Frozen rice improver, frozen rice, rice that has been naturally thawed from frozen rice, and method for producing frozen rice.

Abstract

To provide frozen cooked rice from which cooked rice having excellent softness, stickiness, and granular feeling can be obtained even when naturally thawed after freezing, and to provide a frozen cooked rice improving agent used to realize such properties.SOLUTION: Provided is an improver for frozen cooked rice that is naturally thawed for consumption, wherein the raw material rice of the frozen cooked rice is rice satisfying specific conditions for amylose content [X] and moisture content [Y], the whole of the improver contains 0.003 to 0.1% by weight (solid content equivalent) of a specific extract derived from basidiomycetes, contains 5000 to 166500 units of α-glycosyltransferase and 150 to 5000 units of α-amylase with respect to 100 g of the improver, and the alpha-glycosyltransferase / said alpha-amylase (enzyme activity ratio ) is 0.5 to 500.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to frozen cooked rice that is suitable for consumption after natural thawing following freezing. [Background technology]

[0002] Frozen rice dishes are thawed and consumed by methods such as microwave heating, natural thawing, and, in the case of pre-cooked rice dishes like pilaf, direct heat thawing. For rice dishes that are preferred to be served warm, microwave heating or direct heat thawing is preferable. However, some rice dishes, such as sushi and onigiri, do not necessarily need to be eaten warm, or in fact, are better served cold. In recent years, there has been a growing demand for frozen rice dishes that can be easily and deliciously consumed simply by natural thawing without the need for any special equipment.

[0003] However, frozen cooked rice made using rice with a low moisture content or a relatively high amylose content will have a hard, non-sticky texture when thawed naturally. Therefore, when using such rice, the amount of water added is increased compared to normal cooking conditions. However, while increasing the amount of water makes the rice softer and stickier, it significantly reduces the texture of the individual grains.

[0004] Patent Document 1 discloses a quality improver for starch-containing frozen foods that contains trehalose and an ice crystallization inhibitor made of xylomannan derived from basidiomycetes, and can suppress both the retrogradation of starch during the freezing period and retrogradation after thawing. Example 1 describes cooked rice that was frozen and stored for one week using this quality improver, and then naturally thawed at room temperature. However, the naturally thawed cooked rice was hard and lacked stickiness, and was not satisfactory. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-050735 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide frozen cooked rice that retains its softness, stickiness, and grain texture even after natural thawing following freezing, and a frozen cooked rice improver used for this purpose. [Means for solving the problem]

[0007] The inventors of this invention conducted extensive research to solve the above problems and, as a result, discovered that rice cooked by adding a specific amount of a frozen rice improver containing a specific amount each of a basidiomycete-derived extract, α-glycosyltransferase, and α-amylase, along with a specific amount of water, retains good softness, stickiness, and grain texture even after natural thawing following freezing. This led to the completion of the present invention.

[0008] In other words, the first aspect of the present invention is a rice improver for frozen cooked rice, wherein the raw rice for the frozen cooked rice is rice that satisfies the following conditions (A) or (B) in terms of amylose content [X] (weight%) and moisture content [Y] (weight%), and the entire rice improver for frozen cooked rice contains 0.003 to 0.1% by weight (on a solid content basis) of an extract derived from basidiomycetes, and 5,000 to 166,500 units of α-glycosyltransferase and 150 units of α-amylase per 100g of the improver. This invention relates to a rice improver for frozen rice intended for consumption after natural thawing, comprising 5000 units, with an α-glycosyltransferase / α-amylase (enzyme activity ratio) of 0.5 to 500, and the extract being obtained by extracting a mixture of basidiomycete amount (wet weight) / total amount (weight ratio) of water, alkaline water, and ethanol at 40 to 160°C for 0.1 to 12 hours, after which the extract residue derived from basidiomycete has been removed. [Condition (A)] 11.5 ≤ X < 19 and 11 ≤ Y < 7.0 + 8.5 × {1 - [(X - 19.0) / 8.5] 2} 1 / 2 [Condition (B)] 19 ≤ X ≤ 25 and 11 ≤ Y ≤ 15.5

[0009] In the aforementioned frozen rice improver, it is preferable that the entire frozen rice improver contains 0.1 to 3.3% by weight of HM pectin.

[0010] The second aspect of the present invention relates to frozen cooked rice, which is prepared by cooking a rice cooking ingredient and then freezing it, wherein the rice cooking ingredient contains raw rice, solids contained in an extract derived from basidiomycetes, water, α-glycosyltransferase, and α-amylase, wherein per 100 parts by weight of the raw rice, the solids contained in the extract derived from basidiomycetes are 0.00003 to 0.003 parts by weight, water is 150 to 190 parts by weight, and per 100 g of the raw rice, α-glycosyltransferase is 50 to 5000 units and α-amylase is 1.5 to 150 units, the α-glycosyltransferase / α-amylase (enzyme activity ratio) is 0.5 to 500, and the raw rice is rice whose amylose content [X] (weight%) and moisture content [Y] (weight%) satisfy the above conditions (A) or (B), and is intended for consumption after natural thawing.

[0011] In the aforementioned frozen cooked rice, it is preferable that the cooking ingredients contain 0.001 to 0.1 parts by weight of HM pectin per 100 parts by weight of the raw rice.

[0012] In the aforementioned frozen cooked rice, it is preferable that the cooking ingredients contain 1 to 3 parts by weight of the frozen cooked rice improver per 100 parts by weight of the raw rice.

[0013] The third aspect of the present invention relates to rice that has been naturally thawed from frozen rice.

[0014] The fourth aspect of the present invention is a method for producing frozen cooked rice for consumption after natural thawing, comprising cooking a rice cooking ingredient and then freezing it, wherein the rice cooking ingredient comprises raw rice, solids contained in an extract derived from basidiomycetes, water, α-glycosyltransferase, and α-amylase, wherein per 100 parts by weight of the raw rice, the solids contained in the extract derived from basidiomycetes are 0.00003 to 0.003 parts by weight, the water is 150 to 190 parts by weight, and per 100g of the raw rice, the α-glycosyltransferase is 50 to 5000 units and the α-amylase is 1.5 to 150 units. The present invention relates to a method for producing frozen cooked rice for consumption after natural thawing, wherein sea urchin is mixed with the α-glycosyltransferase / α-amylase (enzyme activity ratio) to be 0.5 to 500, the raw rice is rice that satisfies the conditions (A) or (B) above in terms of amylose content [X] (weight%) and moisture content [Y] (weight%), and the extract is obtained by extracting a mixture in which the amount of basidiomycetes (wet weight) / total amount (weight ratio) of water, alkaline water and ethanol is 0.05 to 10 at 40 to 160°C for 0.1 to 12 hours, and then removing the extract residue derived from basidiomycetes. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide frozen cooked rice that retains its softness, stickiness, and grain texture even after natural thawing following freezing, as well as a frozen cooked rice improver used for this purpose. [Brief explanation of the drawing]

[0016] [Figure 1] This graph shows the conditions (A) or (B) regarding the amylose content [X] (weight%) and moisture content [Y] (weight%) in raw rice according to one embodiment of the present invention, as regions (A) or (B). Let (X,Y), and points A(11.5,11), B(19,11)[=point G], C(25,11), D(25,15.5), and E(19,15.5) are shown on the graph. Region (A) is the region enclosed by points A, B and E, and region (B) is the region enclosed by points B, C, D and E. [Figure 2]It is a graph showing the condition (C) or (D) based on amylose content [X] (% by weight) and moisture content [Y] (% by weight) in raw material rice according to one embodiment of the present invention as region (C) or region (D). Letting it be (X,Y), point F(13,11), point G(19,11)[=point B], point H(21,11), point I(21,15), and point J(19,15) are shown on the graph. Region (C) is the region surrounded by points F, G and J, and region (D) is the region surrounded by points G, H, I and J. Mode for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described in further detail. The improver for frozen cooked rice of the present invention is an improver used for frozen cooked rice made from specific rice as a raw material, and contains a specific amount of an extract derived from basidiomycetes extracted under specific conditions, and specific amounts of α-glycosyltransferase and α-amylase, respectively.

[0018] In the present invention, frozen cooked rice means cooked rice that is frozen after rice cooking raw materials containing a specific amount of specific raw material rice are cooked. When a specific amount of the improver for frozen cooked rice is added during rice cooking, the cooked rice has good softness, stickiness and grain texture even after natural thawing after freezing. In the present invention, natural thawing means thawing at 0 to 30°C, and includes refrigerated thawing performed in a refrigerator or the like and microwave thawing. Here, "softness" differs from sticky soft rice grains, and means a texture in which each rice grain has appropriate softness and elasticity, and appropriate brittleness. In addition, "stickiness" means an appropriate sticky texture without dryness or crumbliness of rice grains. "Grain texture" means a texture in which rice grains do not bind to each other, that is, do not form lumps, and each individual rice grain can be perceived when eaten.

[0019] The raw material rice satisfies condition (A): 11.5≦X<19, 11≦Y<7.0+8.5×{1-[(X-19.0) / 8.5 where amylose content [X] (% by weight) and moisture content [Y] (% by weight) 2} 1 / 2or condition (B): it is preferable to satisfy 19≦X≦25 and 11≦Y≦15.5 (see FIG. 1), and condition (C): 13≦X<19, 11≦Y<11.0+4×{1-[(X-19.0) / 6 2} 1 / 2 or condition (D): it is more preferable to satisfy 19≦X≦21 and 11≦Y≦15 (see FIG. 2). Here, X is the amylose content (% by weight) in the raw rice, and Y is the moisture content (% by weight) in the raw rice. By using raw rice falling within the range of said condition (A) or said condition (B), the effects of the present invention can be easily obtained.

[0020] Said basidiomycete-derived extract is an extract obtained by subjecting a mixture, in which the total amount of basidiomycete (wet weight) / water, alkaline water and ethanol has a specific weight ratio, to an extraction treatment at a specific temperature for a specific time, and then removing extraction residues.

[0021] Said basidiomycetes are not particularly limited, and examples include basidiomycetes belonging to the Physalacriaceae family, basidiomycetes belonging to the Lyophyllaceae family, basidiomycetes belonging to the Amanitaceae family, basidiomycetes belonging to the Agaricaceae family, basidiomycetes belonging to the Coprinaceae family, basidiomycetes belonging to the Strophariaceae family, basidiomycetes belonging to the Gomphidiaceae family, basidiomycetes belonging to the Boletaceae family, basidiomycetes belonging to the Russulaceae family, basidiomycetes belonging to the Polyporaceae family, and basidiomycetes belonging to the Pleurotaceae family; specific examples thereof are as follows.

[0022] Basidiomycetes belonging to the Hypogynaceae family: such as *Lyophyllum decastes*, *Lyophyllum erythrorhizon*, *Lyophyllum shiitake*, *Lyophyllum spp.*, *Lyophyllum shiitake*, *Lyophyllum spp.*, *Lyophyllum shiitake*, *Lyophyllum erythrorhizon*, *Lyophyllum bellii*, *Lyophyllum erythrorhizonostreatus*, *Lactarius deliciosus*, *Lactarius porrigens*, *Lactarius deliciosus*, *Lactarius luteus*, *Lactarius luteus*, *Lactarius deliciosus*, *Lactarius luteus*, *Lactarius deliciosus*, *Lactarius luteus*, *Lactarius deliciosus*, etc. Basidiomycetes belonging to the Amanitaceae family: *Amanita caesarea*, *Lactarius luteus* Examples include basidiomycetes belonging to the Agaricaceae family, such as Amanita virosa; basidiomycetes belonging to the Coprinusaceae family, such as Coprinus comatus; basidiomycetes belonging to the Strophariaceae family, such as Pholiota nameko; basidiomycetes belonging to the Cortinariaceae family, such as Boletaceae; basidiomycetes belonging to the Russulaceae family, such as Ipomoea purpurea; basidiomycetes belonging to the Polyporaceae family, such as Maitake; and basidiomycetes belonging to the Pleurotaceae family, such as King oyster mushroom.

[0023] Among the aforementioned basidiomycetes, from the viewpoint of ease of availability, enoki mushrooms (Flammulina velutipes), hatake-shimeji mushrooms (Lyophyllum decastes), eringi mushrooms (Pleurotus eryngii), hon-shimeji mushrooms (Lyophyllum shimeji), and nameko mushrooms (Pholiota nameko) are preferred, with enoki mushrooms being more preferred.

[0024] The solvent used for extraction from the basidiomycetes is preferably at least one selected from the group consisting of water, alkaline water, and ethanol. From the viewpoint of the flavor and texture of cooked rice after natural thawing, water or alkaline water alone is more preferable, and alkaline water alone is even more preferable.

[0025] Regardless of whether or not water, alkaline water, or ethanol is included as a solvent, the content of water, alkaline water, and ethanol is preferably such that the ratio of the basidiomycete (wet weight) to the total amount of water, alkaline water, and ethanol (weight ratio) is 0.05 to 10, more preferably 0.1 to 5, and even more preferably 0.2 to 1. If the weight ratio is less than 0.05, the stickiness and graininess of the cooked rice after natural thawing may be inferior. Also, if the weight ratio exceeds 10, the extraction efficiency may decrease, which may increase the manufacturing cost of the frozen cooked rice improver.

[0026] The extraction temperature is preferably 40 to 160°C, more preferably 60 to 140°C, and even more preferably 70 to 120°C. If the extraction temperature is lower than 40°C, the extraction efficiency may be poor, and the stickiness and grain texture of the cooked rice after natural thawing may be inferior. Furthermore, if the extraction temperature exceeds 160°C, special pressurized equipment may be required, which may complicate the extraction method.

[0027] The extraction processing time is preferably 0.1 to 12 hours, more preferably 0.5 to 6 hours, and even more preferably 1 to 3 hours. If the extraction processing time is shorter than 0.1 hours, the extraction efficiency may be poor, or the stickiness and grain texture of the cooked rice after natural thawing may be inferior. Also, if the extraction processing time exceeds 12 hours, despite the time required for extraction, the effect on the softness, stickiness, and grain texture of the cooked rice after natural thawing may plateau, resulting in poor extraction efficiency.

[0028] The content of the basidiomycete-derived extract in the aforementioned frozen rice improver is preferably 0.003 to 0.1% by weight, more preferably 0.0044 to 0.05% by weight, and even more preferably 0.008 to 0.03% by weight, based on solid content. If the content of the basidiomycete-derived extract is less than 0.003% by weight, the stickiness and grain texture of the rice after natural thawing may be inferior. If the content is more than 0.1% by weight, the rice after natural thawing may be too soft, or an off-flavor from the basidiomycete-derived extract may be imparted.

[0029] The α-glycosyltransferase is a transferase that cleaves a portion of 1,4-α-glucan and forms new α-1,6 bonds intramolecularly and / or intermolecularly. There are no particular restrictions on the α-glycosyltransferase used, as long as it is suitable for food applications (grade); it can be appropriately selected, and commercially available products can be used as appropriate. An example of a commercially available product is "Sensea foam" (manufactured by Novozymes Japan).

[0030] The α-glycosyltransferase content in the aforementioned frozen rice improver is preferably 5,000 to 166,500 units, more preferably 5,800 to 36,000 units, and even more preferably 6,630 to 19,680 units per 100g of the improver. If the content is less than 5,000 units or more than 166,500 units, the grain texture of the rice after natural thawing may decrease.

[0031] The activity of the α-glycosyltransferase is defined as the amount of enzyme (amount of α-glycosyltransferase) that reduces the absorbance of the iodine-amylose complex at 660 nm by 1% per minute under standard conditions (pH 7.2, 60°C), with one unit being the amount of enzyme that reduces this absorbance by 1% per minute. The activity of the α-glycosyltransferase is measured as follows.

[0032] First, 10 mg of amylose type III (Sigma) is added to 0.5 ml of 2 M NaOH, then 1 ml of pure water is added, followed by 0.5 ml of 2 M HCl and 7.8 ml of phosphate buffer (pH 7.2) to prepare the substrate solution. Additionally, 100 μl of iodine / iodide stock solution is prepared by dissolving 0.26 g of iodine and 2.6 g of potassium iodide in 10 ml of pure water. 50 μl of 2 M hydrochloric acid is added to this solution, followed by 26 ml of pure water to prepare the stop reagent.

[0033] Then, 50 μl of the enzyme solution (α-glycosyltransferase aqueous solution) diluted to an absorbance of 0.15 to 0.3 is mixed with 50 μl of the substrate solution, and the mixture is incubated at 60°C for 30 minutes. After that, 2 ml of the stop reagent is added and mixed well, and the absorbance (X1) at 660 nm is measured. Then, the absorbance (X0) at 660 nm is measured in the same manner, except that the substrate solution is changed to phosphate buffer (pH 7.2).

[0034] On the other hand, the absorbance (Y1) at 660 nm is measured in the same manner as in the measurement of absorbance (X1), except that the enzyme solution (α-glycosyltransferase aqueous solution) is changed to pure water. Then, the absorbance (Y0) at 660 nm is measured in the same manner as in the measurement of absorbance (Y1), except that the substrate solution is changed to phosphate buffer (pH 7.2). The activity (U / ml) of the α-glycosyltransferase is calculated using the measured values ​​and the following formula. α-glycosyltransferase activity (U / ml) = {(X0-X1) / (Y0-Y1)} × 100 × dilution ratio × (1 / 30) × (1 / 0.05)

[0035] The α-amylase mentioned above refers to an enzyme that has the activity to cleave the linear structure (amylose) and branched structure (amylopectin) of starch molecules and break them down into dextrin and maltose. The α-amylase may be a commercially available product, for example, "Biozyme A" (manufactured by Amano Enzyme Co., Ltd.), "Novamil 10000BG", "Novamil 3DBG" (all manufactured by Novozymes Japan Co., Ltd.), "Sumizyme L", and "Sumizyme AS" (all manufactured by Shin Nippon Chemical Industries, Ltd.).

[0036] The α-amylase content is preferably 150 to 5000 units, more preferably 430 to 3360 units, and even more preferably 750 to 1730 units per 100g of the improving agent. If the content is less than 150 units, the stickiness and graininess of the cooked rice after natural thawing may decrease. If the content is more than 5000 units, the softness of the cooked rice after natural thawing may decrease.

[0037] The activity of the α-amylase is defined as the amount (ml) of 1% soluble starch that is decomposed when soluble starch is reacted with the α-amylase as a substrate at pH 5.0 and 40°C for 30 minutes. One unit is defined as the amount of enzyme (α-amylase) that decomposes 1 ml of 1% soluble starch. The activity of the α-amylase is measured by the standard analytical method of the National Research Institute of Brewing. Specifically, it is as follows:

[0038] Mix 5.9 ml of Solution A (11.55 ml glacial acetic acid mixed with 1000 ml of pure water) with 14.1 ml of Solution B (27.21 g sodium acetate dissolved in pure water mixed with 1000 ml). If the pH is not exactly 5.0, adjust the pH to 5.0 using Solution A or Solution B to prepare a 0.2 mM acetate buffer solution. Add a small amount of hot water to 1 g of soluble starch, stir well, and boil for 1-2 minutes. Then add 20 ml of 0.01 M acetate buffer solution (pH 5.0) to adjust the pH to 5.0, and then add pure water to bring the volume to 100 ml to prepare a starch solution. Add 0.1 g of potassium iodide and 50 ml of 10% hydrochloric acid to 0.0317 g of iodine, and dissolve this in 1000 ml of pure water to prepare an iodine solution. Dissolve 0.176g of calcium acetate, 2.722g of sodium acetate, and 5.844g of sodium chloride in pure water to make 1000ml, and then add 10ml of 10% acetic acid to prepare a salt solution. Dilute the enzyme (α-amylase) as appropriate using this salt solution to prepare an enzyme solution (α-amylase solution).

[0039] Take 2 ml of the starch solution into a test tube and preheat at 40°C for 5 minutes. Add 0.1 ml of the enzyme solution (α-amylase solution) to start the reaction, and take 0.1 ml of the reaction solution at a time using a pipette. Transfer the reaction solution to a test tube containing 10 ml of the iodine solution, mix well, and while maintaining the temperature at 25°C, measure the transmittance (T%) by colorimetric measurement at 670 nm through an absorption cell with a path length of 10 mm. The transmittance (T%) is measured over time (every 0.5 or 1 minute).

[0040] For the colorimetric analysis, a control solution is prepared by mixing 2 ml of pure water with 0.1 ml of enzyme solution (α-amylase solution), taking 0.1 ml of this mixture, and adding 10 ml of the aforementioned iodine solution. From these series of T% values, the reaction time (t minutes) corresponding to 66% is determined.

[0041] The activity (U / ml) of the α-amylase is calculated using the reaction time and the following formula. α-amylase activity (U / ml) = 2 × (1 / 0.1) × (30 / t) × dilution ratio

[0042] In the additive for frozen cooked rice, the α-glycosyltransferase / α-amylase (enzyme activity ratio) is preferably 0.5 to 500, more preferably 1 to 100, and even more preferably 5 to 50. If the enzyme activity ratio is less than 0.5, the graininess of the cooked rice after natural thawing may decrease. If it is greater than 500, the stickiness of the cooked rice after natural thawing may decrease.

[0043] From the viewpoint of the softness and stickiness of the frozen rice after natural thawing, it is preferable to further add HM pectin to the frozen rice improver. The HM pectin content is preferably 0.1 to 3.3% by weight, more preferably 0.17 to 1.05% by weight, and even more preferably 0.23 to 0.56% by weight of the total amount of the frozen rice improver. If the HM pectin content falls outside the above range, the expected effect of improving the softness and stickiness of the rice after natural thawing may not be obtained.

[0044] Here, HM pectin refers to a polysaccharide mainly composed of methylated galacturonic acid and / or galacturonic acid, in which methylated galacturonic acid accounts for 50% by weight or more of the total galacturonic acid. The HM pectin may be a commercially available product, for example, product names "GENU YM115-LJ", "GENU JM-150-J" (both manufactured by CP Kelco), product names "SM-478", "SM-666" (both manufactured by San-Ei Gen F.F.I.), and product name "AYD5110SB" (manufactured by Unitech Foods).

[0045] The form of the frozen rice improver of the present invention is not particularly limited and can be liquid, paste, powder, or solid, but is preferably liquid. When formulating the frozen rice improver, excipients such as monosaccharides such as glucose and fructose; oligosaccharides such as sucrose, lactose, and maltose; starch hydrolysates such as dextrin and powdered starch syrup; maltooligosaccharides such as maltotriose, maltotetraose, maltopentaose, and maltohexaose; sugar alcohols such as sorbitol, mannitol, maltitol, and powdered reduced starch syrup; and whey protein can be used.

[0046] Furthermore, the frozen rice improver may contain optional components as long as it does not impair the objective of the present invention. Examples of such optional components include gelatin; polysaccharides such as xanthan gum and pullulan; food emulsifiers such as glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, and lecithin; starches made from grains such as wheat, corn, waxy corn, potatoes, waxy potatoes, tapioca, rice, and glutinous rice; modified starches such as hydroxypropyl starch and hydroxypropylated phosphate cross-linked starch, which are obtained by chemically treating these starches; organic acids such as acetic acid, lactic acid, and citric acid; grain vinegars made from grains such as rice, wheat, and corn; fruit vinegars made from fruit juices such as apples and grapes; synthetic vinegars made from alcohol and acetic acid; processed vinegars to which flavorings and other concomitant components have been added; plum vinegar produced as a by-product during the production of pickled plums; and plum vinegar that has been desalted or concentrated.

[0047] The frozen cooked rice of the present invention is prepared by cooking a rice cooking ingredient containing a specific amount of specific raw rice, and then freezing it. It contains a specific amount of raw rice that satisfies condition (A) or condition (B) in terms of amylose content [X] and moisture content [Y], a specific amount of solids contained in an extract derived from basidiomycetes, and specific amounts of α-glycosyltransferase and α-amylase, respectively.

[0048] Said rice cooking raw material preferably comprises raw rice having an amylose content [X] (% by weight) and a moisture content [Y] (% by weight) that satisfy condition (A): 11.5≦X<19, 11≦Y<7.0+8.5×{1-[(X-19.0) / 8.5 2} 1 / 2 or condition (B): 19≦X≦25, 11≦Y≦15.5, and more preferably comprises raw rice having an amylose content [X] (% by weight) and a moisture content [Y] (% by weight) that satisfy condition (C): 13≦X<19, 11≦Y<11.0+4×{1-[(X-19.0) / 6 2} 1 / 2 or condition (D): 19≦X≦21, 11≦Y≦15. Here, X is the amylose content (% by weight) in said raw rice, and Y is the moisture content (% by weight) in said raw rice. By satisfying the range of said condition (A) or said condition (B), the effect of the present invention can be easily obtained.

[0049] In said rice cooking raw material, the content of the raw rice that satisfies said condition (A) or condition (B) is preferably 70 to 100% by weight, more preferably 80 to 100% by weight, and still more preferably 90 to 100% by weight based on the total weight of the rice cooking raw material. If the content is less than 70% by weight, the effects of the present invention, i.e., good softness, stickiness and grain texture of cooked rice after natural thawing, may not be obtained in some cases.

[0050] In said rice cooking raw material, the water content is preferably 150 to 190 parts by weight, more preferably 160 to 185 parts by weight, and still more preferably 170 to 180 parts by weight relative to 100 parts by weight of the raw rice in said rice cooking raw material. If the water content is less than 150 parts by weight, the softness and stickiness of the cooked rice after natural thawing may be insufficient in some cases. If the water content is more than 190 parts by weight, the cooked rice after natural thawing may be excessively soft or have insufficient grain texture in some cases. Note that said water content includes the amount of water absorbed during washing of the raw rice.

[0051] The content of the basidiomycete-derived extract in the rice cooking ingredients is preferably 0.00003 to 0.003 parts by weight, more preferably 0.0001 to 0.0015 parts by weight, and even more preferably 0.0002 to 0.00075 parts by weight, based on solid content, per 100 parts by weight of raw rice. If the content is less than 0.00003 parts by weight, the stickiness and grain texture of the cooked rice after natural thawing may be inferior. If the content is more than 0.003 parts by weight, the cooked rice after natural thawing may be too soft, or an off-flavor from the basidiomycete-derived extract may be imparted. The basidiomycete-derived extract contained in the rice cooking ingredients is the same as the basidiomycete-derived extract contained in the frozen cooked rice improver.

[0052] The amount of α-glycosyltransferase in the rice cooking ingredients is preferably 50 to 5000 units, more preferably 75 to 1000 units, and even more preferably 100 to 500 units per 100g of raw rice. If the amount is less than 50 units or more than 5000 units, the texture of the cooked rice after natural thawing may decrease. The α-glycosyltransferase contained in the rice cooking ingredients is the same as the α-glycosyltransferase contained in the frozen cooked rice improver.

[0053] The α-amylase content in the rice cooking ingredients is preferably 1.5 to 150 units, more preferably 10 to 100 units, and even more preferably 20 to 50 units per 100g of raw rice. If the content is less than 1.5 units, the stickiness and graininess of the cooked rice after natural thawing may decrease. If the content is more than 150 units, the softness and graininess of the cooked rice after natural thawing may decrease. The α-amylase contained in the rice cooking ingredients is the same as the α-amylase contained in the frozen cooked rice improver.

[0054] In the raw materials for cooking rice, the α-glycosyltransferase / α-amylase (enzyme activity ratio) is preferably 0.5 to 500, more preferably 1 to 100, and even more preferably 5 to 50. If the enzyme activity ratio is less than 0.5, the texture of the cooked rice after natural thawing may decrease. If it is greater than 500, the stickiness of the cooked rice after natural thawing may decrease.

[0055] From the viewpoint of the softness and stickiness of cooked rice after natural thawing, it is preferable to further include HM pectin in the rice cooking ingredients. The amount of HM pectin in the rice cooking ingredients is preferably 0.001 to 0.1 parts by weight, more preferably 0.003 to 0.03 parts by weight, and even more preferably 0.005 to 0.015 parts by weight, per 100 parts by weight of raw rice. If the amount falls outside the above range, the expected effect of improving the softness and stickiness of cooked rice after natural thawing may not be obtained. Note that the HM pectin contained in the rice cooking ingredients is the same as the HM pectin contained in the frozen cooked rice improver.

[0056] The solids, water, α-glycosyltransferase, α-amylase, and HM pectin contained in the basidiomycete extract of the raw materials for cooking rice may be added separately or as a blend, and the required amount can be easily added by adding them as the frozen rice improver.

[0057] When preparing frozen cooked rice using the aforementioned frozen cooked rice improver, the cooking ingredients may contain the frozen cooked rice improver, preferably in an amount of 1 to 3 parts by weight, more preferably 2 to 2.9 parts by weight, and even more preferably 2.5 to 2.8 parts by weight, per 100 parts by weight of the raw rice in the cooking ingredients. If the amount is less than 1 part by weight or more than 3 parts by weight, the softness, stickiness, and grain texture of the cooked rice after natural thawing may decrease.

[0058] One embodiment of the method for producing frozen cooked rice according to the present invention is illustrated below. The rice cooking ingredients are prepared by mixing 100 parts by weight of raw rice with 0.00003 to 0.003 parts by weight of solids contained in the extract derived from the basidiomycete, 150 to 190 parts by weight of water including the amount of water absorbed during washing, and α-glycosyltransferase and α-amylase in a ratio of 50 to 5000 units and 1.5 to 150 units per 100g of raw rice, and the α-glycosyltransferase / α-amylase (enzyme activity ratio) being 0.5 to 500, and then cooking the resulting rice cooking ingredients.

[0059] There are no particular restrictions on the cooking method. Cooked rice can be frozen as is, or after being packaged in small containers such as trays, retort pouches, or other film packs, and then rapidly frozen using conventional methods. When used as sushi rice, sushi rice can be prepared by adding seasonings such as vinegar immediately after cooking using conventional methods, shaping it into the form of nigiri sushi rice, or rapidly frozen after being combined with sushi toppings.

[0060] The frozen rice improver and frozen rice of the present invention are suitable for rice dishes such as sushi rice and onigiri that are eaten as is after being naturally thawed after freezing. However, they can also be used for rice dishes such as pilaf, fried rice, dry curry, brown rice, white rice, red bean rice, sticky rice, and mixed rice dishes that are often heated in a microwave oven or over an open flame. [Examples]

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these examples. In the examples, "parts" and "%" are based on weight.

[0062] The raw materials used in the examples and comparative examples are as follows: 1) Akita Komachi (pre-washed rice, amylose content [X]: 16.4% by weight, moisture content [Y]: 12.0% by weight) 2) "Sensea foam" manufactured by Novozymes Japan Co., Ltd. (25,000 units (U)) 3) Sumizyme AS (1500 units (U)) manufactured by Shin Nippon Chemical Industries, Ltd. 4) Novamyl 10000BG manufactured by Novozymes Japan Co., Ltd. 5) "Treha" manufactured by Hayashibara Co., Ltd. 6) CP Kelco "GENU pectin type JM-150-J" 7) CP Kelco's "Echo Gel K-OB" 8) Emulgy MS manufactured by Riken Vitamin Co., Ltd. 9) "Poem K30" manufactured by Riken Vitamin Co., Ltd. 10) "Ryoto Sugar Ester S-1170" manufactured by Mitsubishi Chemical Foods Corporation 11) "Sorbitol Ueno" manufactured by Ueno Pharmaceutical Co., Ltd. 12) Koshihikari rice (pre-washed rice, amylose content [X]: 16.5% by weight, moisture content [Y]: 14.5% by weight) 13) Kiyonishiki (Amylose content [X]: 18.0% by weight, Moisture content [Y]: 12.5% ​​by weight) 14) Nipponbare (amylose content [X]: 21.5% by weight, water content [Y]: 15.0% by weight) 15) Hoshiyutaka (Amylose content [X]: 25.5% by weight, Moisture content [Y]: 13.6% by weight)

[0063] <Evaluation of frozen rice> Each frozen rice sample obtained in the examples and comparative examples was naturally thawed by storing it at 25°C for 4 hours. Ten experienced panelists then evaluated the rice samples, and the average of their scores was used as the sensory evaluation. The evaluation criteria were as follows:

[0064] (Softness) Comparison with unfrozen cooked rice (Reference Example 1) which uses Akita Komachi rice as the raw material, has no additives for frozen cooked rice, and has been cooled to 25°C immediately after preparation. 5 points: Equivalent to Reference Example 1, with a very pleasant softness. 4 points: Slightly inferior to example 1, but still has a moderate level of softness. 3 points: Inferior to Reference Example 1; slightly harder or slightly softer, but still at a level that does not affect product quality. 2 points: Worse than example 1; too hard or too soft. 1 point: Significantly worse than Reference Example 1, clearly too hard or clearly too soft.

[0065] (Stickiness) Comparison with unfrozen cooked rice (Reference Example 1) which uses Akita Komachi rice as the raw material, has no additives for frozen cooked rice, and has been cooled to 25°C immediately after preparation. 5 points: Equivalent to Reference Example 1, with a very desirable level of viscosity. 4 points: Slightly inferior to Reference Example 1, but with a moderate level of stickiness. 3 points: It is inferior to Reference Example 1 and slightly less sticky, but it is still at an acceptable level in terms of product quality. 2 points: Worse than Reference Example 1, less sticky, and slightly dry. 1 point: Significantly worse than example 1, clearly lacking stickiness and feeling dry.

[0066] (Grain Texture) Comparison with unfrozen cooked rice (Reference Example 1) made using Akita Komachi rice as the raw material, without any additives for frozen cooked rice, and cooled to 25°C immediately after preparation. 5 points: Equivalent to Reference Example 1, with a noticeable grainy texture. 4 points: Slightly inferior to Reference Example 1, but still has a moderate amount of texture. 3 points: It is inferior to Reference Example 1, and has slightly less texture, but it is still at an acceptable level in terms of product quality. Points 2: Worse than Reference Example 1, with less distinct grain texture and noticeable sticking between grains. 1 point: This is significantly worse than Reference Example 1, clearly lacking individual grains and showing signs of clumping together.

[0067] (comprehensive evaluation) An overall evaluation was conducted based on the results of the softness, stickiness, and grain texture assessments. The evaluation criteria were as follows: A: Products that meet the criteria of having a score of 4.0 or higher and 5.0 or lower in terms of softness, stickiness, and graininess. B: The softness, stickiness, and graininess ratings are all between 3.5 and 5.0, and at least one item is between 3.5 and 4.0. C: The softness, stickiness, and graininess ratings are all between 3.0 and 5.0, and there is at least one item that is between 3.0 and 3.5. D: The softness, stickiness, and graininess ratings are all between 2.0 and 5.0, and there is at least one item that is between 2.0 and 3.0. E: Products with at least one score below 2.0 in the evaluation of softness, stickiness, and graininess.

[0068] (Manufacturing Example 1) Production of extracts derived from basidiomycetes 9.1 parts by weight (wet weight) of commercially available enoki mushrooms were extracted with 90.9 parts by weight of a 15 wt% potassium hydroxide aqueous solution at 100°C for 2 hours. After filtering using filter paper (Advantec Co., Ltd.), the recovered filtrate was concentrated under reduced pressure using an ultrafiltration concentrator (Advantec Co., Ltd., model number: UHP-150) to obtain approximately 48.5 parts by weight of concentrate. This concentrate was centrifuged at 10,000 × g for 10 minutes to collect the supernatant with a solid content of 1.5 mg / ml. This supernatant was used as the basidiomycete extract (enoki mushroom extract).

[0069] (Example 1) Preparation of frozen cooked rice According to Table 1, as a raw material for cooking rice, 0.14 parts by weight of basidiomycete extract (Production Example 1), 0.008 parts by weight of α-glycosyltransferase, 0.027 parts by weight of α-amylase, and 178 parts by weight of water were added to 100 parts by weight of pre-washed rice "Akita Komachi" as the raw material for cooking rice. After standing for 1 hour, the rice was cooked using an IH rice cooker. The cooked rice was molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated, and the results are shown in Table 1. The unit amount of each enzyme, the activity ratio, and the solid content of the extract in each example and reference example are as shown in Table 1.

[0070] [Table 1]

[0071] (Examples 2-6) Preparation of frozen cooked rice According to the formulations in Table 1, the α-glycosyltransferase (0.008 parts by weight) and α-amylase (0.027 parts by weight) in Example 1 were changed to 0.002 parts by weight and 0.0067 parts by weight (Example 2), 0.03 parts by weight and 0.10 parts by weight (Example 3), 0.003 parts by weight and 0.10 parts by weight (Example 4), 0.2 parts by weight and 0.067 parts by weight (Example 5), or 0.03 parts by weight and 0.001 parts by weight (Example 6), respectively. Except for these changes, the rice was cooked in the same manner as in Example 1, then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 1.

[0072] (Example 1) Preparation of cooked rice In Example 1, rice was cooked in the same manner as in Example 1, except that the basidiomycete extract, α-glycosyltransferase, and α-amylase were not added, and the amount of water was changed from 178 parts by weight to 150 parts by weight. After cooking, the cooked rice was cooled to 25°C, molded into 60g portions, and the results of the sensory evaluation are shown in Table 1 as Reference Example 1.

[0073] As is clear from Table 1, the rice used as a cooking ingredient containing 50 to 5000 units of α-glycosyltransferase and 1.5 to 150 units of α-amylase per 100g of raw rice, with an α-glycosyltransferase / α-amylase (enzyme activity ratio) in the range of 0.5 to 500, was cooked and then frozen (Examples 1 to 6). In all cases, the softness, stickiness, and grain texture of the rice after natural thawing were evaluated favorably.

[0074] (Comparative Examples 1-6) Preparation of Frozen Rice According to the formulations in Table 2, the α-glycosyltransferase (0.008 parts by weight) and α-amylase (0.027 parts by weight) in Example 1 were changed to 0.002 parts by weight and 0.0067 parts by weight (Comparative Example 1), 0.21 parts by weight and 0.067 parts by weight (Comparative Example 2), 0.002 parts by weight and 0.0005 parts by weight (Comparative Example 3), 0.03 parts by weight and 0.11 parts by weight (Comparative Example 4), 0.003 parts by weight and 0.1 parts by weight (Comparative Example 5), or 0.032 parts by weight and 0.001 parts by weight (Comparative Example 6), respectively. Except for these changes, the rice was cooked in the same manner as in Example 1, shaped, and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 2. The unit amounts, activity ratios, and solid content of the extracts for each comparative example are shown in Table 2.

[0075] [Table 2]

[0076] As is clear from Table 2, the frozen rice (Comparative Example 1) using a rice cooking ingredient with a low α-glycosyltransferase content of 38 units per 100g of raw rice showed poor evaluation of grain texture after natural thawing, resulting in an overall evaluation of D. The frozen rice (Comparative Example 2) using a rice cooking ingredient with a high α-glycosyltransferase content of 5250 units per 100g of raw rice showed poor evaluation of softness and grain texture after natural thawing, resulting in an overall evaluation of D. The frozen rice (Comparative Example 3) using a rice cooking ingredient with a low α-amylase content of 0.75 units per 100g of raw rice showed poor evaluation of stickiness and grain texture after natural thawing, resulting in an overall evaluation of D. The frozen rice (Comparative Example 4) using a rice cooking ingredient with a high α-amylase content of 165 units per 100g of raw rice showed poor evaluation of softness and grain texture after natural thawing, resulting in an overall evaluation of D. Frozen rice (Comparative Example 5) using rice for cooking with a low α-glycosyltransferase / α-amylase (enzyme activity ratio) of 0.42 in the raw rice showed poor evaluation of grain texture after natural thawing, resulting in an overall evaluation of D. Frozen rice (Comparative Example 6) using rice for cooking with a high α-glycosyltransferase / α-amylase (enzyme activity ratio) of 533 in the raw rice showed poor evaluation of stickiness after natural thawing, resulting in an overall evaluation of D.

[0077] (Comparative Example 7) Preparation of frozen cooked rice According to the formulation in Table 2, the α-glycosyltransferase in Example 1 was changed from 0.008 parts by weight to 0.3 parts by weight, and 0.027 parts by weight of α-amylase and 0.14 parts by weight of basidiomycete extract (Production Example 1) were omitted. Otherwise, the rice was cooked in the same manner as in Example 1, shaped, and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 2.

[0078] As is clear from Table 2, the frozen rice (Comparative Example 7) made using a rice cooking ingredient with a high amount of α-glycosyltransferase (7500 units) per 100g of raw rice, and without the addition of α-amylase and basidiomycete-derived extracts, had a poor evaluation of grain texture after natural thawing, resulting in an overall evaluation of D.

[0079] (Comparative Example 8) Preparation of frozen cooked rice Following the formulation in Table 2, the rice was cooked in the same manner as in Example 1, except that 0.027 parts by weight of α-amylase was omitted and 0.004 parts by weight of β-amylase was added instead. The cooked rice was then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 2.

[0080] As is clear from Table 2, the frozen rice (Comparative Example 8) made using a rice cooking ingredient that did not contain α-amylase but instead contained β-amylase, had a poor evaluation of the grain texture of the rice after natural thawing, and received an overall evaluation of D.

[0081] (Examples 7-8 and Comparative Examples 9-10) Preparation of frozen cooked rice According to the formulations in Table 3, the basidiomycete-derived extract (Production Example 1) in Example 1 was changed from 0.14 parts by weight to 0.02 parts by weight (Example 7), 2.0 parts by weight (Example 8), 0.014 parts by weight (Comparative Example 9), or 4.4 parts by weight (Comparative Example 10). Except for this change, the rice was cooked in the same manner as in Example 1, then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 3. The unit amounts of each enzyme, the activity ratio, and the solid content of the extract in each example and comparative example are as shown in Table 3.

[0082] [Table 3]

[0083] As is clear from Table 3, frozen rice (Examples 1, 7-8) using rice cooking ingredients with a solid content in the basidiomycete extract in the range of 0.00003 to 0.003 parts by weight per 100 parts by weight of raw rice all received good evaluations of softness, stickiness, and grain texture after natural thawing. On the other hand, frozen rice (Comparative Example 9) using rice cooking ingredients with a low solid content of 0.000021 parts by weight in the basidiomycete extract per 100 parts by weight of raw rice received poor evaluations of stickiness and grain texture after natural thawing, resulting in an overall evaluation of D. Furthermore, frozen rice (Comparative Example 10) using rice cooking ingredients with a high solid content of 0.0066 parts by weight in the basidiomycete extract per 100 parts by weight of raw rice received poor evaluations of softness after natural thawing, resulting in an overall evaluation of D.

[0084] (Comparative Example 11) Preparation of frozen cooked rice Following the formulation in Table 3, the α-glycosyltransferase (0.008 parts by weight) and α-amylase (0.027 parts by weight) from Example 1 were omitted. The basidiomycete extract (Production Example 1) was changed from 0.14 parts by weight to 0.10 parts by weight, and the added water (178 parts by weight) was changed to 150 parts by weight. The addition of 3.0 parts by weight of trehalose was also changed. Otherwise, the rice was cooked in the same manner as in Example 1, shaped, and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 3.

[0085] As is clear from Table 3, the frozen rice (Comparative Example 11) prepared using rice cooking ingredients that did not contain α-glycosyltransferase and α-amylase, but instead contained trehalose, received a poor evaluation of softness and stickiness after natural thawing, resulting in an overall evaluation of D.

[0086] (Example 12) Preparation of frozen cooked rice Following the formulations in Table 4, the rice was cooked in the same manner as in Example 1, except that 0.007 parts by weight of HM pectin was added. The cooked rice was then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 4. The unit amounts of each enzyme, the activity ratio, and the solid content of the extract in each example and comparative example are shown in Table 4.

[0087] [Table 4]

[0088] As is clear from Table 4, frozen cooked rice (Example 12) using a rice cooking ingredient with an HM pectin content in the range of 0.001 to 0.1 parts by weight per 100 parts by weight of raw rice showed good evaluations of softness, stickiness, and grain texture after natural thawing. In particular, it showed superior evaluations of softness and stickiness after natural thawing compared to frozen cooked rice (Example 1) without added HM pectin.

[0089] (Comparative Example 12) Preparation of frozen cooked rice Following the formulation in Table 4, the rice was cooked in the same manner as in Example 1, except that the basidiomycete extract (Production Example 1), 0.008 parts by weight of α-glycosyltransferase, and α-amylase from Example 1 were not added, the amount of added water was changed from 178 parts by weight to 190 parts by weight, and 0.67 parts by weight of HM pectin was added. The cooked rice was then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated, and the results are shown in Table 4.

[0090] As is clear from Table 4, the frozen cooked rice (Comparative Example 12) made using a rice cooking raw material with a high HM pectin content of 0.67 parts by weight per 100 parts by weight of raw rice, without the addition of basidiomycete extract (Production Example 1), α-glycosyltransferase, and α-amylase, showed poor evaluation of stickiness and grain texture after natural thawing, resulting in an overall evaluation of E.

[0091] (Examples 13-14 and Comparative Examples 13-14) Preparation of frozen cooked rice According to the formulations in Table 4, the rice was cooked in the same manner as in Example 1, except that the amount of added water (178 parts by weight) in Example 1 was changed to 150 parts by weight (Example 13), 190 parts by weight (Example 14), 145 parts by weight (Comparative Example 13), or 200 parts by weight (Comparative Example 14). After cooking, the resulting cooked rice was shaped and frozen to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 4.

[0092] As is clear from Table 4, frozen cooked rice (Examples 1, 12-14) using rice cooking ingredients with a water content in the range of 150-190 parts by weight per 100 parts by weight of raw rice showed good evaluations of softness, stickiness, and grain texture after natural thawing. On the other hand, frozen cooked rice (Comparative Example 13) using rice cooking ingredients with a low water content of 145 parts by weight per 100 parts by weight of raw rice showed poor evaluations of softness and stickiness after natural thawing, resulting in an overall evaluation of D. Furthermore, frozen cooked rice (Comparative Example 14) using rice cooking ingredients with a high water content of 200 parts by weight per 100 parts by weight of raw rice also showed poor evaluations of softness and grain texture after natural thawing, resulting in an overall evaluation of D.

[0093] (Example 15) Preparation of an additive for frozen cooked rice According to Table 5, 92.8 parts by weight of sorbitol solution heated to 40°C was stirred using a chemical stirrer (Tokyo Rikagaku Kiki Co., Ltd., "Model No.: ZZ-1020") for 41.7 seconds. -1 While stirring, 0.3 parts by weight of α-glycosyltransferase, 1.0 part by weight of α-amylase, 5.4 parts by weight of basidiomycete extract (Production Example 1), 0.25 parts by weight of HM pectin, and 0.25 parts by weight of xanthan gum were added and dissolved to obtain a frozen rice improver. The solid content of the basidiomycete extract, the content of α-glycosyltransferase and α-amylase in the obtained frozen rice improver are shown in Table 5. The unit amount of each enzyme, the activity ratio, and the solid content of the extract in each example are as shown in Table 5.

[0094] [Table 5]

[0095] (Example 16) Preparation of an additive for frozen cooked rice A frozen rice improver was obtained in the same manner as in Example 15, except that 0.3 parts by weight of α-glycosyltransferase was changed to 6.6 parts by weight, 1.0 part by weight of α-amylase was changed to 0.22 parts by weight, 5.4 parts by weight of basidiomycete-derived extract (Production Example 1) was changed to 13.6 parts by weight, 0.25 parts by weight of HM pectin was changed to 0.5 parts by weight, and 92.8 parts by weight of sorbitol was changed to 78.8 parts by weight, according to the formulation in Table 5. The solid content of the basidiomycete-derived extract, the content of α-glycosyltransferase and α-amylase in the obtained frozen rice improver, as well as the α-glycosyltransferase / α-amylase (enzyme activity ratio) are shown in Table 5.

[0096] (Example 17) Preparation of an additive for frozen rice A frozen rice improver was obtained in the same manner as in Example 15, except that 0.3 parts by weight of α-glycosyltransferase was changed to 0.1 parts by weight, 1.0 part by weight of α-amylase was changed to 3.33 parts by weight, and 92.8 parts by weight of sorbitol was changed to 90.67 parts by weight, according to the formulation in Table 5. The solid content of the basidiomycete-derived extract, the content of α-glycosyltransferase and α-amylase in the obtained frozen rice improver, and the α-glycosyltransferase / α-amylase (enzyme activity ratio) are shown in Table 5.

[0097] (Example 18) Preparation of an additive for frozen cooked rice According to the formulation in Table 5, add 28.73 parts by weight of water to 49.6 parts by weight of sorbitol solution heated to 40°C, and stir using a chemical stirrer (Tokyo Rikagaku Kiki Co., Ltd., "Model No.: ZZ-1020") for 41.7 seconds. -1While stirring, 0.66 parts by weight of α-glycosyltransferase, 0.11 parts by weight of α-amylase, 5.4 parts by weight of basidiomycete extract (production example 1), 0.25 parts by weight of HM pectin, and 0.25 parts by weight of xanthan gum were added and dissolved. 2.5 parts by weight of sucrose fatty acid ester were added to this mixture, and the temperature was raised to 80°C while stirring. 10.0 parts by weight of glycerin fatty acid ester and 2.5 parts by weight of citrate monoglyceride were added and dissolved. The resulting solution was homogenized using a high-speed emulsifier / disperser (Primix Co., Ltd., "Model No.: Homomixer MARK II") while being cooled to 55°C. This solution was then kept warm in a 38°C constant temperature bath for 16 hours to obtain a rice improver for frozen rice. Table 5 shows the solid content, α-glycosyltransferase, and α-amylase content of the basidiomycete-derived extract in the obtained frozen rice improver, as well as the α-glycosyltransferase / α-amylase (enzyme activity ratio).

[0098] (Example 19) Preparation of frozen cooked rice According to Table 6, as a raw material for cooking rice, 2.8 parts by weight of the frozen rice improver from Example 15 and 178 parts by weight of water were added to 100 parts by weight of pre-washed rice "Akita Komachi" as the raw material for cooking rice. After standing for 1 hour, the rice was cooked using an IH rice cooker. The cooked rice was molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated, and the results are shown in Table 6. The unit amount of each enzyme, activity ratio, solid content of the extract, and amount of HM pectin in each example are as shown in Table 6.

[0099] [Table 6]

[0100] (Examples 20-22) Preparation of frozen cooked rice Frozen rice was obtained by cooking rice in the same manner as in Example 19, except that 2.8 parts by weight of the frozen rice improver in Example 19 (Example 15) was replaced with 1.0 part by weight of the frozen rice improver in Example 16 (Example 20), 2.0 parts by weight of the frozen rice improver in Example 17 (Example 21), or 2.8 parts by weight of the frozen rice improver in Example 18 (Example 22), according to Table 6. The cooked rice was then shaped and frozen to obtain frozen rice. The obtained frozen rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated, and the results are shown in Table 6.

[0101] As is clear from Table 6, frozen cooked rice (Examples 19-22) using a rice cooking ingredient in which the solid content of the basidiomycete-derived extract was in the range of 0.00003 to 0.003 parts by weight per 100 parts by weight of raw rice, and which contained 50 to 5000 units of α-glycosyltransferase and 1.5 to 150 units of α-amylase per 100g of raw rice, with an α-glycosyltransferase / α-amylase (enzyme activity ratio) in the range of 0.5 to 500, all showed good evaluations of softness, stickiness, and grain texture after natural thawing.

[0102] (Example 23) Preparation of frozen cooked rice According to Table 7, rice was cooked in the same manner as in Example 19, except that the raw material rice, pre-washed rice "Akitakomachi," was changed to pre-washed rice "Koshihikari." After cooking, the cooked rice was molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated, and the results are shown in Table 7. The unit amount of each enzyme, activity ratio, solid content of the extract, and amount of HM pectin in each example, comparative example, and reference example are shown in Table 7.

[0103] [Table 7]

[0104] (Example 2) Preparation of cooked rice In Example 23, the rice was cooked in the same manner as in Example 23, except that 2.8 parts by weight of the frozen rice improver from Example 15 was not added, and the water was changed from 178 parts by weight to 150 parts by weight. After cooking, the cooked rice was cooled to 25°C, molded into 60g portions, and the results of the sensory evaluation are shown in Table 7 as Reference Example 2.

[0105] (Example 24) Preparation of frozen cooked rice In accordance with Table 7, the raw rice was changed from pre-washed "Akitakomachi" to "Kiyonishiki," and after washing it three times under running water, water was added to make a total of 178 parts by weight of added water. Otherwise, the rice was cooked in the same manner as in Example 19. The cooked rice was then molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 7.

[0106] (Example 3) Preparation of cooked rice In Example 24, the rice was cooked in the same manner as in Example 24, except that 2.8 parts by weight of the frozen rice improver from Example 15 was not added, and the water was changed from 178 parts by weight to 150 parts by weight. After cooking, the rice was cooled to 25°C, molded into 60g portions, and the results of the sensory evaluation are shown in Table 7 as Reference Example 3.

[0107] (Example 25) Preparation of frozen cooked rice According to Table 7, the raw rice was changed from pre-washed "Akitakomachi" to "Nihonbare," and after washing it three times under running water, water was added to make a total of 178 parts by weight of added water. Otherwise, the rice was cooked in the same manner as in Example 19. The cooked rice was then molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 7.

[0108] (Reference example 4) Preparation of cooked rice In Example 25, the rice was cooked in the same manner as in Example 25, except that 2.8 parts by weight of the frozen rice improver used in Example 15 was not added, and the water was changed from 178 parts by weight to 150 parts by weight. After cooking, the cooked rice was cooled to 25°C, molded into 60g portions, and the results of the sensory evaluation are shown in Table 7 as Reference Example 4.

[0109] (Comparative Example 15) Preparation of frozen cooked rice According to Table 7, the raw rice was changed from pre-washed rice "Akitakomachi" to "Hoshiyutaka," and after washing it three times under running water, water was added to make a total of 178 parts by weight of added water. Otherwise, the rice was cooked in the same manner as in Example 19, and the cooked rice was molded into 60g portions and held in a rapid freezing device at -30°C for 30 minutes to obtain frozen cooked rice. The obtained frozen cooked rice was stored at -20°C for 7 days, then naturally thawed (at 25°C for 4 hours) and evaluated. The results are shown in Table 7.

[0110] (Reference example 5) Preparation of cooked rice In Comparative Example 15, the rice was cooked in the same manner as in Comparative Example 15, except that 2.8 parts by weight of the frozen rice improver used in Example 15 was not added, and the water was changed from 178 parts by weight to 150 parts by weight. After cooking, the cooked rice was cooled to 25°C, molded into 60g portions, and the results of the sensory evaluation are shown in Table 7 as Reference Example 5.

[0111] As is clear from Table 7, frozen cooked rice (Examples 19, 23-25) using raw rice that met conditions (A) and (B) for amylose content [X] and moisture content [Y] showed good evaluations of softness, stickiness, and grain texture after natural thawing. On the other hand, frozen cooked rice (Comparative Example 15) using rice with a high amylose content [X] of 25.5% by weight showed poor evaluations of stickiness and grain texture after natural thawing, resulting in an overall evaluation of D.

Claims

1. It is an additive for frozen cooked rice, The raw rice for the aforementioned frozen cooked rice is rice that satisfies the following conditions (A) or (B) in terms of amylose content [X] (weight%) and moisture content [Y] (weight%). In the entirety of the aforementioned frozen rice improver, an extract derived from enoki mushrooms is included in an amount of 0.003 to 0.1% by weight (on a solid content basis), and The aforementioned improving agent contains 5,000 to 166,500 units of α-glycosyltransferase and 150 to 5,000 units of α-amylase per 100 g. The α-glycosyltransferase / α-amylase (enzyme activity ratio) is 0.5 to 500. The aforementioned extract is a rice improver for frozen rice intended for consumption after natural thawing. It is obtained by extracting a mixture of enoki mushrooms (wet weight) / water, alkaline water, and ethanol in a total weight ratio of 0.05 to 10 at 40 to 160°C for 0.1 to 12 hours, and then removing the extract residue derived from enoki mushrooms. [Condition (A)] 11.5 ≤ X < 19 and 11 ≤ Y < 7.0 + 8.5 × {1 - [(X - 19.0) / 8.5] ２ } １／２ [Condition (B)] 19 ≤ X ≤ 25 and 11 ≤ Y ≤ 15.5

2. The frozen rice improver according to claim 1, wherein the entire frozen rice improver contains 0.1 to 3.3% by weight of HM pectin.

3. This is frozen cooked rice, which is made by cooking the raw materials for cooking rice and then freezing it. The aforementioned rice cooking ingredients contain raw rice, solids contained in the extract derived from enoki mushrooms, water, α-glycosyltransferase, and α-amylase. For every 100 parts by weight of the aforementioned raw rice, the solid content of the enoki mushroom extract is 0.00003 to 0.003 parts by weight, and water is 150 to 190 parts by weight. Furthermore, per 100g of the raw rice, the amount of α-glycosyltransferase is 50 to 5000 units, and the amount of α-amylase is 1.5 to 150 units. The α-glycosyltransferase / α-amylase (enzyme activity ratio) is 0.5 to 500. The aforementioned raw rice is rice whose amylose content [X] (weight %) and moisture content [Y] (weight %) satisfy the following conditions (A) or (B): The aforementioned extract is a frozen rice product intended for consumption after natural thawing. The extract is obtained by extracting a mixture in which the total amount (weight ratio) of enoki mushrooms (wet weight) / water, alkaline water, and ethanol is 0.05 to 10, at 40 to 160°C for 0.1 to 12 hours, and then removing the extract residue derived from enoki mushrooms. [Condition (A)] 11.5 ≤ X < 19 and 11 ≤ Y < 7.0 + 8.5 × {1 - [(X - 19.0) / 8.5] ２ } １／２ [Condition (B)] 19 ≤ X ≤ 25 and 11 ≤ Y ≤ 15.5

4. The aforementioned rice cooking ingredients contain 0.001 to 0.1 parts by weight of HM pectin per 100 parts by weight of the aforementioned raw rice, wherein the frozen cooked rice for consumption after natural thawing is as described in claim 3.

5. Rice obtained by naturally thawing the frozen rice according to claim 3 or 4.

6. A method for manufacturing frozen cooked rice to be eaten after natural thawing, The ingredients for cooking rice are cooked and then frozen. The aforementioned rice cooking ingredients include raw rice, solids contained in the extract derived from enoki mushrooms, water, α-glycosyltransferase, and α-amylase. With respect to 100 parts by weight of the raw rice, the solid content of the extract derived from the enoki mushroom is 0.00003 to 0.003 parts by weight, and the water is 150 to 190 parts by weight. The α-glycosyltransferase and α-amylase are mixed in such a way that 50 to 5000 units and 1.5 to 150 units respectively are present in 100 g of the raw rice, and the α-glycosyltransferase / α-amylase (enzyme activity ratio) is 0.5 to 500. The aforementioned raw rice is rice whose amylose content [X] (weight %) and moisture content [Y] (weight %) satisfy the following conditions (A) or (B): The aforementioned extract is obtained by extracting a mixture in which the total amount (weight ratio) of enoki mushrooms (wet weight) / water, alkaline water, and ethanol is 0.05 to 10 at 40 to 160°C for 0.1 to 12 hours, after which the extract residue derived from enoki mushrooms is removed, in a method for producing frozen rice for consumption after natural thawing. [Condition (A)] 11.5 ≤ X < 19 and 11 ≤ Y < 7.0 + 8.5 × {1 - [(X - 19.0) / 8.5] ２ } １／２ [Condition (B)] 19 ≤ X ≤ 25 and 11 ≤ Y ≤ 15.5

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