any combination thereof.

[0034] In addition to the above materials, starch syrup may also be used, and the carbohydrate to be subsequently dissolved in the mixed liquid may be any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof.

[0035] Furthermore, it is preferable to add cooking water so that the weight of the final cooked rice after adding the mixed liquid and cooling is about 1.9 to 2.5 times the weight of the raw rice immediately after cooking, for both chilled and frozen cooked rice. Furthermore, it is preferable that the weight of the final cooked rice after adding the carbohydrates, mixing the mixed liquid, and cooling is about 2.3 to 2.9 times the weight of the raw rice.

[0036] Specifically, in the case of "chilled cooked rice," 450 g of raw rice is soaked, and 580 g of soaked rice and 510 g of water are placed in a regular rice cooker and cooked to obtain approximately 1,040 g of cooked rice (approximately 2.3 times the weight of the raw rice) (note that the weight decreases due to evaporation of water during cooking). After cooking, for example, 40 g of trehalose is dissolved in 120 g of water, and this mixture is mixed with the cooked rice.

[0037] Next, the cooked rice mixed with the post-mixing liquid is cooled (S6 (FIGS. 1 and 2), cooling step) so that the weight after cooling is approximately 1190 g (taking into account the evaporation of water due to cooling). Note that in this cooling step, the cooked rice is cooled to 1°C to 10°C.

[0038] The amount of water that evaporates during cooling varies depending on the cooling method, such as leaving the rice in a refrigerator at temperatures below 10°C, cooling the rice by directly applying cold air below 10°C, or cooling by vacuum cooling. Therefore, it is necessary to adjust the amount of cooking water used when cooking raw rice depending on the cooling method.

[0039] For example, when the rice is cooled by leaving it to stand in a refrigerator after adding the post-mixing liquid, the cooked rice to which the post-mixing liquid has been added is cooled by heat exchange due to the temperature difference in the cold air inside the refrigerator, so the weight change is only about 1% of the total weight.However, when cooling by vacuum cooling, for example, the object is placed in a vacuum and cooled by the heat of vaporization, so more water evaporates than when cooling by heat exchange. For example, if 580g of soaked rice is cooked by adding 510g of cooking water to 450g of raw rice, and then 40g of trehalose is dissolved in 120g of water and mixed with the liquid, and the resulting 1200g of cooked rice is cooled using vacuum cooling to below 10°C, approximately 6% of the water will evaporate (the product temperature of the cooked rice after adding the liquid is approximately 70°C, and cooling to below 10°C requires a cooling of 60°C, but vacuum cooling generally evaporates 1% of the weight for every 10°C of cooling), and the final weight of the cooled cooked rice will be 1128g (equivalent to 1200g - 6% of the weight). Therefore, to obtain the same weight as with static cooling, approximately 585g of cooking water must be added, rather than the 510g used during cooking.

[0040] The evaporation of water during cooking is similar to the evaporation of water during cooling, and the amount of water evaporated during cooking varies depending on the rice cooking equipment and the amount of rice cooked, so adjustment of the cooking water is necessary.

[0041] Next, the cooled cooked rice is weighed and shaped (S7 (FIGS. 1 and 2)). In the case of chilled cooked rice, the cooked rice weighed and shaped in step S7 becomes chilled cooked rice.

[0042] Furthermore, in the case of frozen cooked rice, the cooked rice that has been measured and shaped is quickly frozen (S8 (Fig. 2), freezing step) and then stored frozen (S9 (Fig. 2)). This frozen and stored cooked rice becomes frozen cooked rice.

[0043] It should be noted that the cooling step (S6) may be omitted in Fig. 2. In other words, the cooked rice to which the post-mixing liquid has been mixed may be quickly frozen to produce frozen cooked rice.

[0044] The chilled cooked rice produced as described above is refrigerated, i.e., stored at a temperature of 1°C to 10°C, and can be eaten without heating. In this chilled cooked rice, mixing an aqueous solution of dissolved carbohydrates into cooked rice improves the water retention capacity of the surface layer of the rice, thereby preventing rice from aging and making the rice suitable for consumption without impairing texture, such as elasticity, even without heating. Furthermore, by adding post-mixing liquid to cooked rice, not only the water originally contained in the cooked rice but also the water in the post-mixing liquid is added, increasing the moisture content of the surface layer of the rice compared to when only carbohydrates are added, and improving the water retention capacity of the surface layer of the rice due to the carbohydrates. If only carbohydrates were mixed with cooked rice instead of post-mixing liquid, there would be insufficient water to be retained by the carbohydrates, and aging could not be prevented. In other words, the water retention capacity of the surface layer of the rice is improved by the carbohydrates and water in the post-mixing liquid.

[0045] Furthermore, since the frozen cooked rice produced as described above is stored frozen, it is thawed in a chilled state, i.e., refrigerated and thawed at a temperature of 1°C to 10°C, and eaten in the thawed state without heating. In this frozen cooked rice, by mixing an aqueous solution of dissolved carbohydrates into cooked rice, the water retention capacity of the surface layer of the rice is improved, thereby suppressing white waxiness. That is, although white waxiness usually occurs when frozen cooked rice is thawed, the water retention capacity of the surface layer of the rice after thawing is improved, so white waxiness can be suppressed. Furthermore, even in a chilled state (1°C to 10°C), the water retention capacity of the surface layer of the rice is improved, so aging can be suppressed. As a result, even when refrigerated and thawed cooked rice is eaten without heating, it is suitable for eating without losing texture such as elasticity. In this case, too, by adding post-mixing liquid to cooked rice, not only the water originally contained in the cooked rice but also the water in the post-mixing liquid is added, so the moisture content in the surface layer of the rice increases compared to when only carbohydrates are added, and the water retention capacity of the surface layer of the rice due to the carbohydrates can be improved. If only carbohydrates are mixed with cooked rice instead of post-mixing liquid, there will not be enough water to be retained by the carbohydrates, so aging and white waxiness cannot be suppressed. In other words, the carbohydrates and water in the post-mixing liquid improve the water retention capacity of the surface layer of the rice.

[0046] Furthermore, by dissolving carbohydrates not only in the post-mixing liquid but also in the cooking water, the carbohydrates enter the rice grains during cooking, improving the water retention capacity inside the rice grains, thereby further suppressing aging and white wax formation.

[0047] The carbohydrates dissolved in the rice cooking water are similar to those described above and include sugars, such as monosaccharides and disaccharides, and sugars other than sugars include sugar alcohols and polysaccharides. Carbohydrates that can improve water retention while minimizing the effect on the taste of cooked rice include disaccharides (e.g., trehalose, maltose, isomaltose), trisaccharides (e.g., maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose), and tetrasaccharides (e.g., stachyose, maltosyltrehalose). Suitable sugars include disaccharides (e.g., trehalose, maltose, isomaltose), trisaccharides (e.g., maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose), tetrasaccharides (e.g., stachyose, maltosyltrehalose), and sugar alcohols (e.g., reduced starch syrup). Any material from the group consisting of disaccharides (e.g., trehalose, maltose, isomaltose), trisaccharides (e.g., maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose), tetrasaccharides (e.g., stachyose, maltosyltrehalose), and sugar alcohols (e.g., reduced starch syrup) or any combination of materials from the group is dissolved in the rice cooking water. In other words, the carbohydrates dissolved in the rice cooking water are any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, and reduced starch syrup, or any combination thereof.

[0048] In addition to the above materials, starch syrup may also be used, and the carbohydrate dissolved in the rice cooking water may be any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof.

[0049] The present invention will be described in more detail below based on examples. First, examples of chilled cooked rice will be described using Table 1. In the following description, Koshihikari rice produced in Toyama Prefecture was used as polished non-glutinous rice, and trehalose (specifically, trehalose manufactured by Nagase Vita Co., Ltd.) was used as the carbohydrate.

[0050] [Table 1]

[0051] Examples 1 to 3 and Comparative Examples 1 and 2 in Table 1 will be explained.

[0052] In Example 1, 450 g of polished non-glutinous rice was washed and drained. Next, the rice was left in 200% water relative to its weight for 90 minutes, then removed and drained, yielding 580 g of soaked rice. The soaked rice and 510 g of cooking water were placed in a household rice cooker and cooked using a standard rice cooking method, yielding 1,040 g of cooked rice. Immediately after cooking, 40 g of trehalose was dissolved in 120 g of water, and the mixture was mixed evenly. The rice was then cooled to 10°C in a refrigerator wrapped in plastic wrap and allowed to stand at 5°C to 10°C, yielding 1,190 g of cooked rice (note that the weight was reduced by 10 g due to slight cooling and water evaporation before wrapping). 120 g of this cooked rice was removed, placed in a cold-resistant, airtight container, and stored in a refrigerator at 5°C for 24 to 48 hours before being subjected to sensory evaluation.

[0053] In Example 1, aging was improved, and the product stored for 24 hours was suitable for eating, but the product stored for 48 hours was not suitable for eating.

[0054] Example 2 was substantially the same as Example 1, except that the amount of water in the post-mixing liquid was 170 g. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1240 g.

[0055] In Example 2, aging was significantly improved compared to Example 1, and the product stored for 24 hours was suitable for eating, but the product stored for 48 hours was edible but not satisfactory.

[0056] Example 3 was similar to Example 1, except that the amount of trehalose in the post-mixing liquid was 60 g. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1210 g.

[0057] In Example 3, as in Example 1, aging was improved, and the product stored for 24 hours was suitable for eating, but the product stored for 48 hours was not suitable for eating.

[0058] Comparative examples for Examples 1 to 3 are as follows.

[0059] In Comparative Example 1, 450 g of polished non-glutinous rice was washed and drained. Next, the rice was left in 200% water relative to its weight for 90 minutes, then removed and drained, yielding 580 g of soaked rice. The soaked rice and 510 g of cooking water were placed in a household rice cooker and cooked using a standard rice cooking method, yielding 1,040 g of cooked rice. This cooked rice was then left to cool in a refrigerator at 5-10°C while wrapped in plastic wrap, yielding 1,030 g of cooked rice cooled to 10°C. 120 g of this cooked rice was removed, placed in a cold-resistant, airtight container, and stored in a refrigerator at 5°C for 24-48 hours before being subjected to sensory evaluation.

[0060] In Comparative Example 1, aging was severe, and both the product stored for 24 hours and the product stored for 48 hours were unsuitable for eating.

[0061] Comparative Example 2 was almost the same as Comparative Example 1, except that the amount of cooking water was 630 g, which was the same as the total weight of the cooking water and post-mixing water in Examples 1, 3, and 4. The cooked rice cooled to 10°C weighed 1,150 g.

[0062] In Comparative Example 2, aging was also severe, and both the products stored for 24 hours and 48 hours were unsuitable for eating.

[0063] As described above, when comparing Examples 1 to 3 with Comparative Examples 1 and 2, in Examples 1 to 3, by adding post-mixing liquid, the products stored for 24 hours became suitable for consumption, and a greater effect was obtained than in the Comparative Examples.

[0064] Next, Example 4 and Comparative Examples 3 and 4 in Table 1 will be described.

[0065] Example 4 was substantially the same as Example 1, except that the amount of cooking water was 560 g. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1240 g.

[0066] In Example 4, as in Examples 1 and 3, aging was improved, and the product stored for 24 hours was suitable for eating, but the product stored for 48 hours was not suitable for eating.

[0067] The comparative example for Example 4 was as follows.

[0068] In Comparative Example 3, the cooking water was 560 g of water mixed with 40 g of trehalose, as compared to Comparative Example 1. In other words, compared to Example 5, the carbohydrate was added before cooking rather than after cooking. The cooked rice cooled to 10°C weighed 1,120 g.

[0069] In Comparative Example 3, aging was improved compared to Comparative Examples 1 and 2, but the product stored for 24 hours was edible but not sufficient, and the product stored for 48 hours was not suitable for eating.

[0070] Comparative Example 4 was almost the same as Comparative Example 3, except that the amount of water in the rice cooking water was 680 g, which was the same as the total weight of the rice cooking water and post-mixing water in Example 4. The cooked rice cooled to 10°C weighed 1240 g.

[0071] In this Comparative Example 4, aging was improved in both the samples stored for 24 hours and 48 hours compared to Comparative Examples 1 to 3, but because the amount of water used in the cooking water was too high, the cooked rice became clumpy and was not suitable for eating.

[0072] As described above, when comparing Example 4 with Comparative Examples 3 and 4, adding carbohydrates to the post-mixing liquid rather than adding carbohydrates and enzymes to the cooking water resulted in rice that was suitable for eating after 24 hours of storage, and a greater effect was obtained than in the Comparative Examples.

[0073] As shown in Comparative Example 4, staling itself can be suppressed by increasing the amount of water added to the cooking water and adding sugar to the cooking water, but increasing the amount of water causes the cooked rice to become dumpling-like, which is a limiting factor. However, by adding a post-mixing liquid containing added sugar to the cooked rice as in Example 4, the cooked rice could be eaten without becoming dumpling-like, even though the total weight of the water used was the same as in Comparative Example 4. This is because if the amount of cooking water is excessively large, the rice grains absorb too much water and become dumpling-like. In other words, it can be said that staling is suppressed not only by the sugar in the post-mixing liquid but also by the water in the post-mixing liquid.

[0074] Next, Example 5 and Comparative Example 5 in Table 1 will be described.

[0075] Example 5 was similar to Example 1, except that 40 g of trehalose was mixed not only with the post-mixing liquid but also with the rice-cooking water. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1230 g.

[0076] In Example 5, aging was significantly improved compared to Example 1, and the product stored for 24 hours was suitable for eating, but the product stored for 48 hours was edible but not satisfactory.

[0077] The comparative example for Example 5 was as follows.

[0078] In Comparative Example 5, the addition of the post-mixing liquid was omitted compared to Example 5. In other words, compared to Comparative Example 3, the amount of post-mixing liquid was 510 g compared to 560 g of rice cooking water. The cooked rice cooled to 10°C weighed 1070 g.

[0079] In Comparative Example 5, aging was improved compared to Comparative Examples 1 and 2, but the product stored for 24 hours was edible but not sufficient, and the product stored for 48 hours was not suitable for eating.

[0080] As described above, a comparison of Example 5 and Comparative Example 5 revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting aging than mixing carbohydrates into the rice cooking water alone. Furthermore, a comparison of Example 5 with Examples 1 to 3 revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting aging than mixing carbohydrates into the post-mixing liquid alone.

[0081] Next, examples of frozen cooked rice will be explained using Table 2. In the following explanation, except for Example 17 and Comparative Example 15, Koshihikari rice produced in Toyama Prefecture was used as the polished rice, and trehalose (specifically, trehalose manufactured by Nagase Vita Co., Ltd.) was used as the carbohydrate.

[0082] [Table 2]

[0083] Examples 6 to 8 and Comparative Examples 6 and 7 in Table 2 will be explained.

[0084] In Example 6, 450 g of polished non-glutinous rice was washed and drained. Next, the rice was left in 200% water relative to its weight for 90 minutes, then removed and drained, yielding 580 g of soaked rice. The soaked rice and 510 g of cooking water were placed in a household rice cooker and cooked using a standard rice cooking method, yielding 1,040 g of cooked rice. Immediately after cooking, 40 g of trehalose was dissolved in 120 g of water, and the resulting mixture was mixed uniformly. The mixture was then left to cool in a refrigerator at 5°C to 10°C, wrapped in plastic wrap, and cooled to 10°C, yielding 1,190 g of cooked rice. 120 g of this cooked rice was removed and placed in a cold-resistant, airtight container, and the container containing the cooked rice was stored at -40°C for 90 minutes and flash-frozen. The flash-frozen cooked rice was first stored in a freezer at -25°C for 24 hours to stabilize the temperature, then transferred to a refrigerator at 5°C to thaw. Sensory evaluation was conducted 24 and 48 hours after thawing began.

[0085] In Example 6, some improvement in white waxiness and aging was observed, and the product left for 24 hours was edible, although not sufficient, while the product left for 48 hours was not suitable for consumption.

[0086] Example 7 was similar to Example 6, except that the post-mixing liquid was 170 g of water to which 40 g of trehalose had been dissolved. The cooked rice weighed 1,240 g when cooled to 10°C.

[0087] In Example 7, white waxing and aging were improved more than in Example 6, and the product after 24 hours was suitable for eating, but the product after 48 hours was not suitable for eating.

[0088] Example 8 was substantially the same as Example 6, except that the amount of trehalose added to the post-mixing liquid was 60 g. The cooked rice weighed 1,210 g when cooled to 10°C.

[0089] In Example 8, white waxing and aging were improved more than in Example 6, and the product left for 24 hours was still edible, although not completely edible, while the product left for 48 hours was not suitable for consumption.

[0090] Comparative examples for Examples 6 to 8 are as follows.

[0091] In Comparative Example 6, 450 g of polished non-glutinous rice was washed and drained. Next, the rice was left in 200% water relative to its weight for 90 minutes, then removed and drained, yielding 580 g of soaked rice. The soaked rice and 510 g of cooking water were placed in a household rice cooker and cooked using a standard rice cooking method, yielding 1040 g of cooked rice. This cooked rice was then cooled to 10°C by standing in a refrigerator at 5°C to 10°C while wrapped in plastic, yielding 1030 g of cooked rice. 120 g of this cooked rice was removed and placed in a cold-resistant, airtight container, and the container containing the cooked rice was stored at -40°C for 90 minutes before being flash-frozen. The flash-frozen cooked rice was then stored in a -25°C freezer for 24 hours to stabilize the temperature, and then transferred to a 5°C refrigerator for thawing. Sensory evaluation was performed 24 and 48 hours after the start of thawing.

[0092] In Comparative Example 6, white waxing and aging were severe, and the product was not suitable for eating even after 24 hours.

[0093] Comparative Example 7 was similar to Comparative Example 6, but the amount of cooking water was 630 g, which was the same as the total weight of the cooking water and post-mixing water in Examples 6 and 8. The cooked rice cooled to 10°C weighed 1,150 g.

[0094] In Comparative Example 7, white waxing and aging were also severe, and the product was not suitable for consumption even after 24 hours.

[0095] As described above, when Examples 6 to 8 are compared with Comparative Examples 6 and 7, in Examples 6 to 8, by adding the post-mixing liquid, the products stored for 24 hours were edible, although not completely, and a greater effect was obtained than in the Comparative Examples.

[0096] Next, Example 9 and Comparative Examples 8 and 9 in Table 2 will be described.

[0097] Example 9 was substantially the same as Example 6, except that the amount of cooking water was 560 g. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1240 g.

[0098] In Example 9, as in Examples 6 and 8, improvements in white waxiness and aging were observed, and the product left for 24 hours was edible, although not sufficient, while the product left for 48 hours was not suitable for consumption.

[0099] In Comparative Example 8, the cooking water was 560 g of water mixed with 40 g of trehalose. In other words, compared to Example 9, the carbohydrate was added before cooking rather than after cooking. The cooked rice cooled to 10°C weighed 1,120 g.

[0100] In Comparative Example 8, white waxing and aging were severe, and the product was not suitable for eating even after 24 hours.

[0101] Comparative Example 9 was almost the same as Comparative Example 8, except that the amount of water in the rice cooking water was 680 g, which was the same as the total weight of the rice cooking water and post-mixing water in Example 9. The cooked rice cooled to 10°C weighed 1240 g.

[0102] In Comparative Example 9, the rice stored for 24 hours showed improvement in white waxing and aging compared to Comparative Example 8, but because the amount of water used in the cooking water was too high, the cooked rice became clumpy and was therefore unsuitable for eating.

[0103] As described above, when comparing Example 9 with Comparative Examples 8 and 9, mixing carbohydrates into the post-mixing liquid rather than mixing them into the cooking water resulted in edible products stored for 24 hours, and a greater effect was obtained than in the Comparative Examples.

[0104] Next, Example 10 and Comparative Example 10 in Table 2 will be described.

[0105] Example 10 was similar to Example 6, except that 40 g of trehalose was mixed not only with the post-mixing liquid but also with the rice-cooking water. The cooked rice cooled to 10°C after mixing with the post-mixing liquid weighed 1230 g.

[0106] In Example 10, the white waxing and aging were significantly improved compared to Example 6, and also compared to Example 9. The product left for 24 hours was still edible, although it was inferior to Example 7 and not sufficient, while the product left for 48 hours was not suitable for eating.

[0107] The comparative example for Example 10 was as follows.

[0108] In Comparative Example 10, the addition of the post-mixing liquid was omitted compared to Example 10. In other words, compared to Comparative Example 8, the amount of post-mixing liquid was 510 g compared to 560 g of rice cooking water. The cooked rice cooled to 10°C weighed 1070 g.

[0109] In Comparative Example 10, white waxing and aging were improved more than in Comparative Example 6, but both the samples stored for 24 hours and 48 hours were unsuitable for eating.

[0110] As described above, when Example 10 is compared with Comparative Example 10, it is found that mixing carbohydrates into the rice cooking water and into the post-mixing liquid is more effective in inhibiting white waxing and aging than mixing carbohydrates into the rice cooking water alone. Furthermore, when Example 10 is compared with Example 6, it is found that mixing carbohydrates into the rice cooking water and into the post-mixing liquid is more effective in inhibiting aging than mixing carbohydrates into the post-mixing liquid alone.

[0111] In the above explanation, an example was described in which trehalose was used as the carbohydrate, but similar results were obtained when other carbohydrates were used.

[0112] That is, in Examples 1 to 5 and Comparative Examples 1 to 5, even when chilled cooked rice was tested using maltose, which is the same disaccharide as trehalose, instead of trehalose, the results were similar to those obtained when trehalose was used.

[0113] That is, when Examples 1 to 3 and Comparative Examples 1 and 2 were compared, when maltose was used instead of trehalose in Examples 1 to 3, the addition of post-mixing liquid in Examples 1 to 3 made the product suitable for consumption after 24 hours of storage, and a greater effect was obtained than in the Comparative Examples.

[0114] Furthermore, when Example 4 and Comparative Examples 3 and 4 were compared, when maltose was used instead of trehalose, adding carbohydrates to the post-mixing liquid rather than adding carbohydrates or enzymes to the cooking water made the product more suitable for eating after 24 hours of storage, and a greater effect was obtained than in the Comparative Examples.

[0115] In addition, when maltose was used instead of trehalose in Example 5 and Comparative Example 5, a comparison of Example 5 and Comparative Example 5 revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting aging than mixing carbohydrates into the rice cooking water alone. Furthermore, a comparison of Example 5 with Examples 1 to 3 (Examples 1 to 3 using maltose) revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting aging than mixing carbohydrates into the post-mixing liquid alone.

[0116] Furthermore, in the case of frozen cooked rice, in Examples 6 to 10 and Comparative Examples 6 to 10, even when maltose was used instead of trehalose, the results were similar to those obtained when trehalose was used.

[0117] That is, when Examples 6 to 8 and Comparative Examples 6 and 7 were compared, when maltose was used instead of trehalose in Examples 6 to 8, the addition of post-mixing liquid made it possible to eat the products stored for 24 hours, although not completely, and a greater effect was obtained than in the Comparative Examples.

[0118] Furthermore, when maltose was used instead of trehalose in Example 9 and Comparative Examples 8 and 9, a comparison of Example 9 and Comparative Examples 8 and 9 showed that adding carbohydrates to the post-mixing liquid rather than adding carbohydrates to the cooking water made the product edible after 24 hours of storage, resulting in a greater effect than in the Comparative Examples.

[0119] In addition, when maltose was used instead of trehalose in Example 10 and Comparative Example 10, a comparison of Example 10 and Comparative Example 10 revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting white waxing and aging than mixing carbohydrates only into the rice cooking water. Furthermore, a comparison of Example 10 with Example 6 (Example 6 using maltose) revealed that mixing carbohydrates into the rice cooking water and the post-mixing liquid was more effective in inhibiting aging than mixing carbohydrates only into the post-mixing liquid.

[0120] Furthermore, when the carbohydrate was the disaccharide isomaltose (isomaltose is an isomer of maltose), the results were similar to those for trehalose when isomaltose was used instead of trehalose in Examples 1 to 5 and Comparative Examples 1 to 5 for chilled cooked rice.Furthermore, the results were similar to those for trehalose when isomaltose was used instead of trehalose in Examples 6 to 10 and Comparative Examples 6 to 10 for frozen cooked rice.

[0121] Furthermore, when the carbohydrate was a trisaccharide such as maltotriose, isomaltotriose, raffinose, panose, or glucosylsucrose (hereinafter referred to as "maltotriose, etc."), the results for chilled cooked rice were similar to those for trehalose even when maltotriose, etc. was used instead of trehalose in Examples 1 to 5 and Comparative Examples 1 to 5. Furthermore, the results for frozen cooked rice were similar to those for trehalose even when maltotriose, etc. was used instead of trehalose in Examples 6 to 10 and Comparative Examples 6 to 10.

[0122] Furthermore, when the carbohydrate was a tetrasaccharide such as stachyose or maltosyltrehalose (hereinafter referred to as "stachyose, etc."), the results for chilled cooked rice were the same as those for trehalose even when stachyose, etc. was used instead of trehalose in Examples 1 to 5 and Comparative Examples 1 to 5.Furthermore, the results for frozen cooked rice were the same as those for trehalose even when stachyose, etc. was used instead of trehalose in Examples 6 to 10 and Comparative Examples 6 to 10.

[0123] Furthermore, when reduced starch syrup was used as the carbohydrate, the results for chilled cooked rice were the same as those for trehalose even when reduced starch syrup was used instead of trehalose in Examples 1 to 5 and Comparative Examples 1 to 5.Furthermore, the results for frozen cooked rice were the same as those for trehalose even when reduced starch syrup was used instead of trehalose in Examples 6 to 10 and Comparative Examples 6 to 10.

[0124] Furthermore, when starch syrup was used as the carbohydrate, the results for chilled cooked rice were the same as those for trehalose even when starch syrup was used instead of trehalose in Examples 1 to 5 and Comparative Examples 1 to 5.Furthermore, the results for frozen cooked rice were the same as those for trehalose even when starch syrup was used instead of trehalose in Examples 6 to 10 and Comparative Examples 6 to 10.

Claims

1. A method for producing cooked rice that can be stored in a refrigerated state and eaten without heating, A rice washing process in which raw rice made from polished rice is washed; a soaking process in which the washed raw rice is soaked in water; a cooking step of cooking the soaked raw rice to produce cooked rice; A post-cooking liquid mixing process in which carbohydrates are dissolved in water and then mixed with the cooked rice immediately after cooking; A cooling step of cooling the cooked rice mixed with the post-mixing liquid to 1°C to 10°C; A method for producing cooked rice, comprising the steps of:

2. A method for producing cooked rice that can be stored in a frozen state and refrigerated and thawed before eating and eaten without heating, A rice washing process in which raw rice made from polished rice is washed; a soaking process in which the washed raw rice is soaked in water; a cooking step of cooking the soaked raw rice to produce cooked rice; A post-cooking liquid mixing process in which carbohydrates are dissolved in water and then mixed with the cooked rice immediately after cooking; a freezing step of rapidly freezing the cooked rice to which the post-mixing liquid has been mixed; A method for producing cooked rice, comprising the steps of:

3. 3. The method for producing cooked rice according to claim 1 or 2, wherein in the rice cooking step, the raw material rice is cooked in a state where cooking water in which carbohydrates are dissolved in water is added to the raw material rice.

4. 3. The method for producing cooked rice according to claim 1 or 2, characterized in that the carbohydrate dissolved in the post-mixing liquid is any one of materials from a material group consisting of materials belonging to disaccharides, materials belonging to trisaccharides, materials belonging to tetrasaccharides, and materials belonging to sugar alcohols, or any combination of materials from the material group.

5. 3. The method for producing cooked rice according to claim 1 or 2, wherein the carbohydrate dissolved in the post-mixing liquid is any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof.

6. The method for producing cooked rice according to claim 3, characterized in that the carbohydrate dissolved in the cooking water is any one of materials from a group of materials consisting of materials belonging to disaccharides, materials belonging to trisaccharides, materials belonging to tetrasaccharides, and materials belonging to sugar alcohols, or any combination of materials from the group of materials.

7. 4. The method for producing cooked rice according to claim 3, wherein the carbohydrate dissolved in the rice cooking water is any one of trehalose, maltose, isomaltose, maltotriose, isomaltotriose, raffinose, panose, glucosylsucrose, stachyose, maltosyltrehalose, reduced starch syrup, and starch syrup, or any combination thereof.

Images