Modifier for cooked rice

Abstract

The present invention provides a cooked rice food modifier which offers improvement so that overheating-induced surface drying of cooked rice caused when cooked rice that has been distributed or stored under chilled conditions is heated with a microwave oven before eating is suppressed, and so that moderate hardness, stickiness and graininess of cooked rice are maintained. More specifically, provided is a cooked rice food modifier containing, as an active ingredient, α-amylase having the following characteristic properties (1) to (3): (1) the activity optimum temperature is 60°C to 80° C; (2) 50% or more of the activity is preserved after heating at 70°C for 60 minutes; and (3) the activity is lost by heating at 80°C for 60 minutes.

Description

Cooked rice improver

[0001] The present invention relates to a cooked rice food modifier containing a specific α-amylase enzyme, a method for producing a cooked rice food containing the modifier, and a method for modifying a cooked rice food.

[0002] It is known that cooked rice loses texture (elasticity, stickiness, etc.) over time, becoming hard and crumbly. This phenomenon, in which water separates and gelatinized starch hardens after being left standing, is generally called retrogradation. This retrogradation phenomenon is particularly pronounced when stored at low temperatures, making it problematic for long-term storage and long-distance distribution. Therefore, there is a demand for cooked rice that does not harden even when stored and distributed refrigerated.

[0003] In order to obtain such cooked rice, it has been reported that various enzymes such as α-amylase (Patent Documents 1 to 5) are added to cooked rice and then cooked.

[0004] On the other hand, cooked rice stored in refrigerated lunch boxes and other foods is often heated in a microwave oven or other device before eating. After heating, the water in the cooked rice evaporates, leaving it with a dry texture. Therefore, there is a demand for cooked rice with a good texture that prevents the surface from drying out.

[0005] Patent No. 3372652 Patent No. 5921515 International Publication No. 2022 / 131207 Special Publication No. 2015-525564 Special Publication No. 2004-290075

[0006] The present invention aims to provide a cooked rice food modifier that inhibits aging of cooked rice distributed or stored under chilled conditions, inhibits surface drying due to overheating that occurs when cooked rice is heated in a microwave oven before eating, and improves the cooked rice so that appropriate hardness, stickiness, and graininess are maintained.

[0007] As a result of extensive research to achieve the above object, the present inventors have found that cooked rice foods produced by adding an enzyme preparation containing an α-amylase with specific properties can be stored at low temperatures and heated in a microwave oven before eating, and the surface drying is suppressed, resulting in cooked rice that is excellent in hardness and stickiness as well as graininess and formability. They also found that the effect of improving cooked rice is further enhanced when hemicellulase and transglutaminase are used in combination, which led to the completion of the present invention.

[0008] That is, the present invention is as follows. [1] A cooked rice food modifier containing, as an active ingredient, (A) α-amylase having the following properties: (1) an optimal activity temperature between 60°C and 80°C; (2) at least 50% of the activity remains after heating at 70°C for 60 minutes; and (3) the activity is lost after heating at 80°C for 60 minutes. [2] The modifier according to [1], further containing at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase. [3] The modifier according to [1] or [2], wherein the cooked rice food is chilled cooked rice. [4] The modifier according to any of [1] to [3], wherein the cooked rice food modification is suppression of surface drying of the cooked rice food. [5] A method for producing a cooked rice food product, comprising a step of contacting raw rice with (A) α-amylase having the following characteristics: (1) an optimal activity temperature between 60°C and 80°C; (2) at least 50% of the activity remains after heating at 70°C for 60 minutes; or (3) the activity is lost after heating at 80°C for 60 minutes. [6] The method according to [5], further comprising a step of contacting the raw rice with at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase. [7] The method according to [5] or [6], in which 0.0001 to 1000 U of α-amylase is contacted per 1 g of raw rice. [8] The method according to [6] or [7], in which 0.0001 to 1000 U of hemicellulase is contacted per 1 g of raw rice. [9] The method according to any one of [6] to [8], in which 0.00001 to 100 U of transglutaminase is contacted per 1 g of raw rice.

[10] A method for improving the quality of cooked rice foods, comprising the step of contacting raw rice with (A) α-amylase having the following characteristics: (1) an optimal activity temperature between 60°C and 80°C; (2) at least 50% of the activity remains after heating at 70°C for 60 minutes; or (3) the activity is lost after heating at 80°C for 60 minutes.

[11] The method according to

[10] , further comprising the step of contacting the raw rice with at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase.

[12] The method according to

[10] or

[11] , in which 0.0001 to 1000 U of α-amylase is contacted per 1 g of raw rice.

[13] The method according to

[11] or

[12] , in which 0.0001 to 1000 U of hemicellulase is contacted per 1 g of raw rice.

[14] The method according to any one of

[11] to

[13] , wherein 0.00001 to 100 U of transglutaminase is contacted per 1 g of raw rice.

[0009] According to the present invention, cooked rice can be provided in which the surface drying of the cooked rice is suppressed and the cooked rice does not become dry even when the cooked rice is overheated in a microwave oven or the like before eating. According to the present invention, the cooked rice food can be stored at low temperatures for a long period of time while maintaining its texture. According to the present invention, cooked rice can be provided which is easy to loosen when mixed and therefore has excellent moldability.

[0010] Figure 1 shows the hardness of the grains of cooked rice samples after they have been microwaved. The vertical axis shows the maximum compressive load (g). Figure 2 shows the stickiness of the grains of cooked rice samples after they have been microwaved. The vertical axis shows the tensile area (g-seconds). Figure 3 shows the results of the disaggregation test of cooked rice samples after they have been microwaved. The vertical axis shows the maximum compressive load (g). Figure 4 shows the results of the disaggregation test of cooked rice samples after they have been microwaved. The vertical axis shows the maximum compressive load (g).

[0011] The present invention relates to a cooked rice food modifier (hereinafter sometimes abbreviated as the modifier of the present invention) containing α-amylase as an active ingredient, which has all of the following characteristics: (1) The optimum activity temperature is between 60°C and 80°C; (2) At least 50% of the activity remains after heating at 70°C for 60 minutes; and (3) The activity is lost after heating at 80°C for 60 minutes.

[0012] (A) α-Amylase The α-amylase used in the present invention is characterized by having the above-mentioned properties (hereinafter sometimes abbreviated as (A)). "The optimum temperature for activity is between 60°C and 80°C" means that the enzyme activity is, for example, 90% or more when the optimum temperature, which is the temperature at which the enzyme exerts its action, is between 60°C and 80°C. "At least 50% of the activity remains after heating at 70°C for 60 minutes" means that at least 50% of the enzyme activity is maintained even when the enzyme is heated at 70°C for 60 minutes. "The activity is lost after heating at 80°C for 60 minutes" means that the enzyme activity is lost, preferably completely, when the enzyme is heated at 80°C for 60 minutes.

[0013] The α-amylase used in the present invention may be commercially available or may be prepared from the culture medium of a microorganism that produces α-amylase. The preparation method may be any known protein separation and purification method (e.g., centrifugation, UF concentration, salting out, various types of chromatography using ion exchange resins, etc.). For example, an endo-type α-amylase may be used, which is obtained by culturing a strain selected from bacteria listed in the Official Compendium of Food Additives using a unique production method, and then purifying the resulting enzyme. A specific example is Cleustase SD8, available from Amano Enzyme Inc. Furthermore, (A) in the present invention is preferably an α-amylase derived from the genus Bacillus.

[0014] In the present invention, the activity unit of α-amylase is measured and defined as follows: α-amylase is allowed to act on blocked p-nitrophenyl maltoheptaoside as a substrate. The resulting p-nitrophenyl maltosaccharide is then decomposed with thermostable α-glucosidase, the reaction is stopped with trisodium phosphate, and the absorbance of the resulting p-nitrophenol at 400 nm is measured. The amount of enzyme that liberates 1 μmole of p-nitrophenol in 1 minute is defined as 1 U (unit).

[0015] The activity of (A) in the present invention contained per gram of the modifier of the present invention is usually 1 to 10,000 U, preferably 10 to 1,000 U, more preferably 50 to 500 U.

[0016] The modifying agent of the present invention may be added either before or during cooking of cooked rice. For example, the modifying agent of the present invention is typically added in an amount of 0.001 to 10% by weight, preferably 0.01 to 5% by weight, more preferably 0.02 to 1% by weight, and even more preferably 0.05 to 0.5% by weight, based on the total weight of raw rice. When the amount of enzyme required is extremely small, the modifying agent of the present invention may be prepared in a solution of a measurable concentration, and the solution may be diluted before addition.

[0017] In the present invention, the cooked rice food is not particularly limited as long as it contains rice, but examples include foods in which rice contributes to the texture and physical properties of the food. Specific examples include cooked rice (white rice, multigrain rice), vinegared rice (sushi rice), red rice, pilaf, fried rice, seasoned rice, sticky rice, rice porridge, risotto, rice balls, sushi, boxed lunches, rice noodles, rice bread, and chilled versions thereof, frozen foods, aseptically packaged foods, retort foods, dried foods, and canned foods. Among these, chilled and frozen cooked rice foods suitable for distribution and storage are preferred, with chilled cooked rice foods being more preferred. Note that "chilled" refers to "refrigerated," and "chilled foods" refers to foods stored at low temperatures of about 0°C to 10°C to maintain quality.

[0018] The cooked rice food modifier of the present invention improves the quality of cooked rice food, such as texture, or enhances its manufacturing suitability. Texture refers to the sensation of food when placed in the mouth, such as the chewiness and feel on the tongue. In the case of cooked rice, it refers to the elasticity (hardness), stickiness, and water retention (dryness) of the rice. Improving texture quality means suppressing the deterioration of texture that progresses over time or maintaining the texture at the level after production, but preferably means suppressing surface drying caused by heating when chilled cooked rice foods, such as chilled cooked rice foods, are heated in a microwave oven or the like, thereby achieving a texture and graininess similar to or better than that of cooked rice. Manufacturing suitability refers to whether the food is suitable for manufacturing with the desired quality, and refers to the ease of molding (loosening ability) when molding cooked rice. Improving manufacturing suitability means achieving a loosening ability similar to or better than that of cooked rice.

[0019] The modifying agent of the present invention may further contain hemicellulase and / or transglutaminase as an active ingredient.

[0020] (B) Hemicellulase "Hemicellulase" refers to a protein having the activity of catalyzing the reaction of hydrolyzing hemicellulose (sometimes abbreviated as (B)). Examples of hemicellulases include xylanases and mannanases. "Xylanase" is a protein having the activity of catalyzing the reaction of hydrolyzing xylan or complex polysaccharides containing xylan (such as arabinoxylan and glucuronoxylan). "Mannanase" is a protein having the activity of catalyzing the reaction of hydrolyzing mannan or complex polysaccharides containing xylan (such as glucomannan).

[0021] The origin of the hemicellulase is not particularly limited. Hemicellulase may be derived from any of microorganisms, animals, plants, etc., and may be a homologue of a known hemicellulase or an artificially modified version of such a homologue. Hemicellulase may be, for example, one obtained by heterologous expression (i.e., a recombinant enzyme). Hemicellulase may be, for example, a commercially available product or one obtained by appropriate production. Examples of commercially available hemicellulases include Hemicellulase "Amano" 90 (Amano Enzyme Co., Ltd.) and Sumiteam X (Shin-Nihon Chemical Industry Co., Ltd.).

[0022] Hemicellulase can be produced, for example, by culturing a microorganism that produces hemicellulase. The microorganism that produces hemicellulase may be one that inherently produces hemicellulase, or may be one that has been modified to produce hemicellulase. The microorganism that produces hemicellulase can be obtained, for example, by introducing a gene encoding hemicellulase into the microorganism so that it can be expressed. The culture conditions for the microorganism that produces hemicellulase are not particularly limited, as long as the microorganism can grow and hemicellulase is produced. The microorganism that produces hemicellulase can be cultured, for example, under normal conditions for culturing microorganisms such as bacteria and fungi.

[0023] As the hemicellulase, purified hemicellulase may be used, or a material containing hemicellulase may be used. Examples of materials containing hemicellulase include a culture of a microorganism that produces hemicellulase, a culture supernatant separated from the culture, bacterial cells separated from the culture, and a processed product of the bacterial cells. The hemicellulase may be purified to a desired degree. As the hemicellulase, one type of hemicellulase may be used, or two or more types of hemicellulases may be used in combination.

[0024] The activity of hemicellulase (e.g., xylanase) can be measured by the following procedure. Specifically, using a 10 mg / mL hemicellulose solution (e.g., a 10 mg / mL xylan solution) as a substrate, 1 mL of enzyme solution is added to 1 mL of substrate and 3 mL of 0.1 mol / L acetic acid / sodium acetate buffer (pH 4.5), and the mixture is allowed to react at 40°C for 30 minutes. 2 mL of Somogyi test solution is added, and the mixture is heated in a boiling water bath for 20 minutes, cooled, and 1 mL of Nelson's solution is added. The mixture is mixed until the cuprous oxide precipitate is completely dissolved, and water is added to make a 25 mL solution. After centrifugation, the change in absorbance at 500 nm is measured, and the amount of reducing sugar produced is calculated. In the case of hemicellulase (e.g., xylanase), the amount of enzyme that produces reducing sugar equivalent to 1 mg of xylose per minute in this reaction system is defined as 100 U (units).

[0025] (C) Transglutaminase Transglutaminase (protein-glutamine γ-glutamyltransferase) is a transferase (sometimes abbreviated as (C)) that catalyzes the reaction of condensing the amino group of a glutamine residue in a protein with a primary amine, transferring the substituent on the amine to the glutamine residue, and producing ammonia. Typically, the amino group of a lysine residue in a protein is used as the primary amine, and transglutaminase acts as a cross-linking enzyme.

[0026] As the transglutaminase, calcium-independent transglutaminase obtained from a microorganism is preferably used. Examples of calcium-independent transglutaminase derived from a microorganism include transglutaminase produced by actinomycetes belonging to the genus Streptomyces, which can be obtained according to the method described in Japanese Patent No. 2572716, but commercially available products such as "Activa TG-K" and "Activa TG-S" provided by Ajinomoto Co., Inc. and the like can also be used.

[0027] The enzymatic activity of transglutaminase can be measured and calculated, for example, by the hydroxamate method. That is, a reaction is carried out using benzyloxycarbonyl-L-glutaminylglycine and hydroxylamine as substrates, and an iron complex of the hydroxamic acid produced in the reaction is formed in the presence of trichloroacetic acid. The absorbance at 525 nm is then measured, and the amount of hydroxamic acid produced is determined from a calibration curve, thereby calculating the enzymatic activity. In this specification, 1 U is defined as the amount of enzyme that produces 1 μmol of hydroxamic acid per minute at 37°C and pH 6.0 (see JP-A-64-027471).

[0028] The modifier of the present invention may contain only (A), or may contain (A) and (B), (A and (C), or (A) to (C). The form of the modifier is not particularly limited as long as it contains the above components. For example, when the modifier of the present invention contains three components, (A) to (C) may be contained together, or may be in the form of a kit that is prepared separately and then combined before use.

[0029] When (A) and (B) are contained together, the activity of each enzyme contained per gram of the modifying agent of the present invention is as follows: (A): usually 1 to 10,000 U, preferably 10 to 1,000 U, more preferably 50 to 500 U, (B): usually 0.5 to 5,000 U, preferably 5 to 500 U, more preferably 10 to 200 U.

[0030] When (A) and (C) are contained together, the activity of each enzyme contained per gram of the modifying agent of the present invention is as follows: (A): usually 1 to 10,000 U, preferably 10 to 1,000 U, more preferably 50 to 500 U, (C): usually 0.1 to 2,000 U, preferably 1 to 200 U, more preferably 5 to 100 U.

[0031] When (A) to (C) are contained together, the activity of each enzyme contained per gram of the modifying agent of the present invention is as follows: (A): usually 1 to 10,000 U, preferably 10 to 1,000 U, more preferably 50 to 500 U, (B): usually 0.5 to 5,000 U, preferably 5 to 500 U, more preferably 10 to 200 U, (C): usually 0.1 to 2,000 U, preferably 1 to 200 U, more preferably 5 to 100 U.

[0032] In the case of a kit format in which the enzymes are prepared separately and then combined before use, the amount of enzyme contained in each preparation can be adjusted appropriately to achieve the above activity.

[0033] As mentioned above, the modifier of the present invention may be added either before or during cooking of cooked rice, but when two or more active ingredients are contained, the amounts to be added are as follows. When the modifier of the present invention contains (A) and (B) together, the modifier is used in an amount of 0.001 to 10 wt %, preferably 0.01 to 5 wt %, more preferably 0.02 to 1 wt %, and even more preferably 0.05 to 0.5 wt %, based on the total weight of raw rice. When the modifier of the present invention contains (A) and (C) together, the modifier is used in an amount of 0.001 to 10 wt %, preferably 0.01 to 5 wt %, more preferably 0.02 to 1 wt %, and even more preferably 0.05 to 0.5 wt %, based on the total weight of raw rice. When the modifying agent of the present invention contains (A) to (C) together, it is used in an amount of 0.001 to 10% by weight, preferably 0.01 to 5% by weight, more preferably 0.02 to 1% by weight, and even more preferably 0.05 to 0.5% by weight, based on the total weight of raw rice. When the amount of enzyme required is extremely small, the modifying agent of the present invention may be prepared into a solution of a measurable concentration, and the solution may be diluted before addition.

[0034] The ratio of each enzyme in the modifying agent of the present invention may be as follows: When (A) and (B) are contained together in the modifying agent of the present invention, the content of (B) is usually 0.0000001 to 10,000,000 U, preferably 0.00001 to 100,000 U, more preferably 0.001 to 1,000 U, and even more preferably 0.004 to 250 U per 1 U of (A). When (A) and (C) are contained together in the modifying agent of the present invention, the content of (C) is usually 0.00000001 to 1,000,000 U, preferably 0.000001 to 10,000 U, more preferably 0.0001 to 500 U, and even more preferably 0.001 to 50 U per 1 U of (A). When (A) to (C) are contained together in the modifier of the present invention, the contents of (B) and (C) per 1 U of (A) are usually 0.0000001 to 10,000,000 U of (B) and 0.00000001 to 1,000,000 U of (C), preferably 0.00001 to 100,000 U of (B) and 0.000001 to 10,000 U of (C), more preferably 0.001 to 1,000 U of (B) and 0.0001 to 500 U of (C), and even more preferably 0.004 to 250 U of (B) and 0.001 to 50 U of (C).

[0035] The modifier of the present invention may be added at any step in the production process of cooked rice foods, as described below. For example, after washing raw rice, 80 to 200 g of water (water content: 80 to 200 wt %) is usually added to 100 g of raw rice, and the modifier of the present invention is added in the above amount, followed by cooking.

[0036] In addition to the enzymes described above, the modifier of the present invention may further contain other food additives such as excipients such as dextrin, starch, modified starch, reduced maltose, seasonings such as meat extract, proteins such as vegetable protein, gluten, egg white, gelatin, casein, protein hydrolysates, partial protein hydrolysates, emulsifiers, chelating agents such as citrates and polymerized phosphates, reducing agents such as glutathione and cysteine, alginic acid, kansui (alkaline water), oils and fats, colorants, acidulants, flavorings, etc.

[0037] The modifier of the present invention may be in the form of a liquid, paste, granules, or powder, but from the viewpoint of maintaining functionality and storage stability, the modifier is preferably in the form of a powder.

[0038] The present invention also includes a method for producing a cooked rice food product, which comprises a step of contacting raw rice with (A) of the present invention (hereinafter sometimes abbreviated as "the production method of the present invention").

[0039] The production method of the present invention is characterized by including a step of contacting raw rice with (A), and may further include a step of contacting the raw rice with at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase.

[0040] Other steps that can be applied include, for example, the following conventional steps: (a) washing raw rice, (b) soaking raw rice in water, and (c) heating (cooking) raw rice together with an appropriate amount of water. In addition to the above, the process may include a cooling step, a step of adding other seasonings or additives, or a step of mixing with a seasoning, as appropriate.

[0041] In the production method of the present invention, the step of contacting (A) with raw rice is not particularly limited as long as it can bring raw rice into contact with (A). For example, (A) may be directly contacted with raw rice before or after the above steps (b) and (c), or an enzyme water prepared from (A) and water may be contacted with raw rice.

[0042] In the production method of the present invention, the step of contacting raw rice with (B) and / or (C) is not particularly limited as long as it is possible to contact raw rice with (B) and / or (C), as described above. For example, the enzyme may be directly contacted with raw rice before or after the above steps (b) and (c), or an enzyme water may be prepared from the enzyme and water and then contacted with the raw rice.

[0043] Furthermore, when (A) and (B) are contacted with raw rice, (A) and (B) may be contacted with the raw rice simultaneously or at different times. For example, (A) may be contacted with (A) in the above step (b) and (B) in the above step (c), or vice versa; (B) may be contacted with (A) in the above step (b) after the above step (c), or vice versa; (B) may be contacted with (A) in the above step (c) and after the above step (c), or vice versa. Contact of (A) and (C), and (A) to (C) can also be carried out in the same manner. It is particularly preferable to add (A) to (C) together to water in step (b) or (c).

[0044] In the production method of the present invention, the amount of (A) to be contacted (added) is usually an amount corresponding to an enzyme activity of 0.0001 to 1000 U per gram of raw rice, preferably 0.001 to 100 U, more preferably 0.01 to 10 U, and even more preferably 0.02 to 5 U. Within this range, aging of cooked rice foods is suppressed, and the surface of the cooked rice is prevented from drying out after cooking, thereby maintaining a good texture. When the amount of enzyme is extremely small, an enzyme solution of a measurable concentration may be prepared and then diluted before addition.

[0045] In the production method of the present invention, the amount of (B) to be contacted (added) is usually an amount corresponding to an enzyme activity of 0.0001 to 1000 U per gram of raw rice, preferably 0.001 to 100 U, more preferably 0.01 to 10 U, and even more preferably 0.02 to 5 U. Within this range, aging of cooked rice foods is suppressed, and the surface of the cooked rice is prevented from drying out after cooking, thereby maintaining a good texture. When the amount of enzyme is extremely small, the same procedure as above can be used.

[0046] In the production method of the present invention, the amount of (C) to be contacted (added) is usually an amount corresponding to an enzyme activity of 0.00001 to 100 U per gram of raw rice, preferably 0.0001 to 10 U, more preferably 0.001 to 5 U, and even more preferably 0.005 to 1 U. Within this range, aging of cooked rice foods is suppressed, and the surface of the cooked rice is prevented from drying out after cooking, thereby maintaining a good texture. When the amount of enzyme is extremely small, the same procedure as above can be used.

[0047] In the production method of the present invention, when (A) to (C) are used in combination, the contact (addition) amounts are typically 0.0001 to 1000 U for (A), 0.0001 to 1000 U for (B), and 0.00001 to 100 U for (C) per gram of raw rice, preferably 0.001 to 100 U for (A), 0.001 to 100 U for (B), and 0.0001 to 10 U for (C), more preferably 0.01 to 10 U for (A), 0.01 to 10 U for (B), and 0.001 to 5 U for (C), and even more preferably 0.02 to 5 U for (A), 0.02 to 5 U for (B), and 0.005 to 1 U for (C). This range inhibits aging of cooked rice foods, prevents surface drying of cooked rice after cooking, and maintains a good texture. Furthermore, when the amount of enzyme is extremely small, the same procedure as described above can be used.

[0048] In the production method of the present invention, when (A) and (B) are contacted, the amount of (B) to be contacted is usually 0.0000001 to 10,000,000 U, preferably 0.00001 to 100,000 U, more preferably 0.001 to 1,000 U, and even more preferably 0.004 to 250 U, relative to 1 U of (A). In the production method of the present invention, when (A) and (C) are contacted, the amount of (C) to be contacted is usually 0.00000001 to 1,000,000 U, preferably 0.000001 to 10,000 U, more preferably 0.0001 to 500 U, and even more preferably 0.001 to 50 U, relative to 1 U of (A). In the production method of the present invention, when (A) to (C) are contacted, the contact amounts of (B) and (C) are, relative to 1 U of (A), usually 0.0000001 to 10,000,000 U of (B) and 0.00000001 to 1,000,000 U of (C), preferably 0.00001 to 100,000 U of (B) and 0.000001 to 10,000 U of (C), more preferably 0.001 to 1,000 U of (B) and 0.0001 to 500 U of (C), and even more preferably 0.004 to 250 U of (B) and 0.001 to 50 U of (C).

[0049] The contact time (reaction time) of each enzyme is not particularly limited as long as it is a time that allows the enzyme to act on raw rice, but from the viewpoint of the cooking and manufacturing process of cooked rice foods, it can be 15 minutes to 3 hours, and 30 minutes to 90 minutes is preferred. The contact temperature (reaction temperature) is also not particularly limited as long as it is within a range in which the enzyme maintains its activity, but in view of characteristic (A), it is usually 5 to 100°C, preferably 40 to 80°C. The pH during contact with each enzyme is not particularly limited, but is usually 4 to 8. More specifically, it is preferably greater than 5.0 and equal to or less than 7.0, and more preferably equal to or greater than 5.5 and equal to or less than 6.0.

[0050] In the above (a) raw rice washing step, the raw rice is usually washed with water, and the washing time and washing temperature can be appropriately selected depending on the raw rice.

[0051] In the above step (b) of soaking raw rice in water, the soaking time varies depending on various conditions, but is usually 5 to 90 minutes at 5 to 50°C, preferably 15 to 60 minutes at 25 to 40°C.

[0052] In the above-mentioned step (c) of heating (cooking) raw rice together with an appropriate amount of water, the amount of water to be added is usually 80 to 200 g (water content: 80 to 200 wt %), preferably 100 to 170 g (water content: 100 to 170 wt %), more preferably 110 to 160 g (water content: 110 to 160 wt %), and even more preferably 120 to 150 g (water content: 120 to 150 wt %) per 100 g of raw rice, from the viewpoint of texture and physical properties after cooking.

[0053] The step of heating raw rice can be performed under normal pressure, but heating under pressure is also possible. Cooking can also be performed using a conventional rice cooker. The heating time is appropriately selected depending on the raw rice, and the heat level can be adjusted using conventional methods. The heating conditions are not particularly limited as long as the desired cooked rice food can be produced, and can be appropriately set depending on various conditions, such as the type of cooked rice food ingredient and the type of cooked rice food. The heating temperature can be, for example, the temperature at which the cooked rice food ingredient containing water boils, specifically, about 100°C. The heating time can be, for example, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, or 30 minutes or more, or 120 minutes or less, 90 minutes or less, 60 minutes or less, 40 minutes or less, or 30 minutes or less, or any combination thereof that is compatible. The heating time can be, for example, 10 to 120 minutes, 15 to 90 minutes, or 20 to 60 minutes.

[0054] In the production method of the present invention, when a step of cooling cooked cooked rice is included, the step is not particularly limited. For example, a cooling step in the process of producing chilled cooked rice or frozen cooked rice is exemplified. The chilled cooked rice food obtained in this manner is prevented from aging even when heated in a microwave oven, and a cooked rice food with a good texture in which the surface drying of the cooked rice is prevented is obtained.

[0055] The present invention also includes cooked rice foods obtained by the above-mentioned production method of the present invention using the modifier of the present invention. Examples of cooked rice foods include those exemplified above.

[0056] The present invention also includes a method for improving the quality of cooked rice foods, which comprises a step of contacting raw rice with (A) of the present invention (hereinafter sometimes abbreviated as "the method of the present invention").

[0057] The method of the present invention is characterized by including a step of contacting raw rice with (A), and may further include a step of contacting raw rice with at least one enzyme selected from the group consisting of (B) hemicellulase and (C) transglutaminase. The definitions of the modification and the preferred ranges of each enzyme are as described above.

[0058] The present invention will be further explained below with reference to examples, but the technical scope of the present invention is not limited by these examples. Furthermore, unless otherwise specified, the sensory evaluation in these examples was carried out using a well-trained expert panel with more than five years of experience in the food industry. In this specification, % represents % by weight unless otherwise specified.

[0059] [Test Example 1] Evaluation of the effect of active ingredients on improving cooked rice food (1) - Study of α-amylase - In this test, cooked rice was prepared by adding an active ingredient (α-amylase, hereinafter referred to as AA), and the effect of the active ingredient on improving cooked rice food was evaluated.

[0060] <Preparation of Cooked Rice> 400 g of raw rice was washed in water, and the water was replaced and washed again. The cooked rice food ingredients were then mixed with 540 g of water according to the formulations shown in Table 1, and the rice was cooked using a household rice cooker (Mitsubishi IH rice cooker NJ-LH064-R) to prepare cooked rice. AA represents the α-amylase of the present invention, and other types are shown in Table 2. The prepared cooked rice was packed into 200 g packs and stored at 5°C for 2 days, after which it was heated in a 500 W microwave for 2 minutes and 10 seconds (also known as microwave-warming) to prepare cooked rice samples.

[0061] The α-amylases (AA) used were as follows: Test Group 1A: Clistase SD8, an α-amylase derived from the genus Bacillus (Amano Enzyme Co., Ltd.). The properties of Clistase SD8 are as follows: (1) The optimum temperature for activity is between 60°C and 80°C. (2) At least 50% of the activity remains after 60 minutes of heating at 70°C. (3) The activity is lost after 60 minutes of heating at 80°C. The optimum pH for Clistase SD8 is 5.5 to 6.0. Test Group 2A: Biozyme A, an α-amylase derived from Aspergillus oryzae (Amano Enzyme Co., Ltd.). The properties of Biozyme A are as follows: (1) The optimum temperature for activity is 50°C. (2) The activity is completely lost after 60 minutes of heating at 70°C. (3) The activity is completely lost after 60 minutes of heating at 80°C. The optimum pH for Biozyme A is 5.0. Test group 3A: Kokugen SD-T, α-amylase derived from Bacillus licheniformis (Amano Enzyme Co., Ltd.). The properties of Kokugen SD-T are as follows: (1) The optimum temperature for activity is 90°C. (2) 100% activity remains after 60 minutes of heating at 70°C. (3) 100% activity remains after 60 minutes of heating at 80°C. The optimum pH for Kokugen SD-T is 6.0-7.0.

[0062]

[0063] <Sensory evaluation of cooked rice> The cooked rice was compared by sensory evaluation for drying inhibition, loosening, and grain texture. The sensory evaluation was performed by three trained panelists, and the average scores are shown in Table 2. The definitions and evaluation criteria for the evaluation were as follows.

[0064] <Definitions and evaluation criteria for evaluation> (1) Drying suppression: Degree of drying of the rice grain surface +3: Very dry suppressed +2: Dry suppressed +1: Slightly dry suppressed 0: Equivalent to the standard -1: Dry -2: Very dry

[0065] (2) Breaking: Breaking of the bolus when chewed +3: Too much breakage +2: Moderately well breakage +1: Breaking 0: Equivalent to the standard -1: Difficult to break down -2: Very difficult to break down

[0066] (3) Graininess: The degree to which the outline of each grain of rice can be felt +3: Very strong +2: Strong +1: Slightly strong 0: Equivalent to the standard -1: Slightly weak -2: Weak

[0067] (4) Overall rating: Preference for rice +3: Very favorable +2: Favorable +1: Somewhat favorable 0: Equivalent to the standard -1: Somewhat unfavorable -2: Unfavorable

[0068]

[0069] <Results> The results are shown in Table 2. In the control group, the rice became sticky lumps after reheating in the microwave, and it did not easily separate. Test group 1A showed clearer separation compared to the control group, and the rice was inhibited from drying and had a grainy texture. Test group 2A had almost the same properties as the control group, and although drying was inhibited, the rice did not separate or have a grainy texture. Test group 3A showed more significant separation compared to the control group, but the rice was too separate for cooked rice, and drying was not inhibited, making it undesirable. These results confirmed that claistase has a drying-inhibiting effect and is useful for imparting a grainy texture and moderate separation.

[0070] <Quantitative Evaluation of Cooked Rice> In this test, a compression test was carried out using a Texture Analyser for the cooked rice samples (control group, test groups 1A to 3A) prepared as described above.

[0071] (1) Hardness The grain hardness (the harder the grain, the drier it is) of the cooked rice sample after reheating in the microwave oven was evaluated by a compression test using a texture analyzer ("TA-XT plus" manufactured by Stable Micro Systems, hereafter abbreviated as TA). Specifically, a single grain of rice was placed in the center of the stage and compressed 90% at a speed of 1 mm / s using an acrylic plunger with a radius of 25 mm, measuring the maximum compression load. The results are shown in Figure 1. A larger compression load indicates a harder and drier grain, so a smaller value is preferable.

[0072] (2) Stickiness The stickiness of the grains, which indicates the degree of drying inhibition in cooked rice after microwave heating (the stickier the grain, the better the drying inhibition), was evaluated, for example, by a tensile test using TA. Specifically, after the compression test described above, the tensile area was measured, calculated from the gravitational force and time when pulled at a tensile speed of 1 mm / s. The results are shown in Figure 2. A larger tensile area indicates stickier grains and more inhibition of drying, so a larger value is preferable.

[0073] (3) Loosening Property (Moldability) The loosening property of cooked rice after reheating from the microwave was evaluated by a loosening property test using TA. Specifically, sushi rice balls made from 30 to 40 g of cooked rice were placed one by one in the center of a stage and compressed 50% at a speed of 2 mm / s using a stainless steel plunger with a radius of 10 cm. The maximum compression load was measured when the balls were compressed. The results are shown in Figure 3. The larger the compression load, the more difficult the rice balls were to loosen, and the smaller the compression load, the more they loosened. It is preferable for cooked rice to have an appropriate loosening property.

[0074] <Results> Figures 1 and 2 show that the rice grains in Test Plot 1A were the softest and maintained the most stickiness after microwave heating compared to the control plot and Test Plots 2A and 3A, demonstrating that drying was suppressed. Furthermore, Figure 3 shows that Test Plot 2A was as difficult to disintegrate as the control plot, and Test Plot 3A was too disintegrated, while Test Plot 1A had just the right amount of disintegration, confirming the same tendency as the sensory evaluation.

[0075] Test Example 2: Evaluation of the effect of active ingredients on improving cooked rice food (2) - Study of combinations - Cooked rice was prepared by adding (A) α-amylase, (B) hemicellulase, and (C) transglutaminase of the present invention as active ingredients, and the effect of the active ingredients on improving cooked rice food was evaluated. The products used were as follows: (A): Claistase SD8 (Amano Enzyme Inc.) (B): Hemicellulase "Amano" 90 (Amano Enzyme Inc.) (C): Activa TG (1000 U / g) (Ajinomoto Co., Inc.)

[0076] <Preparation of cooked rice> After polishing rice in the same manner as in Test Example 1, cooked rice food ingredients were blended according to the composition shown in Table 3 and cooked using a household rice cooker (Mitsubishi IH rice cooker NJ-LH064-R) to prepare cooked rice. The prepared cooked rice was packed into 200g packets and stored at 5°C for 2 days, after which it was heated in a microwave oven at 500W for 2 minutes and 10 seconds (also known as microwave-warming) to prepare cooked rice samples.

[0077] <Sensory evaluation of cooked rice> The loosening and stickiness of cooked rice were compared by sensory evaluation. The sensory evaluation was performed by three trained panelists, and the average score was calculated. The definitions and evaluation criteria for the evaluation were the same as those in Test Example 1.

[0078]

[0079] <Results> The average scores for each item are shown in Table 4.

[0080]

[0081] In the control group, the rice became sticky lumps after heating in the microwave, and it was difficult to separate. Test group 1B showed clearer separation than the control group, and the rice had reduced drying and a grainy texture. Test group 2B had better grain structure than test group 1B, making it a more desirable cooked rice. Test group 3B had improved separation compared to test group 1B, making it a more desirable cooked rice. Test group 4B not only had improved grain structure and separation compared to test groups 2B and 3B, but also reduced drying compared to test groups 2B and 3B, making it a very desirable cooked rice. These results confirmed that the combined use of TG and hemicellulase in addition to claistase has a high effect of preventing drying and can impart a grainy texture and moderate separation.

[0082] Test Example 3 Evaluation of the Effects of Active Ingredients on the Improvement of Cooked Rice Food (3) Three enzymes, which are active ingredients, were added to prepare cooked rice, and the effects of the active ingredients on the improvement of cooked rice food were evaluated.

[0083] <Preparation of cooked rice> After polishing rice in the same manner as in Test Example 1, cooked rice food ingredients were blended according to the composition shown in Table 5 and cooked in a household rice cooker (Mitsubishi IH rice cooker NJ-LH064-R) to prepare cooked rice. The prepared cooked rice was packed into 200g packs and stored at 5°C for 2 days, after which it was heated in a microwave oven at 500W for 2 minutes and 10 seconds (also known as microwave-warming) to prepare cooked rice samples.

[0084] <Sensory evaluation of cooked rice> The cooked rice was compared by sensory evaluation for drying inhibition, loosening, and grain texture. The sensory evaluation was performed by three trained panelists, and the average score was calculated. The definitions and evaluation criteria for the evaluation were the same as those in Test Example 1.

[0085]

[0086] <Results> The average scores for each item are shown in Table 6.

[0087]

[0088] In the control group, the rice became sticky lumps upon reheating in the microwave, and the rice did not easily separate. Test group 1C was preferable to the control group, and the effect of adding the enzymes was clearly evident. Test group 2C was preferable, with a clearer effect than test group 1C. Test group 3C was more preferable, with a more pronounced effect than test group 2C. Test group 4C was the most preferable rice in this test, with a good balance of graininess and separation, and a drying inhibition effect. Test group 5C was preferable, with similar drying inhibition and graininess to test group 4C, but was easier to separate. Test group 6C was less grainy than test group 4C, but the effect of adding the enzymes was clear. From these results, it was confirmed that the effect of adding the enzymes was observed in the range of 1 / 10 to 10 times the amount of each enzyme, and that a particularly preferable addition amount was 1 / 2 to 2 times the amount.

[0089] <Quantitative Evaluation of Cooked Rice> As in Test Example 1, the loosening properties of the cooked rice samples (control, test plots 1C to 6C) prepared above were evaluated by a loosening property test using TA after reheating in the microwave.

[0090] <Results> The results are shown in Figure 4. As can be seen from Figure 4, the loosening properties (moldability) were improved in all test plots compared to the control plot.

[0091] According to the present invention, it is possible to provide a cooked rice food and a chilled cooked rice food that have an excellent texture even when heated in a microwave oven. According to the present invention, the quality of the cooked rice food can be maintained even when stored at low temperatures for a long period of time, which can extend the expiration date and contribute to reducing food waste.

[0092] This application is based on patent application No. 2023-201125 filed in Japan, the contents of which are incorporated in their entirety herein.

Claims

1. A cooked rice food improver containing, as an active ingredient, (A) α-amylase having the following characteristics: (1) The optimum activity temperature is between 60°C and 80°C. (2) More than 50% of the activity remains when heated at 70°C for 60 minutes. (3) The activity is lost when heated at 80°C for 60 minutes.

2. The modifying agent according to claim 1, further comprising at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase.

3. The modifier according to claim 1 or 2, wherein the cooked rice food is chilled cooked rice.

4. The modifier according to claim 1 or 2, wherein the modification of cooked rice food is to inhibit the surface drying of cooked rice food.

5. A method for producing a cooked rice food product, comprising a step of contacting raw rice with α-amylase having the following characteristics: (A) The optimum activity temperature is between 60°C and 80°C; (2) At least 50% of the activity remains when heated to 70°C for 60 minutes; (3) The activity is lost when heated to 80°C for 60 minutes.

6. The method according to claim 5, further comprising the step of contacting with at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase.

7. The method according to claim 5 or 6, wherein 0.0001 to 1000 U of α-amylase is contacted per gram of raw rice.

8. The method according to claim 6, in which 0.0001 to 1000 U of hemicellulase is contacted per gram of raw rice.

9. The method according to claim 6, wherein 0.00001 to 100 U of transglutaminase is contacted per gram of raw rice.

10. A method for improving cooked rice foods, comprising a step of contacting raw rice with α-amylase (A) having the following characteristics: (1) The optimum activity temperature is between 60°C and 80°C; (2) At least 50% of the activity remains when heated at 70°C for 60 minutes; (3) The activity is lost when heated at 80°C for 60 minutes.

11. The method according to claim 10, further comprising the step of contacting with at least one selected from the group consisting of (B) hemicellulase and (C) transglutaminase.

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