Method for producing cooked rice, method for producing chilled cooked rice and method for producing frozen cooked rice, and cooked rice, chilled cooked rice and frozen cooked rice

Abstract

We provide cooked rice that maintains its quality as cooked rice even after being stored for a long time, allowing it to be enjoyed deliciously. [Solution] A konjac fluid material having gelling power is prepared by a process of swelling and dissolving konjac powder in water, alkaline treatment at pH 9 or higher, and then reducing the pH to less than 8, or freeze-dried powder of said konjac fluid material, or a konjac fluid material having gelling power and a konjac powder content of 3.5% by weight or more, a viscosity of 4 Pa·s or less at 20°C, or said konjac fluid material is used as a rice cooking additive, and when cooking rice by mixing this rice cooking additive with rice and water, the amount of water relative to the rice in the mixture is in the range of 1.55 to 2.00 by weight, and the amount of rice cooking additive in the mixture is set to an amount such that the amount of konjac powder relative to the rice is in the range of 0.01 to 0.09% by weight.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing cooked rice and the like using konjac flowing material. The present invention also relates to cooked rice, refrigerated cooked rice, and frozen cooked rice.

Background Art

[0002] Konjac has long been a widely loved food among general consumers. It has been eaten as a single item or cooked in combination with other ingredients. Also, due to the recent diet boom, konjac has come to be regarded as a low-calorie healthy food, and konjac-containing foods incorporating konjac into various foods have been developed.

[0003] For example, a pasty substance has been proposed in which konjac solidified by adding an alkali is finely cut to facilitate mixing with other food ingredients or beverages (Patent Document 1). As another method, it has also been proposed to mix purified water-soluble konjac mannan obtained by purifying the water-soluble konjac mannan contained in konjac powder with other food ingredients or beverages (Patent Document 2). Furthermore, as another method, it has been proposed to subject the konjac mannan contained in konjac powder to enzymatic treatment to obtain a liquid substance (Patent Document 3). Also, konjac jelly obtained by adding water and an alkali to konjac powder and swelling / reacting it (Patent Document 4), a konjac flowing material obtained by subjecting konjac jelly to enzymatic treatment after reducing its pH value (Patent Document 5), a konjac flowing material prepared by reducing the pH of an alkaline swelling solution containing a high concentration of konjac powder and vigorously stirring it (see Patent Documents 6 and 7) have been proposed to be added to foods, used as an active ingredient in pharmaceuticals, or added to cosmetics (see Patent Document 8). Furthermore, it has also been proposed to add a konjac flowing material to frozen confections such as ice cream (Patent Document 9).

[0004] Furthermore, Patent Document 10 describes the use of a konjac fluid material with gelling ability, prepared by treating a paste-like substance of konjac powder swollen and dissolved in water with alkali at a pH of 9 or higher, and then reducing the pH, as an additive for cooking rice and the like. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-207854 [Patent Document 2] Special Publication No. 54-20582 [Patent Document 3] Japanese Patent Application Publication No. 5-199856 [Patent Document 4] Japanese Patent Publication No. 2002-335880 [Patent Document 5] Japanese Patent Publication No. 2002-335899 [Patent Document 6] Japanese Patent Publication No. 2007-185113 [Patent Document 7] International Publication No. 2007 / 080894 [Patent Document 8] Japanese Patent Publication No. 2013-1641 [Patent Document 9] Japanese Patent Publication No. 2016-34244 [Patent Document 10] Japanese Patent Publication No. 2019-77977 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, convenience stores and supermarkets sell refrigerated foods containing cooked rice, such as rice balls and bento boxes. Because these refrigerated foods containing cooked rice have short expiration or best-before dates, frequent delivery and display of products is necessary to ensure that consumers receive products with sufficient shelf life. However, due to the recent shortage of drivers in the logistics industry, it is becoming increasingly difficult to meet this need year after year. In addition, food that has passed its best-before or expiration date is usually discarded and incinerated, and in the case of refrigerated foods with short shelf lives, the amount of waste is considerable. Therefore, the CO2 emissions from incineration and the environmental burden from landfilling of incinerated waste are considered to be significant. For these reasons, it is necessary to take some measures to allow foods containing cooked rice to be preserved deliciously for a longer period than conventional products. Artificial preservatives have traditionally been used to prevent food spoilage. However, some artificial preservatives are suspected of being carcinogenic, raising concerns about their adverse health effects. Therefore, using naturally derived substances as food preservatives is being considered, but in reality, effective conditions for producing cooked rice with high shelf life using naturally derived substances have not yet been established.

[0007] Taking these current challenges into consideration, the inventors have diligently conducted research with the aim of providing cooked rice that maintains its quality as cooked rice even after being stored for a long period of time and can be enjoyed deliciously. [Means for solving the problem]

[0008] After extensive research, the inventors discovered that by using a konjac fluid material that meets specific conditions as a cooking additive, and by cooking the rice with this cooking additive mixed with rice and water, and by keeping the ratio of water to the cooking additive within a predetermined range, it is possible to obtain cooked rice that has excellent preservation properties and can be enjoyed with good texture and taste even after being stored for a long time. Based on this finding, the inventors have completed the present invention described below.

[0009] [1] A method for producing cooked rice, comprising cooking a mixture containing rice, water, and a cooking additive, wherein the cooking additive contains a gelling konjac fluid material or freeze-dried powder of the konjac fluid material, which is prepared by a process of swelling and dissolving konjac powder in water, alkali treatment at pH 9 or higher, and then reducing the pH to less than 8, or a konjac fluid material or freeze-dried powder of the konjac fluid material having a konjac powder content of 3.5% by weight or more, a viscosity of 4 Pa·s or less at 20°C, and having gelling power, the amount of water in the mixture relative to the rice is in the range of 1.55 to 2.00 times by weight, and the amount of the cooking additive in the mixture is in the range of 0.01 to 0.09% by weight relative to the rice. [2] The manufacturing method according to [1], wherein the amount of water in the mixture relative to the rice is 1.60 times by weight or more. [3] A method for producing refrigerated cooked rice, comprising cooling cooked rice produced by the manufacturing method described in [1] or [2] to 15°C or below. [4] The manufacturing method described in [3], wherein the weight of cooked rice when refrigerated is 2.4 times or more the weight of rice before cooking. [5] A method for producing frozen cooked rice, comprising freezing cooked rice produced by the manufacturing method described in [1] or [2]. [6] The manufacturing method described in [5], wherein the weight of cooked rice when frozen is 2.4 times or more the weight of rice before cooking. [7] Cooked rice produced by the manufacturing method described in [1] or [2]. Refrigerated cooked rice produced by the manufacturing method described in [8] [3] or [4]. Frozen cooked rice produced by the manufacturing method described in [9] [5] or [6]. [Effects of the Invention]

[0010] The present invention provides a method for producing cooked rice and refrigerated cooked rice that maintains its quality as cooked rice even after long-term storage, and allows consumers to enjoy a good texture and taste. Furthermore, the present invention provides a method for producing frozen cooked rice that maintains its quality even after long-term frozen storage and thawing, and allows consumers to enjoy a good texture and taste as cooked rice. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below. The following descriptions of constituent elements may be based on typical embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. Also, in this specification, "long-term storage" means storage for 24 hours or more.

[0012] <Method for producing cooked rice> The present invention relates to a method for producing cooked rice, which involves cooking a mixture containing rice, water, and a cooking additive. The cooking additive includes a konjac fluid material having gelling power, prepared by a process of swelling and dissolving konjac powder in water, alkali treatment at pH 9 or higher, and then reducing the pH to less than 8, or freeze-dried powder of the konjac fluid material; or a konjac fluid material having gelling power, with a konjac powder content of 3.5% by weight or more, a viscosity of 4 Pa·s or less at 20°C, or freeze-dried powder of the konjac fluid material. In the production method of the present invention, the amount of water relative to the rice in the mixture is within the range of 1.55 to 2.00 by weight, and the amount of the cooking additive in the mixture is set to an amount such that the amount of konjac powder relative to the rice is within the range of 0.01 to 0.09% by weight. By cooking a mixture prepared with these proportions using the production method of the present invention, cooked rice is obtained that maintains its quality as cooked rice even after being left for a long time after cooking, and that can be enjoyed with good texture and taste. First, we will describe the rice cooking additive used in the manufacturing method of the present invention.

[0013] [Additive for cooking rice] The additive for cooking rice used in the present invention contains a konjac fluid material. The konjac fluid material used in the present invention is a konjac fluid material having a gelling power prepared through a process of swelling and dissolving konjac powder in water, performing an alkali treatment at pH 9 or higher, and then reducing the pH to less than 8, or a konjac fluid material having a konjac powder content of 3.5% by weight or more, a viscosity at 20°C of 4 Pa·s or less, and having a gelling power.

[0014] The konjac fluid material used in the present invention can be prepared by performing a step of obtaining an alkali composition by swelling and dissolving konjac powder in water and performing an alkali treatment at pH 9 or higher (hereinafter referred to as "step A"), and then performing a step of reducing the pH of the alkali composition to less than 8 (hereinafter referred to as "step B"), and is a fluid material characterized by having a gelling power. Here, "having a gelling power" means exhibiting a function of gelling by heating under alkaline conditions. Ordinary plate konjac has already gelled and thus does not gel further even when heated under alkaline conditions. Also, a product obtained by swelling konjac powder in water and then decomposing it for a long time with an enzyme or the like to reduce its molecular weight does not gel even when heated under alkaline conditions, despite being a composition derived from konjac powder. The konjac fluid material used in the present invention is characterized in that it is manufactured by a specific manufacturing method and also has both fluidity and gelling power.

[0015] The step of swelling and dissolving konjac powder in water and performing an alkali treatment at pH 9 or higher (step A) is a step of obtaining an alkali composition by partially utilizing the gelling power of konjac powder. In the conventional method for producing konjac, the gelling power of konjac powder is almost completely utilized to obtain solid konjac, but in step A of the present invention, the utilization of the gelling power of konjac powder is suppressed. That is, gelling is stopped in a state where it becomes paste-like or pasty when water is added and stirred. By suppressing gelling in such a state, it becomes possible to give the finally obtained konjac fluid material gelling power, and after mixing with other components, the gelling power can be exhibited.

[0016] The origin and type of the konjac powder used in step A are not particularly limited. Konjac tubers powdered as they are may be used, or those经过 purification steps may be used. Also, the konjac powder does not necessarily need to have a uniform particle size.

[0017] The alkali added to the konjac powder in step A is appropriately selected from those that can be used in foods or pharmaceuticals. Konjac powder usually gels under an alkali with a pH of 9 or higher. Therefore, the amount of alkali added to the konjac powder in step A is appropriately adjusted so as to be within such a pH range. Preferred is a mode of adding a basic amino acid, a basic salt, or a mixture of both as the alkali. As the basic amino acid, usually, arginine, histidine, lysine, citrulline, ornithine, etc., alone or in combination, are used. Particularly preferred are arginine or lysine. The basic amino acid is preferably added at 1.25 to 20% by weight based on the konjac powder. The basic amino acid has a high pH buffering property. Therefore, when using a basic amino acid, there is also an advantage that a stable pH can be obtained and it is easy to provide a composition with stable quality.

[0018] As basic substances, typically, organic salts such as sodium citrate, sodium tartrate, sodium malate, sodium acetate, sodium lactate, and sodium succinate, as well as phosphates such as sodium polyphosphate, sodium pyrophosphate, sodium metaphosphate, disodium phosphate, trisodium phosphate, potassium polyphosphate, potassium pyrophosphate, potassium metaphosphate, dipotassium phosphate, and tripotassium phosphate, as well as carbonates such as sodium carbonate, sodium bicarbonate, potassium carbonate, calcium carbonate, and magnesium carbonate, and sulfates such as potassium sulfate, sodium sulfate, calcium sulfate, and magnesium sulfate, and sodium hydroxide and potassium hydroxide, either alone or in combination, can be used. In this way, any basic salt that can be used in cosmetics can be used as a basic salt in the present invention.

[0019] Furthermore, to provide a buffering effect, it is possible to combine the various acids or acidic salts in a way that ultimately results in an alkaline pH. In this case, suitable acids and basic salts include citric acid, tartaric acid, malic acid, acetic acid, lactic acid, phosphoric acid, monosodium phosphate, monopotassium malate, etc. The amount used is preferably 0.01 to 20% by weight relative to the konjac powder.

[0020] Combining basic amino acids and basic salts can sometimes simplify manufacturing by effectively balancing their functions. Basic amino acids have high pH buffering capacity, resulting in a stable pH, but they also have the drawback of making it difficult to set the pH value arbitrarily. On the other hand, basic salts have low pH buffering capacity, but they have the advantage of allowing for arbitrary pH adjustment through the selection of substances. Therefore, by skillfully combining the two, it becomes possible to easily set the pH, suppress pH fluctuations due to raw materials and water used, and produce a uniform alkaline composition.

[0021] The pH should be adjusted to 9 or higher, preferably between 9.0 and 10.5, and more preferably between 9.3 and 10.2. A pH of 9.0 or higher facilitates efficient gelation. Conversely, a pH of 10.5 or lower tends to prevent problems such as syneresis and alkaline odor caused by excessive gelation.

[0022] There are no particular restrictions on the order in which water and alkali are added to konjac powder. For example, water may be added to the konjac powder to cause swelling and dissolution, and then alkali may be added and mixed to allow the reaction to proceed. Alternatively, water with alkali added may be added to the konjac powder to allow swelling and reaction to occur simultaneously. Or, alkali may be mixed with the konjac powder before adding water to cause swelling and dissolution. These methods may be combined as appropriate. In addition, water containing basic amino acids may be added to the konjac powder first, and then water containing basic salts may be added afterward. Any of these methods can be adopted as steps A, as long as swelling by water and reaction by alkali proceed.

[0023] As a preferred example, one can first add water to konjac powder to cause swelling and dissolution, then add basic amino acids, basic salts, or a mixture of both to the resulting konjac paste and mix well. Another preferred example is to pre-mix and dissolve basic amino acids, basic salts, or a mixture of both in water, and then use this solution to cause swelling and dissolution of the konjac powder. Yet another preferred example is to pre-mix basic amino acids, basic salts, or a mixture of both with konjac powder, and then add water and mix to cause swelling and dissolution.

[0024] The amount of water added is preferably 10 to 150 parts by weight, and more preferably 12 to 100 parts by weight, per 1 part by weight of konjac powder.

[0025] After adding water or alkali to konjac powder, it is preferable to allow the mixture to react thoroughly at room temperature or under heating. For example, a sufficient reaction can be achieved by treating the mixture at room temperature for 2 to 4 hours or at 60°C for 15 minutes to 1 hour. The temperature, time, and other conditions can be appropriately determined depending on the ratio of konjac powder to alkali, the method of addition, pH, and the type of cosmetic product to be made. Generally, a shorter reaction time is preferable when the pH is high, and a longer reaction time is preferable when the pH is low.

[0026] In step A, ingredients other than those mentioned above may be added, as long as they do not excessively impair the effects of the present invention. For example, emulsifiers, starches, oils and fats, seasonings or fragrances may be added as appropriate. The type and amount of these ingredients can be determined according to the type of cosmetic product to be made, the manufacturing conditions, the storage environment, etc. Furthermore, the addition of such ingredients and additives may be carried out in later steps (for example, steps B, C and / or D).

[0027] Next, we will describe the process (step B) of reducing the pH of the alkaline composition to less than 8. Step B is a step to reduce the pH of the alkaline composition obtained in Step A to less than 8. pH reduction is usually performed by adding an acid. The type of acid added is not particularly limited as long as it does not excessively inhibit the effects of the present invention. Typically, an organic acid solution such as lactic acid, acetic acid, citric acid, succinic acid, malic acid, tartaric acid, or gluconic acid is added. The acid may be added all at once, or continuously or intermittently. The pH is preferably adjusted to 4.6 to 7.5, and more preferably to 5 to 7. In particular, it is more preferable to control the pH to the target pH without performing any treatment that further increases the pH after adjusting it to a pH of less than 4.6, especially less than 5.

[0028] The konjac fluid material of the present invention may also be obtained by performing an enzyme treatment step (step C) and a step of cutting the granules contained in the enzyme-treated composition (step D) in addition to steps A and B described above. The konjac fluid material used in the present invention may also be obtained by performing only step C in addition to steps A and B.

[0029] In step C, the enzyme used for enzymatic treatment is preferably one or more enzymes selected from cellulase, hemicellulase, pectinase, protease, and galactomannase. Commercially available enzymes can be used. For example, sucrase N manufactured by Sankyo Co., Ltd. can be preferably used.

[0030] Enzyme treatment should be carried out at a temperature at which the enzyme can function effectively. Typically, this is done under heating conditions, preferably at 40-75°C, and more preferably at 50-70°C. The treatment time varies depending on the type of enzyme and temperature, but is usually 10 minutes to 12 hours, preferably 20 minutes to 6 hours, and even more preferably 30 minutes to 3 hours. Stirring is also preferable during the enzyme treatment.

[0031] After enzyme treatment, it is preferable to inactivate the enzyme. The means of inactivating the enzyme are not particularly limited as long as they do not excessively adversely affect the effects of the present invention, but the objective can be achieved, for example, by raising the temperature to a temperature at which the enzyme is inactivated. In the case of the aforementioned sucrase N, the enzyme can be inactivated by raising the temperature to, for example, 90°C.

[0032] Next, we will explain process D. Step D is a step of cutting the granules contained in the enzyme-treated composition obtained in Step C. Step C makes it possible to obtain a konjac fluid material that satisfies the viscosity conditions of the present invention, but if it is desired to further lower the viscosity of the composition obtained in Step C or to further reduce the size of the granules contained in the composition obtained in Step C, it is preferable to perform Step D. The viscosity can be further reduced by about 0.2 to 1 Pa·s.

[0033] The cutting performed in step D is preferably carried out using a homogenizer or food cutter. The details of the structure of the food cutter or homogenizer are not particularly limited. If the enzyme-treated composition obtained in step C contains lumps, it is sufficient to mechanically cut the lumps, and it is preferable to use a high-speed rotary cutter or a high-speed homogenizer. Such mechanical cutting can be repeated multiple times. By performing such cutting, it is possible to obtain a konjac fluid material with even better dispersion properties that is easily mixed uniformly with other components.

[0034] In the present invention, a high-concentration konjac fluid material having a konjac powder content of 3.5% by weight or more, a viscosity of 4 Pa·s or less at 20°C, and gelling ability can be preferably used. Such a high-concentration konjac fluid material can be prepared by preparing a high-concentration alkaline composition in step A and performing forced stirring in step B. Specifically, in step A, the amount of water added per 1 part by weight of konjac powder is preferably 10 to 27 parts by weight, more preferably 11 to 23 parts by weight, even more preferably 12 to 20 parts by weight, and particularly preferably 13 to 18 parts by weight. The composition obtained in step A has high viscosity and cannot be sufficiently mixed with other components as is. Therefore, in step B, the pH of the alkaline composition is reduced to less than 8, and the temperature is raised while forcibly stirring to obtain a forcibly stirred composition. "Forcible stirring" here means rotating a stirring means introduced into the alkaline composition at 30 rpm or more, or performing equivalent stirring, against the viscosity of the alkaline composition. Examples of stirring means include a rotating shaft with 2 to 12 blades. The temperature is gradually increased while performing such forced stirring. The range of temperature increase is preferably 5 to 60°C, more preferably 10 to 55°C, and even more preferably 20 to 50°C. It is also preferable to start with a low rate of temperature increase and gradually increase it. The final temperature reached in step B is preferably 40 to 75°C, more preferably 50 to 70°C. In step B, it is preferable to increase the stirring speed as the temperature rises. It is preferable to increase the stirring speed to 1.5 times or more, more preferably 1.8 times or more, and particularly preferable to increase it to 2 times or more. Specifically, a preferred embodiment can be exemplified by increasing the rotation speed from 30 rpm to 60 rpm while raising the temperature from room temperature to 60°C. The stirring time is preferably 2 to 45 minutes, more preferably 3 to 30 minutes, and particularly preferably 5 to 20 minutes. After performing step B, it is preferable to perform step C, and even more preferable to perform up to step D.

[0035] The konjac powder content of the high-concentration konjac fluid material is more preferably 4% by weight or more, more preferably 4.5% by weight or more, even more preferably 5% by weight or more, and particularly preferably 5.5% by weight or more. There is no particular upper limit, but for example, a konjac fluid material with 8% by weight can be obtained. Furthermore, the viscosity of the high-concentration konjac fluid material at 20°C is more preferably 3.5 Pa·s or less, even more preferably 3 Pa·s or less, and particularly preferably 2.8 Pa·s or less. The lower limit is preferably 0.1 Pa·s or more, more preferably 0.2 Pa·s or more, even more preferably 0.3 Pa·s or more, and particularly preferably 0.4 Pa·s or more. When defined as a range, the viscosity of the high-concentration konjac fluid material at 20°C is preferably 0.1 to 4 Pa·s, more preferably 0.1 to 3.5 Pa·s, even more preferably 0.2 to 3.2 Pa·s, even more preferably 0.3 to 3 Pa·s, and particularly preferably 0.4 to 2.8 Pa·s.

[0036] High-concentration konjac fluid materials are characterized by their low viscosity despite containing a large amount of konjac powder, and their gelling ability. Konjac powder swells into a paste when exposed to water, but there is a limit to the amount of swelling that konjac powder inherently possesses. Therefore, it is not easy to manufacture fluid materials containing significantly more than 3% by weight of konjac powder. One possible method to obtain a fluid material containing a large amount of konjac powder is to decompose the konjac mannan (glucomannan) that makes up the konjac powder until its swelling ability is considerably reduced, and then dissolve or disperse it in water. However, adopting such a method is undesirable because it would prevent the gelling ability and bioactive properties of konjac mannan from being obtained. According to the above manufacturing method, it is possible to increase the concentration while maintaining the gelling ability and bioactive properties of konjac mannan, thus enabling the simple manufacture of konjac fluid materials that meet the above conditions.

[0037] In this invention, the konjac fluid material may be used as a rice cooking additive in its original form, or the freeze-dried powder of the konjac fluid material may be used as a rice cooking additive, or the konjac fluid material may be freeze-dried into a powder, and this freeze-dried powder may be returned to the konjac fluid material to be used as a rice cooking additive. Here, the freeze-drying of the konjac fluid material can be carried out according to the conventional freeze-drying method.

[0038] [Rice Cooking Process] In this invention, a mixture is prepared by mixing the above-mentioned rice cooking additive with rice and water, and cooked rice is obtained by cooking this mixture. In this invention, at the start of cooking, water is added to the mixture so that the amount of water relative to the rice is within the range of 1.55 to 2.00 times by weight. Here, "amount of water" refers to the amount of water used for mixing when the mixture is prepared by mixing the rice itself with water and cooking additives, and to the sum of the amount of water absorbed by the rice through soaking and the amount of water used for mixing when the mixture is prepared by mixing rice that has been soaked in water (hereinafter referred to as "water-soaked rice") with water and cooking additives. The amount of water absorbed by the rice through soaking can be determined by subtracting the weight of the rice before soaking from the weight of the water-soaked rice. In conventional rice cooking without the use of rice cooking additives, the amount of water relative to the rice at the start of cooking is usually 1.3 to 1.4 times the weight of the rice, and at most 1.5 times. This is because if the amount of water is greater than this range, the rice will turn into a porridge-like consistency. In contrast, in the present invention, by adding a rice cooking additive, even when cooking with 1.55 to 2.00 times the weight of the rice, the rice will not turn into a porridge-like consistency, and cooked rice with appropriate firmness and stickiness can be obtained. The amount of water relative to the rice in the mixture prepared in the present invention is 1.55 times the weight of the rice, preferably 1.60 times or more, for example 1.65 times or more, for example 1.72 times or more. Furthermore, the upper limit of the amount of water relative to the rice is 2.00 times the weight of the rice, preferably 1.9 times, for example 1.85 times.

[0039] Furthermore, in this invention, the rice cooking additive is blended so that, at the start of cooking, the amount of konjac powder relative to the rice in the mixture is within the range of 0.01 to 0.09% by weight. Here, "konjac powder" refers to the konjac powder used as a raw material for the rice cooking additive. For example, if 10g (containing 0.5g of konjac powder) from 500kg of konjac fluid material obtained using 25kg of konjac powder (raw material) is mixed with 1kg of rice and water to obtain a mixture, the amount of konjac powder relative to the rice is 0.05% by weight. Also, with this ratio, the amount of konjac powder relative to the rice can be brought within the range of 0.01 to 0.09% by weight by adding 2 to 18g of the rice cooking additive. Preferably, the amount of rice cooking additive in the mixture is such that the amount of konjac powder relative to the rice is 0.02 to 0.08% by weight, and more preferably 0.03 to 0.07% by weight. For example, you can choose from a range of 0.02 to 0.05 weight percent, or from a range greater than 0.05 weight percent and 0.08 weight percent or less. Thus, in this invention, the moisture content of the mixture used for cooking is relatively high, while the cooking additive is added in small amounts. As a result, cooked rice with excellent preservation properties is obtained, and the deliciousness is maintained even after long-term storage (see the examples below). Generally, it is expected that cooked rice deteriorates more easily as the moisture content increases, and that preservation properties worsen as the amount of cooking additive that imparts preservation decreases. However, contrary to this, the fact that cooked rice with excellent preservation properties was obtained with the blending ratio specified in this invention is an unexpectedly advantageous effect.

[0040] There are no particular restrictions on how the rice, water, and cooking additive are mixed, but examples include mixing rice sprayed with the cooking additive with water, mixing the cooking water and cooking additive beforehand and then mixing with the rice, mixing the rice and cooking additive first and then mixing with the cooking water, and mixing the cooking water, rice, and cooking additive simultaneously. The rice cooking additive used in this invention may be used after being mixed with other food additives. For example, it may be mixed with seasonings and water before being mixed with rice and water.

[0041] There are no particular restrictions on the method of cooking rice. Rice may be cooked automatically using a rice cooker, or manually using a pot. Furthermore, cooking methods may include using an electric heater, such as an electric rice cooker, using magnetic induction heating, such as an IH rice cooker, or using heat, such as cooking rice in an earthenware pot on a gas stove. When using a rice cooker, it may be a household rice cooker or industrial machinery such as factory equipment. Regardless of the cooking method used, using the rice cooking additive of the present invention will produce cooked rice with high moisture content, good texture, and good shelf life.

[0042] Cooked rice produced by the manufacturing method of the present invention may be consumed immediately or after storage. In this invention, "after storage" means after being left at room temperature (25°C) for 10 hours or more. If stored at a temperature other than room temperature, it means after the time has elapsed for the bacterial count to reach the same level as that of cooked rice left at room temperature for 10 hours. Normally, after 10 hours at room temperature, cooked rice loses moisture, becomes hard, its texture is significantly impaired, bacteria increase significantly, and it turns white with wax, making it unsuitable for consumption. Cooked rice produced by the manufacturing method of the present invention shows suppressed deterioration even after being left at room temperature for 24 hours, and can be enjoyed with good taste and texture (hardness, stickiness, etc.). Furthermore, leaving it at room temperature for 24 hours can improve stickiness, adhesion, and firmness. Therefore, even cooked rice that has been left for some time can be consumed in a tastier state than usual according to this invention. Rice cooked using the rice cooking additive of the present invention can preferably be consumed even after 24 hours or more have passed at room temperature. More preferably, it can be consumed even after 36 hours or more have passed at room temperature.

[0043] The cooked rice produced by the manufacturing method of the present invention can be mixed with vinegar to make sushi rice. By making sushi rice, it can be used as a cooked rice product for sushi. Sushi rice made from cooked rice produced by the manufacturing method of the present invention has good shelf life and high utility value. Furthermore, because the vinegar does not excessively penetrate from the surface to the interior of the cooked rice produced by the manufacturing method of the present invention, it has the advantage of maintaining its texture and taste even after storage, preserving the deliciousness and umami unique to cooked rice. For this reason, the present invention is extremely useful in industries such as sushi restaurants and sushi bento manufacturers.

[0044] Cooked rice produced by the manufacturing method of the present invention can be used for the same purposes as ordinary cooked rice. For example, it can be mixed with curry and served as curry rice. Cooked rice produced using the manufacturing method of the present invention has the characteristic of having fewer calories per unit weight compared to cooked rice of the same firmness produced without the use of cooking additives. For this reason, these products are useful as low-carbohydrate, low-calorie cooked rice. They are particularly useful when you want to avoid raising your blood sugar levels or when you are on a diet.

[0045] <Method for producing refrigerated cooked rice> Next, the method for producing refrigerated cooked rice according to the present invention will be described. The present invention relates to a method for producing refrigerated cooked rice, which involves cooling cooked rice produced by the "Method for Producing Cooked Rice" described above to 15°C or below. For a description of the "Method for Producing Cooked Rice," please refer to the description in the "Method for Producing Cooked Rice" section above. The cooked rice produced by the cooking method used in this invention retains its moisture content even after being stored at 15°C or below for a long period of time, and can be enjoyed with good texture and taste. Therefore, the refrigerated cooked rice produced by the manufacturing method of this invention can be stored at 15°C or below for a long period of time and can be suitably used as a product in convenience stores and other places that sell food products such as rice balls at 15°C or below. In this invention, it is preferable that the weight of cooked rice when refrigerated is 2.4 times or more the weight of rice before cooking. Here, the increase in the weight of rice when refrigerated relative to the weight of rice before cooking corresponds to the amount of water absorbed by the rice, and a weight ratio of 2.4 times or more between cooked rice when refrigerated and rice before cooking means that the cooked rice when refrigerated has absorbed sufficient water. The upper limit of the ratio between the weight of cooked rice when refrigerated and rice before cooking is, for example, 3 times, but it may also be set to 2.8 times.

[0046] <Method for manufacturing frozen cooked rice> The present invention relates to a method for producing frozen cooked rice, which involves freezing cooked rice produced by the "Method for Producing Cooked Rice" described above. For a description of the "Method for Producing Cooked Rice," please refer to the description in the "Method for Producing Cooked Rice" section above. The freezing of cooked rice according to the present invention preferably includes a step of rapidly freezing the cooked rice. Here, "rapid freezing" means that the core temperature of the food passes through the maximum ice crystal formation temperature range within 30 minutes and freezes. The "maximum ice crystal formation temperature range" is the temperature range in which ice crystals tend to grow larger during the freezing process of food, and usually refers to the temperature range of -1°C to -5°C in which food begins to freeze. Rapid freezing can be performed, for example, by blowing cold air of -30°C or lower onto the cooked rice. The storage temperature of the frozen cooked rice is, for example, -18°C or lower, preferably -20°C or lower, and more preferably -25°C or lower. Cooked rice produced using the method for producing cooked rice in this invention retains sufficient moisture content even after being frozen for a long period and then thawed, thus reproducing the texture and taste of cooked rice. Therefore, frozen cooked rice produced using the method for producing cooked rice in this invention can be sold as a frozen food to general consumers and food service businesses. Furthermore, those who purchase it can enjoy the texture and taste of cooked rice by thawing the frozen cooked rice as appropriate, or offer it to their customers. There are no particular restrictions on the thawing method. It may be thawed naturally by leaving it at room temperature, or it may be thawed by irradiating it with electromagnetic waves using a microwave oven or the like. Frozen cooked rice produced using the method for producing cooked rice in this invention also has high shelf life after thawing. In this invention, it is preferable that the weight of cooked rice when frozen is 2.4 times or more the weight of rice before cooking. Here, the increase in the weight of rice when frozen relative to the weight of rice before cooking corresponds to the amount of water absorbed by the rice, and a weight ratio of 2.4 times or more between cooked rice when frozen and rice before cooking means that the cooked rice has absorbed sufficient water when frozen. Such frozen cooked rice retains its texture and deliciousness even after being thawed after being frozen for a long period of time. The upper limit of the weight ratio between cooked rice when frozen and rice before cooking is, for example, 2.8 times. [Examples]

[0047] The present invention will be described in more detail below with reference to examples and test examples. The materials, reagents, proportions, procedures, etc., shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0048] [1] Manufacturing of rice cooking additives (Manufacturing Example 1) An alkaline composition with a pH of 12 was obtained by adding and mixing 20 kg of konjac flour and 1.8 kg of sodium phosphate to 1000 liters of water at 60°C and reacting for 30 minutes. 5 g of lactic acid (50% concentration) was mixed with 1 kg of the alkaline composition to adjust the pH to 3.7. Next, 0.05 parts by weight of an enzyme (enzyme name: Scrase N, main enzyme: pectinase, manufacturer: Sankyo Co., Ltd.) was added to 100 parts by weight of paste-like konjac at 60°C and reacting for 2 hours to produce a konjac fluid material, which was designated as rice cooking additive 1.

[0049] (Manufacturing example 2) An alkaline composition with a pH of 12 was obtained by adding and mixing 20 kg of konjac flour and 1.8 kg of sodium phosphate to 1000 liters of water at 25°C and reacting for 3 hours. Subsequently, rice cooking additive 2 was produced by carrying out the same process as in Production Example 1.

[0050] (Manufacturing Example 3) An alkaline composition with a pH of 9.3 was obtained by adding and mixing 60 kg of konjac flour and 2.15 kg of sodium carbonate to 1000 liters of water at 60°C and reacting for 30 minutes. An aqueous solution consisting of 1 kg of citric acid and 100 kg of water was added to the alkaline composition and forcibly stirred at room temperature. Forcible stirring was started by rotating a stirring device (rotating shaft with 10 blades) inserted into the batch containing each mixture at 30 rpm at room temperature, and the rotation speed was increased to 60 rpm as the temperature rose to 60°C. This resulted in a composition with a pH of 7.3. To 100 parts by weight of the obtained pH-adjusted composition, 0.05 parts by weight of enzyme (enzyme name: Scrase N, main enzyme: pectinase, manufacturer: Sankyo Co., Ltd.) was added and enzyme treatment was carried out at 60°C for 2 hours. After that, the temperature was raised to 90°C to inactivate the enzyme, and then the temperature was lowered to room temperature to obtain the enzyme-treated composition. Next, the granules contained in the resulting enzyme-treated composition were cut using a food cutter to produce rice cooking additive 3.

[0051] (Manufacturing examples 4-11) By varying the amount of citric acid used to 2 kg, 3 kg, 4 kg, 5 kg, 6 kg, 7 kg, 8 kg, and 9 kg, and performing the same process as in Production Example 3, alkaline compositions with pH 6.2, pH 5.6, pH 5.3, pH 5.0, pH 4.6, pH 4.4, pH 4.3, and pH 4.2 were obtained, and finally, rice cooking additives 4 to 11 were obtained.

[0052] (Manufacturing examples 12-20) Rice cooking additives 12-20 were produced by adding and mixing konjac flour and sodium carbonate in water at 25°C instead of 60°C, changing the reaction time to 3 hours, and carrying out the same process as in production examples 4-11.

[0053] (Manufacturing Example 21) Rice cooking additive 21 was manufactured by following the same process as in Manufacturing Example 1, except that no enzymatic treatment was performed.

[0054] Using the rice cooking additive 1 manufactured in Manufacturing Example 1, cooked rice was prepared and evaluated according to the following process. The amount of konjac powder contained in rice cooking additive 1 is 1.95% by weight.

[0055] [2] Production and evaluation of cooked rice (Example 1) 700g of polished rice (2023 harvest Koshihikari) was soaked in water for 60 minutes. After draining the water for 4 minutes, the weight was measured to be 910g. 20g of rice cooking additive and 927g of water were added to this 910g of soaked rice and mixed to form a mixture. This mixture was cooked in a round pot IH rice cooker for 36 minutes. After steaming for 30 minutes, it was loosened to obtain high-temperature cooked rice. It was then cooled to 25°C to obtain room-temperature cooked rice. The amount of water in the mixture immediately before cooking was 1.61 times the weight of the rice.

[0056] (Example 2) The amount of water in the mixture immediately before cooking was changed to 1.79 times the weight of the rice, and high-temperature cooked rice and room-temperature cooked rice were obtained using the same method as in Example 1.

[0057] (Example 3) The amount of water in the mixture immediately before cooking was changed to 1.70 times the weight of the rice, and the rice was cooked using a round-pot gas rice cooker. The other mixing ratios and procedures were the same as in Example 1 to obtain high-temperature cooked rice and room-temperature cooked rice.

[0058] (Example 4) The amount of water in the mixture immediately before cooking was changed to 1.77 times the weight of the rice, and high-temperature cooked rice and room-temperature cooked rice were obtained using the same method as in Example 3.

[0059] (Comparative Example 1) Without adding any cooking additives, the amount of water in the mixture immediately before cooking was changed to 1.40 times the weight of the rice, and high-temperature cooked rice and room-temperature cooked rice were obtained using the same method as in Example 1.

[0060] (Comparative Example 2) High-temperature cooked rice and room-temperature cooked rice were obtained by adding a rice cooking additive in an amount of konjac powder that was 0.1% by weight relative to the rice, and otherwise following the same method as in Example 1.

[0061] (evaluation) When the taste of room-temperature cooked rice was measured immediately after production using a taste meter manufactured by Satake Seisakusho, all samples showed high values ​​of 88% or higher, indicating good taste. Sensory evaluation of hardness and stickiness showed that the room-temperature cooked rice of Example 2 was superior to that of Example 1, and the room-temperature cooked rice of Example 4 was superior to that of Example 3. Furthermore, when the rice was cooked in an IH rice cooker with the same amount of water added as in Example 3, the room-temperature cooked rice of Example 3, which was cooked in a gas rice cooker, showed better sensory evaluation results than the room-temperature cooked rice cooked in an IH rice cooker. Furthermore, the weight of the room-temperature cooked rice in Examples 1-4, and the weight of the cooked rice after it had been cooled to 10°C, were all at least 2.4 times the weight of the rice before cooking. When the room-temperature cooked rice from each example and comparative example was left to stand at room temperature (25°C) for 24 hours, the room-temperature cooked rice from Comparative Example 1 showed deterioration and was confirmed to be unsuitable for consumption. On the other hand, the room-temperature cooked rice from Examples 1-4 and Comparative Example 2 were all suitable for consumption. However, while the room-temperature cooked rice from Examples 1-4 showed almost no change in taste, the room-temperature cooked rice from Comparative Example 2 showed a decrease of 2-3 points in taste value. Furthermore, the room-temperature cooked rice of Examples 1-4 showed improvement in stickiness and adhesiveness after being left to stand for 24 hours. Specifically, after 24 hours of standing, the room-temperature cooked rice of Example 3 showed improved stickiness, and the room-temperature cooked rice of Example 4 showed improved adhesiveness. The room-temperature cooked rice of Example 1 showed improved stickiness in addition to adhesiveness, and the room-temperature cooked rice of Example 2 showed improved firmness in addition to adhesiveness and stickiness. The room-temperature cooked rice of Comparative Example 1 deteriorated significantly in hardness and firmness after being left to stand for 24 hours, but no such significant deterioration was observed in the room-temperature cooked rice of Examples 1-4. These results indicate that the room-temperature cooked rice of Examples 1-4 has excellent storage properties. Furthermore, it can be reasonably inferred that if cooked rice is cooled to 15°C or below for storage testing, or if cooked rice is frozen for storage testing, the same trend as the evaluation results obtained for storage at room temperature described above will be obtained. [Industrial applicability]

[0062] Cooked rice and refrigerated cooked rice produced by the manufacturing method of the present invention maintain their quality even after long-term storage, and offer a good texture and taste. Furthermore, frozen cooked rice produced by the manufacturing method of the present invention maintains its quality as cooked rice even after long-term frozen storage and thawing, and can reproduce the texture and taste of cooked rice. Therefore, according to the present invention, it is possible to set longer shelf lives and expiration dates for cooked rice products, thereby reducing the frequency of product delivery and display, and reducing food waste. Thus, the present invention has high industrial applicability.

Claims

1. A method for producing cooked rice, comprising cooking a mixture containing rice, water, and a cooking additive, The aforementioned rice cooking additive contains a konjac fluid material having gelling power, prepared by a process of swelling and dissolving konjac powder in water, alkaline treatment at pH 9 or higher, and then reducing the pH to less than 8, or freeze-dried powder of said konjac fluid material, or a konjac fluid material having gelling power, with a konjac powder content of 3.5% by weight or more, a viscosity of 4 Pa·s or less at 20°C, or freeze-dried powder of said konjac fluid material. The amount of water relative to rice in the aforementioned mixture is within the range of 1.55 to 2.00 times by weight. A method for producing cooked rice, wherein the amount of the rice cooking additive in the mixture is such that the amount of konjac powder relative to the rice is within the range of 0.01 to 0.09% by weight.

2. The manufacturing method according to claim 1, wherein the amount of water in the mixture relative to the rice is 1.60 times by weight or more.

3. A method for producing refrigerated cooked rice, comprising cooling cooked rice produced by the manufacturing method described in claim 1 to 15°C or below.

4. The manufacturing method according to claim 3, wherein the weight of cooked rice when refrigerated is 2.4 times or more the weight of rice before cooking.

5. A method for producing frozen cooked rice, comprising freezing cooked rice produced by the manufacturing method described in claim 1.

6. The manufacturing method according to claim 5, wherein the weight of cooked rice when frozen is 2.4 times or more the weight of rice before cooking.

7. Cooked rice produced by the manufacturing method described in claim 1 or 2.

8. Refrigerated cooked rice produced by the manufacturing method described in claim 3 or 4.

9. Frozen cooked rice produced by the manufacturing method described in claim 5 or 6.