WO2023068205A1

WO2023068205A1 - Production method of indigestible rice, and indigestible rice

Info

Publication number: WO2023068205A1
Application number: PCT/JP2022/038435
Authority: WO
Inventors: 幸春小川; スカニアツェンタン; 一鏑蔡; 亦辰丁
Original assignee: 国立大学法人千葉大学
Priority date: 2021-10-19
Filing date: 2022-10-14
Publication date: 2023-04-27

Abstract

The present invention addresses the problem of providing a novel production method of indigestible rice and indigestible rice. As a means for solving the problem, provided are: a production method of indigestible rice characterized by comprising a heat treatment step for subjecting raw unhulled rice to a heat treatment under one or more of the following conditions (1) to (3); indigestible rice produced through this heat treatment step; indigestible rice showing a digestion rate constant, which is evaluated by a simulated digestion test, decreased by 10% or more compared with untreated rice with no heat treatment; and indigestible rice showing a indigestible starch content increased by 50% or more compared with untreated rice with no heat treatment. (1) Exposing to a high humidity atmosphere of at least 90% RH at 60-80°C inclusive for 2-24 hours inclusive. (2) Exposing in warm water at 60-80°C inclusive for 2-24 hours inclusive. (3) Heating by microwave to 60-100°C inclusive.

Description

Method for producing resistant rice, and resistant rice

The present invention relates to a method for producing resistant rice, and resistant rice.

Foods containing carbohydrates, such as bread, noodles, and rice, are digested and absorbed in the small intestine after ingestion, causing a rapid rise in blood sugar levels. It has been pointed out that this reaction is deeply related to the development of lifestyle-related diseases such as type 2 diabetes and hyperlipidemia. Worldwide, the number of people with diabetes will increase from 171 million in 2000 to 366 million in 2030, and the number of people with hyperlipidemia will increase from 972 million in 2000 to 15 in 2025. It is projected to increase to 600 million. Therefore, there is a demand for foods in which the digestion and absorption of carbohydrates are slow.

Unlike bread and noodles that are made from wheat flour that has lost its seed structure, cooked rice maintains its structure as a seed, so the increase in blood sugar level is mild compared to bread and noodles. However, cooked rice is a staple food in many Asian countries, and rice as a staple food is consumed in a large amount per meal (1 slice of bread: about 60 g (sugar 27 g), 1 bowl of rice: about 140 g (sugar Quality 55g)), the absolute amount of absorbed carbohydrates tends to increase. In addition, in the Asian region, the number of patients with lifestyle-related diseases such as diabetes is increasing as the standard of living improves. Therefore, there is a demand for cooked rice foods in which the digestion and absorption of carbohydrates are slow.

As a method for suppressing the digestibility of carbohydrates in cooked rice, a method using mutant rice with a high content of indigestible starch has been proposed. , Patent Document 2 describes rice cooked by immersing mutant rice in a suspension of unsalted miso and then high-pressure treatment at 1000 atmospheres or more, and Patent Document 3 describes amylose synthase I and amylopectin branching enzymes. Mutant rice has been proposed that is deficient indigestible.
The use of mutant rice is based on changes in the biological characteristics of the plant species rice. There are a certain number of people who feel aversion to foods that use genetically modified ingredients, and development of mutant rice as a food depends on social tolerance. In addition, since this mutant rice is inevitably inferior in taste, in Patent Document 1, the amount of water added when cooking rice is doubled or more than usual, and in Patent Document 2, the amino acids of miso give flavor, and furthermore, the pressure is 1000 atmospheres or more. The taste is improved by breaking the cell walls of the rice by adding pressure. In addition, the mutated rice of Patent Document 3 becomes cooked rice that feels sticky like glutinous rice after cooking.

Patent Documents 4 to 8 propose cooked rice with reduced digestibility by adding indigestible polysaccharides such as indigestible dextrin, polysaccharides, and konnyaku grains during cooking. These are products in which a portion of rice is replaced with indigestible polysaccharides, and since indigestible polysaccharides are more expensive than rice, it is a heavy financial burden to continuously consume them.
Patent document 9 proposes a method for producing slow-digesting starch recombinant instant rice by combining protease hydrolysis, acetic anhydride esterification, and extruder extrusion compression molding technology using rice flour after solid amorphization treatment as a raw material. there is This method is a method of producing grain-like starch by extrusion compression molding with an extruder, and the product produced is different from rice.

In Patent Document 10, uncooked rice is immersed in a preparation liquid containing lactic acid bacteria having a high ability to produce polysaccharide thickeners, polysaccharide thickeners are produced in the rice tissue structure, and then edible rice is sealed. A method for producing diet rice by moist heat heating has been proposed. Moreover, Patent Documents 11 to 13 describe a method for producing low-calorie cooked rice in which uncooked rice treated by the same method as in Patent Document 10 is filled in a packaging pack and heated with moist heat to convert part of the starch into resistant starch. is proposed.
The methods described in Patent Documents 10 to 13 may spoil if bacteria are mixed (contamination) during fermentation with lactic acid bacteria, so sterilization of the equipment used for fermentation and contamination with bacteria floating in the air. Therefore, the environmental management of the manufacturing process becomes complicated. In addition, after being immersed in the lactic acid bacteria solution, rice containing a large amount of moisture with lactic acid bacteria attached is handled, so that bacteria are likely to propagate in the subsequent manufacturing process, which poses a storage problem.

JP 2006-217813 A JP 2017-042089 A JP 2009-254265 A Japanese Patent Publication No. 2016-516443 JP 2017-066064 A JP 2017-143771 A JP 2008-206527 A JP-A-9-154507 Japanese Patent Publication No. 2020-530758 Japanese Patent Application Laid-Open No. 2004-154091 Japanese Patent Application Laid-Open No. 2003-210121 Japanese Patent Application Laid-Open No. 2004-298079 Japanese Patent Application Laid-Open No. 2003-102408

An object of the present invention is to provide a novel method for producing resistant rice and resistant rice.

Means for solving the problems of the present invention are as follows.
1. A method for producing indigestible rice, comprising a heat treatment step of subjecting uncooked rice to heat treatment under any one or more of the following conditions (1) to (3).
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
2. 1. Characterized in that the heat treatment step (1) or (2) is performed at 68° C. or lower. 3. The method for producing indigestible rice according to .
3. 1. The heat treatment step (2) is performed in hot water for 12 hours or less. or 2. 3. The method for producing indigestible rice according to .
4. 1. The heat treatment step (3) is performed at a temperature elevation rate of 0.5° C./second or more. 3. The method for producing indigestible rice according to .
5. An indigestible rice produced through a heat treatment step in which uncooked rice is subjected to a heat treatment under any one or more of the following conditions (1) to (3).
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
6. An indigestible rice characterized by having a digestion rate constant that is reduced by 10% or more as evaluated in a simulated digestion test as compared with untreated rice that has not been heat-treated.
7. A resistant rice characterized by having an amount of resistant starch increased by 50% or more compared to untreated rice that has not been heat-treated.

According to the production method of the present invention, resistant rice can be produced regardless of the rice variety. The production method of the present invention is the same as the conventional preparation method except that it includes a heat treatment step, and no special equipment is required for the heat treatment step. Therefore, the added value of resistance to digestion can be imparted to raw rice harvested from rice of any variety without making a large capital investment. The production method of the present invention is different from biological modification such as mutation and genetic recombination, and addition of other indigestible substances, and the indigestible rice obtained is rice itself, so it is socially acceptable. high and easily accepted by consumers. By utilizing the production method of the present invention, it becomes possible to take indigestible rice on a daily basis. qualitative improvement is achieved. By setting the heat treatment temperature to 68° C. or less, it is possible to produce indigestible rice that maintains its deliciousness as cooked rice. By heat-treating in hot water, it is possible to reduce the time required for heat-treating, energy costs, and the like.
Since the indigestible rice of the present invention has a slow digestion rate of starch and suppresses a rapid increase in postprandial blood sugar level, it can be suitably eaten by patients with diabetes and the like.

4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 1. FIG. Appearance of resistant rice after polishing obtained in Experiment 1. 4 is a graph showing hardness of resistant rice obtained in Experiment 1. FIG. 4 is a graph showing the adhesion of resistant rice obtained in Experiment 1. FIG. 4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 2. FIG. 4 is a graph showing hardness of resistant rice obtained in Experiment 2. FIG. 4 is a graph showing the adhesion of resistant rice obtained in Experiment 2. FIG. Appearance of resistant rice after polishing obtained in Experiment 3. 4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 3. FIG. 4 is a graph showing hardness of resistant rice obtained in Experiment 3. FIG. 4 is a graph showing the adhesion of resistant rice obtained in Experiment 3. FIG. 4 is a graph showing the relationship between the treatment time of resistant rice obtained by heat treatment at 65° C. in Experiment 4 and the amount of resistant starch. 4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained by wet heat treatment at 65° C. in Experiment 4. FIG. 10 is a graph showing evaluation results of a simulated digestion test of indigestible rice obtained by hot water treatment at 65° C. in Experiment 4. FIG. 5 is a graph showing the relationship between the treatment time of resistant rice obtained by heat treatment at 65° C. in Experiment 5 and the amount of resistant starch. 10 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained by wet heat treatment at 65° C. in Experiment 5. FIG. 10 is a graph showing evaluation results of a simulated digestion test of indigestible rice obtained by hot water treatment at 65° C. in Experiment 5. FIG. 10 is a graph showing the relationship between the treatment time of resistant rice obtained by heat treatment at 65° C. in Experiment 6 and the amount of resistant starch. 4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained by wet heat treatment in Experiment 6. FIG. 10 is a graph showing evaluation results of a simulated digestion test of indigestible rice obtained by hot water treatment in Experiment 6. FIG. 10 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 7. FIG. 10 is a graph showing evaluation results of a simulated digestion test when the indigestible rice obtained in Experiment 7 was slurried. 4 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 8. FIG. 10 is a graph showing evaluation results of a simulated digestion test of resistant rice obtained in Experiment 9. FIG. 10 is a graph showing changes in blood sugar level after eating in Experiment 10. FIG.

In the present specification, “raw rice” refers to rice before drying, “rice” refers to rice after drying, and “rice (including indigestible rice)” refers to brown rice from which the husks have been removed from rice and polished rice. means white rice.

The conventional preparation process of post-harvest rice is as follows.
Raw unhulled rice harvested and before drying has a moisture content of about 20 to 25%.
Raw unhulled rice is usually dried in the air at 30-35° C. until the moisture content reaches about 14.5-15% to obtain unhulled rice. Raw unhulled rice can be stored while maintaining its quality by drying it into unhulled rice.
Unhulled rice is stored as it is, and is hulled, polished, etc. just before shipment, and shipped as brown rice, white rice, or the like.

In the method for producing resistant rice of the present invention, raw rice is subjected to a heat treatment under any one or more of the following conditions (1) to (3), and dried after the heat treatment. It differs from the later preparation steps.
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
That is, the method for producing indigestible rice of the present invention is characterized by comprising a heat treatment step of subjecting uncooked rice to heat treatment under any one or more conditions of (1) to (3). .

In the present invention, the uncooked rice to be used is not particularly limited as long as it is an edible rice (Oryza sativa L.) seed, and any of japonica, indica, Javanica, etc. can be used. Among these, it is preferable to use the japonica variety, which contains a large amount of amylopectin and tends to increase the blood sugar level after eating. Incidentally, the uncooked rice used in the present invention is, of course, not limited in terms of its variety, place of production, and the like.

- Heat treatment step In the heat treatment step, the raw rice is subjected to heat treatment under any one or more of the following conditions (1) to (3).
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
Hereinafter, the treatment by (1) is also called wet heat treatment, the treatment by (2) is called hot water treatment, and the treatment by (3) is called microwave treatment. In the heat treatment step, one or more of wet heat treatment, hot water treatment, and microwave treatment can be performed. When performing two or more treatments, it is preferable to perform either wet heat treatment or warm water treatment, or both, after performing microwave treatment.

In the case of wet heat treatment or warm water treatment, the time required for heat treatment can be shortened by raising the heat treatment temperature. On the other hand, if the treatment temperature is high, the taste may deteriorate or the color may change. Therefore, when the indigestible rice produced by the present invention is eaten as it is as cooked rice, the treatment temperature is preferably 68° C. or lower, more preferably 65° C. or lower. However, when the indigestible rice produced by the present invention is eaten as flavored cooked rice such as fried rice or pilaf, the treatment temperature is high, for example, 68° C. °C.

In the case of wet heat treatment, the treatment time is preferably 4 hours or longer, more preferably 6 hours or longer. The humidity at this time is preferably 92% RH or higher, more preferably 94% RH or higher, and even more preferably 96% RH or higher.
When indigestible rice that has been subjected to moist heat treatment is eaten as cooked rice, it is preferable to treat it at 60°C to 67°C, 92% RH or more, 4 hours to 24 hours, 60°C to 65°C, 94°C. % RH or more and more preferably 6 hours or more and 12 hours or less.
When indigestible rice that has been subjected to moist heat treatment is eaten as flavored cooked rice, it is preferably treated at 70°C to 80°C, 92% RH or more, and 2 hours to 12 hours, and 75°C to 80°C. , more preferably 94% RH or more and 2 hours or more and 8 hours or less.

Since a liquid has a higher thermal conductivity than a gas, a liquid can give more heat than a gas at the same time. Also, although the cause is unknown, hot water treatment causes less change in taste and color compared to wet heat treatment. Therefore, in the case of hot water treatment, the treatment time is preferably 12 hours or less, more preferably 8 hours or less, and even more preferably 4 hours or less.
When indigestible rice treated with hot water is eaten as boiled rice or seasoned cooked rice, it is preferably treated at 60° C. or higher and 67° C. or lower for 8 hours or less, and 60° C. or higher and 65° C. or lower for 6 hours or less. is more preferable.

Microwave treatment is heating by a so-called microwave oven, in which water molecules are heated by oscillating them by irradiating them with microwaves. Microwave treatment can directly heat the moisture in raw rice by irradiating it with microwaves (moisture content of about 20 to 25%). , the time required for heat treatment can be greatly reduced. Microwave-treated indigestible rice is less likely to change in taste and color compared to wet-heat-treated or warm-water-treated indigestible rice. It is presumed that this is because the enzyme activity can be rapidly deactivated. Although the treatment temperature of the microwave treatment is not particularly limited, the treatment temperature is preferably 95° C. or lower, more preferably 90° C. or lower, and even more preferably 85° C. or lower from the viewpoint of energy cost. Moreover, the lower limit of the treatment temperature is preferably 65° C. or higher.
In the microwave treatment, it is preferable to raise the temperature quickly from the viewpoint of improving the resistance to digestion. is more preferably 1.5° C./second or more. In addition, since the microwave treatment tends to cause temperature unevenness, it is preferable to use an apparatus equipped with a stirring function.

In the method for producing indigestible rice of the present invention, the preparation process such as drying after the heat treatment process can be carried out in the same way as before. However, since the moisture content of raw rice after wet heat treatment or hot water treatment is higher than before treatment, it is slowly dried until the moisture content reaches about 14.5 to 15% to prevent cracking during drying. drying at 20 to 35° C. for 8 hours or more is preferable, drying is more preferably drying for 16 hours or more, and drying for 20 hours or more is even more preferable. Moreover, in the case of microwave treatment, drying can be performed under the same drying conditions as in the past.

- Indigestible rice The indigestible rice of the present invention can be obtained by subjecting uncooked rice to heat treatment under any one or more of the following conditions (1) to (3).
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
Since rice is an agricultural product, the ratio and molecular weight of amylose/amylopectin in the starch, the ratio and thickness of cellulose/hemicellulose/pectin in the cell wall, the moisture content, and the content of trace components such as proteins, vitamins, and inorganic components. etc. have variations. It is speculated that the heat treatment process causes at least the crystallization of starch and denaturation of the cell wall, resulting in a change to resistant rice. Have difficulty.

The indigestible rice of the present invention is digested more slowly and less easily than untreated rice that has not undergone a heat treatment step. In the resistant rice of the present invention, the starch digestion rate constant (min ⁻¹ ) evaluated in a simulated digestion test system is preferably 10% or more, and preferably 15% or more, lower than that of the untreated rice. more preferred. In addition, the resistant rice of the present invention preferably has an amount of resistant starch that is increased by 50% or more, more preferably by 100% or more, compared to the untreated rice.
The starch digestion rate constant of the resistant rice of the present invention is preferably 0.008 (min ^-1 ) or less, more preferably 0.007 (min ^-1 ) or less, and more preferably 0.0065 (min -1 ) or less. min ⁻¹ ) or less.

- Moisture content measurement method The moisture content of the polished rice grain sample was measured using a heat drying moisture meter (MX-50, manufactured by A&D Co., Ltd.).

・Crude protein determination method The crude protein amount of the polished rice grain sample was obtained by coarsely pulverizing with a mixer and then further pulverizing with an electric stone mill to a particle size of 50 µm or less. manufactured by Yanako). Using hippuric acid as a standard nitrogen substance, the resulting nitrogen content was multiplied by the nitrogen-to-protein conversion factor of 5.95 to quantify the crude protein content.
· Polished rice grain surface color measurement method The color value of the polished rice grain surface was evaluated by the CIELAB color system measurement mode of a spectrophotometer (CM-600d, manufactured by Konica Minolta). A petri dish having a diameter of 8 cm and a height of 1 cm was filled with a sufficient amount of the polished rice grain sample, and three points were randomly selected to measure the L ^* , a ^* , and b ^* values, and the average value was obtained. The whiteness (WI) was calculated using the following formula from the measured values obtained.
WI = 100 - ((100 - L ^* ) ² + (a ^*2 ) + (b ^*2 )) ^1/2

・ Rice cooking method Distilled water was added to 50 g of a sample of polished rice grains so that the ratio of rice: distilled water was 1:1.5 (w / v), and a simple heating type small electric rice cooker (mini cooker SR- MC03, manufactured by Panasonic Corporation) was used to cook rice. After the completion of rice cooking, the cooked rice was immediately transferred to a petri dish, sealed with plastic wrap, and allowed to stand in an incubator set at 30°C for 30 minutes. Subsequently, physical properties and digestibility were measured.

・Texture measurement method The hardness and adhesiveness of the cooked rice grain sample were measured using a creep meter (RE2, manufactured by Yamaden Co., Ltd.) and attached analysis software (texture analysis, TAS-3305 (W), manufactured by Yamaden Co., Ltd.). .
The cooked rice grains after being cooked and allowed to stand were placed on a measurement stage one by one and compressed in the short axis direction of the grains. The distance from the measurement stage to the rice grain surface is the thickness of the rice grain, the maximum load when the compression ratio reaches 90% is the hardness, and the area value obtained from the negative load and the return distance when the return operation is performed from there is attached. sex. The plunger is made of fluororesin and is disk-shaped (Φ30mm), which is sufficiently larger than the grain of cooked rice. bottom.

・ Reagent, kit pepsin (P7000, porcine gastric mucosa, ≧250 U / mg, solid: manufactured by Sigma-Aldrich)
Pancreatin (hog pancreas, 4 x USP: manufactured by Sigma-Aldrich)
Invertase (from baker/s yeast, grade VII, ≧300 U/mg, solid: manufactured by Sigma-Aldrich)
Amyloglucosidase (3260 U/mL: manufactured by Megazyme International)
α-amylase (3000 U/mL, No. E-BSTAA: manufactured by Megazyme International)
Total starch assay kit (K-TSTA-50A/K-TSTA-100A 08/19: manufactured by Megazyme International)
Resistant Starch Assay Kit (K-RSTAR, manufactured by Megazyme International)
D-glucose assay kit (D-glucose assay kit, GOPOD format, K-GLUC 03/2010: manufactured by Megazyme International)

- Reagent preparation A simulated gastric fluid (SGF) was obtained by dissolving 0.12 g of pepsin in 25 mL of a 0.2% (w/v) sodium chloride aqueous solution.
Simulated pancreatic juice (SIF: A simulated intestinal fluid) was obtained.

Invertase and amyloglucosidase were added to 20 ml of potassium acetate buffer and stirred to obtain an invertase/amyloglucosidase solution.
0.05 g of pancreatin and 0.00375 g of invertase were mixed with 50 ml of 100 mM sodium acetate buffer of pH 5.0 and stirred for 5 minutes, then 1 ml of amyloglucosidase was added and stirred for another 15 minutes while warming to 37°C. A digestive enzyme solution for quantifying resistant starch was obtained.

- Measurement of total starch content Polished grains of white rice were coarsely pulverized with a mixer, and then pulverized to a particle size of 50 µm or less using an electric stone mill. The total starch content of the obtained powder was quantified according to the procedure described in the manual of the total starch assay kit.
50 mg of powder was weighed into a test tube, mixed with 10 ml of 100 ml sodium acetate buffer adjusted to pH 5.0, stirred with a vortex mixer for 5 seconds, then 0.1 ml of α-amylase was dispensed, stirred again for 3 seconds, Heated in boiling water for 15 minutes. After 2, 5, and 10 minutes from the start of heating, the mixture was temporarily removed from the boiling water and stirred with a vortex mixer. After 15 minutes, the mixture was taken out, stirred with a vortex mixer, and incubated in a water bath set at 50°C for 5 minutes. After that, 0.1 ml of amyloglucosidase was added, stirred with a vortex mixer for 3 seconds, and incubated again in a water bath at 50°C for 30 minutes.

After completion of the incubation, the test tube was taken out, heat was removed at room temperature for 10 minutes, and then centrifuged at 13000 rpm for 5 minutes in a centrifuge set at 10°C to obtain a supernatant. After diluting the supernatant with 10-fold volume of sodium acetate buffer, 0.1 ml was collected, 3 ml of GOPOD was added, and the mixture was incubated in a water bath at 50° C. for 20 minutes.
The absorbance of the sample solution after incubation was measured at a wavelength of 510 nm using a spectrophotometer. The total starch content was calculated by comparing the obtained absorbance with the absorbance of a standard solution in which 0.1 ml of D-glucose at a concentration of 1.0 mg/ml was added with 3 ml of GOPOD.

- Determination of amount of indigestible starch Polished white rice grains were coarsely pulverized with a mixer, and then pulverized to a particle size of 50 µm or less using an electric stone mill. The resulting powder was measured for the amount of resistant starch according to the procedure described in the manual of the resistant starch assay kit.
200 mg of sample powder was weighed into a test tube, 4 ml of 100 ml of sodium acetate buffer was added, and the mixture was stirred for 5 seconds with a vortex mixer and allowed to stand for 10 minutes. Then, it was stirred again with a vortex mixer and heated in boiling water for 20 minutes. After heating, the sample was placed in a water bath set at 37°C and allowed to stand until the temperature of the sample liquid reached 37°C.
To the sample cooled to 37°C, 1 ml of the digestive enzyme solution used for quantification of resistant starch was added, stirred for 5 seconds with a vortex mixer, and shaken in a shaking water bath at 37°C for 4 hours. After that, 3 ml of 95% (v/v) ethanol was added to the test tube to stop the digestion treatment, and the tube was stirred again with the vortex mixer.
The resulting sample was centrifuged at 4000 rpm for 10 minutes in a centrifuge set at 10°C. Thereafter, after collecting the supernatant, 3 ml of 50% (v/v) ethanol was added to the solid content, stirred with a vortex mixer, and centrifuged again. The same procedure was repeated three times to separate all non-resistant starch in the sample.

The solid content from which the non-resistant starch was separated was mixed with 1 ml of 1.7 M sodium hydroxide, and stirred at 750 rpm for 20 minutes in a vessel covered with ice using a stirrer. After 20 minutes, 4 ml of 1 M sodium acetate buffer adjusted to pH 3.8 was added, 50 μl of amyloglucosidase was added, and the mixture was further stirred for 2 minutes. Immediately thereafter, it was incubated in a water bath set at 50°C for 30 minutes. After 30 minutes, the test tube was taken out, stirred with a vortex mixer for 5 seconds, and centrifuged at 13000 rpm for 5 minutes in a centrifuge set at 10°C to obtain a supernatant. 10 µl of the supernatant was collected, dispensed into microplates, added with 300 µl of GOPOD, and incubated in a thermostat set at 50°C for 20 minutes.
Absorbance was then measured at a wavelength of 510 nm using a microplate reader. The amount of resistant starch (resistant starch) was calculated by comparing the obtained absorbance with the absorbance of a standard solution in which 300 μl of GOPOD was added to 10 μl of D-glucose at a concentration of 1.0 mg/ml.

・ In vitro simulated digestion test (rice cooking conditions, digestibility test procedure, conditions)
Weighed so that the total starch content of the cooked rice sample was equivalent to 6.80 g, put it in a polyethylene draining net, and placed it in a 500 ml double-tube reaction vessel set at 37 ° C. (Sansho, 82-3625, hereinafter , also referred to as a reaction vessel), and distilled water was added to prepare a total of 170 g.
A stirrer and a pH electrode were installed in the reaction vessel, and only the liquid portion was stirred at 350 rpm so that the stirrer did not come into contact with the sample.
The pH was adjusted to 1.2 and SGF was added to reproduce digestion conditions in the stomach. After 30 minutes, the pepsin was inactivated by adding an appropriate amount of aqueous sodium hydroxide. The pH was then brought to 6.8±0.02 and SIF was added to mimic digestion conditions in the small intestine.

・In vitro simulated digestion test (digestibility evaluation method)
After 5 and 30 minutes reproducing digestion conditions in the stomach and after 5, 10, 15, 30, 60, 90, 120, 150, 180 and 210 minutes reproducing digestion conditions in the small intestine, an appropriate amount of sample was taken out and centrifuged at 3600×g for 5 minutes, and the glucose concentration in the obtained supernatant was quantified by the method shown below.
0.5 ml of the invertase/amyloglucosidase solution was added to 0.1 ml of the supernatant and allowed to stand in a water bath set at 37° C. for 10 minutes. After that, 0.1 ml was collected, mixed with 3 ml of GOPOD, and allowed to stand in a water bath set at 50° C. for 20 minutes.
The absorbance of the resulting sample solution was measured using a spectrophotometer at a wavelength of 510 nm, and calibrated with a standard solution of 0.1 ml of D-glucose to which 3 ml of GOPOD was added to determine the glucose concentration in the sample solution.

The hydrolysis rate (digestibility) of starch contained in cooked rice was calculated using the following formula.
%S _H =S _h /S _i =0.9G _p /S _i
Here, % _SH is the starch hydrolysis rate (digestibility, %), _Sh is the amount of hydrolyzed starch (g), _Si is the initial amount of starch (g), _G is the amount of glucose produced ( g), 0.9 indicates the conversion factor of molecular weight of glucose units in starch/molecular weight of glucose (162/180).

The transition of the digestibility in the simulated digestion process in the small intestine is approximated using the following first-order reaction equation, and among the calculated constant terms, k is the digestion rate constant (min ^-1 ) and C∞ is the equilibrium digestibility (%). and
C=C∞(1-exp(-kt))
Here, C is the starch hydrolysis rate (%) at time t, and t is the time (min) when the sample was taken during the simulated digestion process in the small intestine.

(Experiment 1)
Post-harvest raw rice (Hinohikari from Hiroshima Prefecture, crude protein content 5.4% (d.b.), initial moisture content 25.8% (w.b.)) Heat treatment was performed by exposing to RH high humidity circulating aeration conditions for 4 hours or 24 hours.
After the treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, and polished (90% of the weight of unpolished rice) to obtain resistant rice. In addition, this was cooked to obtain indigestible cooked rice.

^The evaluation results of the simulated digestion test of the obtained boiled rice are shown in ^FIG . . In addition, the appearance of the indigestible rice after polishing is shown in FIG. 2, and the firmness and adhesiveness of the indigestible cooked rice are shown in FIGS. 3 and 4, respectively.

It was confirmed that the higher the heat treatment temperature and the longer the treatment time, the more resistant rice with reduced carbohydrate digestibility was obtained (Fig. 1, Table 1).
When wet heat treatment was performed at 80°C, 98% RH for 24 hours, the treated resistant rice turned brown (Fig. 2). Although this resistant rice turned brown, it was the most resistant to digestion. At the same time, since the hardness increased and the adhesiveness decreased, it can be suitably used for seasoned boiled rice such as fried rice and pilaf (Figs. 3 and 4).

(Experiment 2)
Post-harvest uncooked rice (Toyomeki produced in Chiba Prefecture, crude protein content 6.9% (d.b.), initial moisture content 19.7% (w.b.)) was heated at 60°C or 65°C, 98% Heat treatment was performed by exposure to RH for 12 hours or 18 hours under high-humidity circulating aeration conditions. After the treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, and polished (90% of the weight of unpolished rice) to obtain resistant rice. In addition, this was cooked to obtain indigestible cooked rice.

Table 2 shows the water content, total starch content, and resistant starch content of the resistant rice after milling, and Table 3 shows the surface color of the polished rice grains.
The evaluation results of the simulated digestion test of the obtained boiled rice are shown in FIG. 5, and the calculated equilibrium digestibility and digestion rate constant are shown in Table 4. Firmness and adhesiveness of the indigestible boiled rice are shown in FIGS. 6 and 7, respectively.

The higher the heat treatment temperature, the higher the amount of resistant starch (Table 2). On the other hand, whiteness (WI) (Table 3) and equilibrium digestibility (Table 4) decreased with longer treatment times. However, in the heat treatment by high-humidity circulating aeration, no statistical difference in the digestion rate constant was observed at the treatment temperature of 60° C. or 65° C. and the treatment time of 12 hours or 18 hours. However, the treatment at 60° C. reduced the average digestion rate constant by about 10%.
As described above, it was confirmed that even if the heating temperature is 60° C. or 65° C. and the treatment time is 12 hours or 18 hours, as in the case of Experiment 1, resistant rice with reduced carbohydrate digestibility can be obtained. (Fig. 5).
The hardness of the cooked rice grains did not change even after heat treatment at 60° C. or 65° C., 98% RH for 12 hours or 18 hours. On the other hand, when heat treatment at 60° C. was performed, the adhesiveness increased to about three times that of the control (FIGS. 6 and 7). However, even after heat treatment at 65°C, there was no difference in the adhesion of the control.

(Experiment 3)
Raw unhulled rice after harvest (Toyomeki produced in Chiba Prefecture, crude protein content 6.9% (d.b.), initial moisture content 19.7% (w.b.)) is soaked in warm water at 65°C for 2 hours. , immersed for 4 hours or 6 hours, and heat-treated. After the treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, and polished (90% of the weight of unpolished rice) to obtain resistant rice. In addition, this was cooked to obtain indigestible cooked rice.

Table 5 shows the water content, total starch content, and resistant starch content of the milled resistant rice, Table 6 shows the surface color of the polished rice grains, and FIG.
The results of simulated digestion of the obtained boiled rice are shown in FIG. 9, and the calculated equilibrium digestibility and digestion rate constant are shown in Table 7. Firmness and adhesiveness of the indigestible boiled rice are shown in FIGS. 10 and 11, respectively.

Under the immersion heat treatment conditions of 65°C, the whiteness was slightly decreased by the treatment (Table 6, Fig. 8), but the immersion treatment resulted in resistant rice with reduced carbohydrate digestibility regardless of the treatment time. (Fig. 9). By heat-treating with hot water, heat can be given more efficiently than with air, and thus resistant rice was obtained in a short period of time (Fig. 9, Table 5).
When the immersion treatment was performed at 65°C, the hardness of the indigestible cooked rice obtained by cooking the rice after the immersion treatment for 2 hours or 4 hours did not differ from that of the control. However, after soaking for 6 hours, the indigestible boiled rice showed an average increase of about 1.5 times and an increase in adhesion of about 3 times compared to the control (Figs. 10 and 11). On the other hand, the equilibrium digestibility showed a decrease of about 10% regardless of the treatment time of the immersion treatment. As for the digestion rate constant, although no statistical difference was confirmed, an average value of about 20% decrease was confirmed for the indigestible boiled rice soaked for 4 hours. Therefore, the immersion-treated indigestible cooked rice can be used as cooked rice with reduced carbohydrate digestibility while having substantially the same physical properties as ordinary white rice.

(Experiment 4)
Raw unhulled rice after harvest (Koshihikari from Chiba Prefecture, protein content 6.0% (d.b.), initial moisture content 21.9% (w.b.)) was heated to 98°C in a temperature environment of 65°C. The heat treatment was performed by exposing to high-humidity circulating aeration at % RH for 6, 12, 18, 24, and 48 hours, or immersing in hot water at 65° C. for 2, 4, 6, and 12 hours. After the treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, and polished (90% of the weight of unpolished rice) to obtain resistant rice. In addition, this was cooked to obtain indigestible cooked rice.

Fig. 12 shows changes in the amount of resistant starch in the resulting resistant cooked rice for each treatment time. Fig. 13 shows the evaluation results of carbohydrate digestibility by simulated digestion of indigestible boiled rice obtained by heat treatment by high-humidity circulating aeration at 65°C and 98% RH and heat treatment by immersion in hot water at 65°C. , 14 and Table 8 shows the equilibrium digestibility and digestion rate constants.

In the heat treatment by high-humidity circulating aeration, it was confirmed that the amount of resistant starch increased as the heating time increased (Fig. 12). On the other hand, in the heat treatment by immersion in warm water, no increase in the amount of resistant starch with heating time was confirmed (Fig. 12).
As a result of evaluating carbohydrate digestibility, no significant difference in equilibrium digestibility was confirmed (Figs. 13 and 14). However, the digestion rate constants tended to decrease with heat treatment (Table 8). However, the tendency was not a result that correlated with the heating time.

(Experiment 5)
Raw unhulled rice after harvesting (Chiba-produced Scutellariae, protein content 6.5% (d.b.), initial moisture content 21.2% (w.b.)) was treated at 65°C in a temperature environment of 98°C. The heat treatment was performed by exposing to high-humidity circulating aeration at % RH for 6, 12, 18, 24, and 48 hours, or immersing in hot water at 65° C. for 2, 4, 6, and 12 hours. After the treatment, the rice was dried under ventilation at 35°C and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.

Fig. 15 shows changes in the amount of resistant starch in the milled rice obtained by heat treatment at 65°C for each treatment time. Carbohydrate digestion by simulated digestion of indigestible cooked rice obtained by cooking polished rice obtained by heat treatment by high-humidity circulation aeration at 65°C and 98% RH and heat treatment by immersion in hot water at 65°C. Figures 16 and 17 show the sex evaluation results, and Table 9 shows the equilibrium digestibility and digestion rate constant.

As in Experiment 4, in the heat treatment by high-humidity circulating aeration, it was confirmed that the amount of resistant starch increased as the heating time increased (Fig. 15). On the other hand, in the heat treatment by immersion in warm water, no increase in the amount of resistant starch with heating time was confirmed (Fig. 15).
As a result of evaluating carbohydrate digestibility, no significant difference in equilibrium digestibility was confirmed (Figs. 16 and 17). However, the digestion rate constant of the indigestible boiled rice immersed in hot water tended to decrease with the immersion treatment time, except when immersed for 2 hours (Table 9).

(Experiment 6)
Raw unhulled rice after harvest (Koshihikari from Chiba Prefecture, protein content 7.6% (d.b.), initial moisture content 26.9% (w.b.)) was heated to 98°C in a temperature environment of 65°C. The heat treatment was performed by exposing to high-humidity circulating aeration at % RH for 6, 12, 18, 24, and 48 hours, or immersing in hot water for 2, 4, 6, and 12 hours. After the treatment, the rice was dried under ventilation at 35°C and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.

Fig. 18 shows changes in the amount of resistant starch in the resulting resistant cooked rice for each treatment time. 19 and 20 show the evaluation results of carbohydrate digestibility by simulated digestion of indigestible boiled rice obtained by wet heat treatment and hot water treatment, and Table 10 shows the equilibrium digestibility and digestion rate constant.

As in Experiment 4, the cultivar is Koshihikari, but the heat treatment is applied to fresh firs that have a relatively high initial moisture content when harvested. As in

Experiments

4 and 5, it was confirmed that the amount of resistant starch increased as the heating time of the heat treatment by high-humidity circulating ventilation increased (Fig. 18). On the other hand, in the heat treatment by immersion in hot water, no increase in the amount of resistant starch with heating time was confirmed (Fig. 18).
Similar to

Experiments

4 and 5, no significant difference in equilibrium digestibility was confirmed in the carbohydrate digestibility evaluation results (Figs. 19 and 20). However, the digestion rate constant of the indigestible boiled rice immersed in hot water tended to decrease to about 1/2 times that of the control when immersed for 6 hours (Table 10).

(Experiment 7)
Raw unhulled rice after harvest (Hinohikari from Hiroshima Prefecture, protein content 5.4% (d.b.), initial moisture content 25.8% (w.b.)) was soaked in hot water at a temperature of 65 ° C. for 2 hours or 4 hours, followed by heat treatment. After the treatment, the rice was dried under ventilation at 35°C and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.

Fig. 21 shows the evaluation results of carbohydrate digestibility by a simulated digestion test of the obtained indigestible cooked rice. In addition, a simulated digestion test was similarly performed on the rice grains of this indigestible cooked rice that were made into a slurry with a mixer. The results are shown in FIG. Table 11 shows the amount of resistant starch, equilibrium digestibility and digestion rate constant.

By heat-treating with hot water, the amount of heat can be given more efficiently than with air, and thus indigestible rice was obtained in a short period of time (Fig. 21). It was confirmed that the longer the treatment time of warm water, the more the indigestibility improved, as with the hot and moist air.
Even in the form of slurry, the indigestible rice was superior to the control in digestibility (Fig. 22). From this, it was suggested that the heat treatment in which the starch was exposed to warm water changed the crystal structure or cell structure of the starch, which hindered the penetration of the digestive fluid. However, in the case of slurry, the resistant rice heat-treated for 2 hours is superior in digestibility to the resistant rice heat-treated for 4 hours, and there are some changes other than starch crystallization. It is also suggested that this is happening.

(Experiment 8)
Raw unhulled rice after harvesting (Chiba-produced husakogane, protein content 6.5% (d.b.), initial moisture content 21.2% (w.b.)) is placed in a 1 L capacity beaker and microwaved. (Hitachi Ltd., MRO-DF6) to obtain indigestible rice. Heating was performed by placing the sample in a microwave oven set to 100 W so that the mass of the sample was 1000 g, and heating was continued until the grain temperature rose to 100°C. The temperature was adjusted so that the probe tip of a fiber type thermometer (Fiberoptic Thermometer (Anritsu Meter, AMOTH FL-2000), probe (Anritsu Meter, FS100-2M)) was positioned in the center of the raw rice put in the beaker. It was measured.
After heat treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.

Table 12 shows the time required for heating, the rate of temperature increase, and the amount of resistant starch after milling.

FIG. 23 shows the evaluation results of carbohydrate digestibility of the obtained boiled rice by simulated digestion test, and Table 13 shows the equilibrium digestibility and the digestion rate constant.

It was confirmed that the digestibility of the microwave heat-treated sample was reduced compared to the control. It was confirmed that the microwave treatment can greatly shorten the treatment time compared to the wet heat treatment and the heat treatment.
Moreover, the obtained cooked rice did not differ from the control in terms of color, stickiness, appearance, etc. during the experiment.

(Experiment 9)
Raw unhulled rice after harvesting (Chiba-produced beetle, protein content 6.5% (d.b.), initial moisture content 21.2% (w.b.)) was subjected to electrolysis in the same manner as Experiment 8 above. The samples were heat-treated with a mass of 100 g, 500 g, and 1000 g depending on the range, and then immersed in hot water at 65° C. for 6 hours to obtain resistant rice.
In addition, the time required for heating with a microwave oven differs depending on the processing mass. It was 0.25°C/sec. In addition, the 100 g sample was processed in 5 groups to make a total of 500 g, in order to secure the necessary amount for subsequent rice cooking, etc., and was uniformly mixed and used for rice polishing and rice cooking.
After heat treatment, the rice was dried at 35° C. and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.

FIG. 24 shows the evaluation results of carbohydrate digestibility of the obtained boiled rice by the simulated digestion test, and Table 14 shows the rate of temperature increase, the equilibrium digestibility, and the digestion rate constant.

Compared to the control, it was confirmed that the digestibility of the sample heat-treated by microwave + hot water immersion was reduced. The extent of the decrease varies depending on the processing conditions in the microwave oven, and it was confirmed that the digestibility of the sample with a faster heating rate decreased more.
The calculated digestion rate constant also showed a lower value than the control, and it was confirmed that the faster the heating rate of the sample, the lower the rate.
Also, the cooked rice obtained from the sample that was heated in the microwave and immersed in hot water did not differ from the control in terms of color, stickiness, appearance, etc. during the experiment.

(Experiment 10)
Raw unhulled rice after harvest (Koshihikari from Chiba Prefecture, protein content 7.6% (d.b.), initial moisture content 26.9% (w.b.)) was soaked in hot water at a temperature of 65 ° C. The rice was immersed for a period of time and heat-treated to obtain resistant rice 1.
After the treatment, the rice was dried under ventilation at 35°C and 75% RH for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain indigestible cooked rice.
As a simple human test by one adult male, the blood glucose level was measured immediately after eating the indigestible cooked rice and every 30 minutes thereafter using a commercially available strip-type meter (On Call Express, ACON Laboratories, Inc.).

As control 1, raw rice after harvest (Koshihikari from Chiba Prefecture, protein content 7.6% (d.b.), initial moisture content 26.9% (w.b.)) was treated at 35 ° C., 75% The rice was dried under RH ventilation for 24 hours, hulled, polished (90% of brown rice weight), and cooked to obtain cooked rice. Control 1 is common boiled rice.
As control 2, raw rice after harvest (Koshihikari from Chiba Prefecture, protein content 7.6% (d.b.), initial moisture content 26.9% (w.b.)) was autoclaved at 121 ° C. Heat treatment is performed so as to continue for 600 seconds, and after the treatment, the rice is dried under ventilation at 35 ° C. and 75% RH for 24 hours, hulled, polished (90% based on the weight of brown rice), and cooked. rice field. Control 2 was heat treated more strongly than the invention.
Control 3 was a commercially available instant udon noodle (Toyo Suisan Co., Ltd., gotsumori kitsune udon, noodles 86 g).

In the test, only water was taken after 10:00 p.m. on the previous day, and 100 g of indigestible rice or rice was cooked with 150 ml of water at 10:00 a.m., or control 3 (commercially available instant udon) was noodles. I took only
The results are shown in FIG.

Control 1 is common boiled rice. In Control 1, the blood sugar level rose to 218 mg/dL 90 minutes after eating, which was significantly higher than the blood sugar level (70 mg/dL) immediately after eating.
In the indigestible rice of the present invention, the postprandial blood sugar level remained close to about 150 mg/dL from 60 minutes to 180 minutes, and then continued to drop, showing no sharp peak (blood sugar level spike) after meal. Moreover, its appearance and taste were almost the same as those of Control 1.
In Control 2, the increase in blood sugar level was suppressed more than in the indigestible rice of the present invention, and was 130 mg/dL after 30 minutes and about 115 mg/dL over 150 minutes thereafter. However, the resulting rice and cooked rice were brown and hard compared to the resistant rice of the present invention.
In control 3 (udon), the blood sugar level rose rapidly after eating, and after 30 minutes the blood sugar level reached 178 mg/dL. became. This is because noodles (or bread) have broken grain morphology, which facilitates the absorption of starch.

Claims

A heat treatment step of subjecting uncooked rice to heat treatment under any one or more of the following conditions (1) to (3),
A method for producing resistant rice, comprising:
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
The method for producing resistant rice according to claim 1, wherein the heat treatment step (1) or (2) is performed at 68°C or lower.
The method for producing resistant rice according to claim 1 or 2, wherein the heat treatment step (2) is performed in hot water for 12 hours or less.
The method for producing resistant rice according to claim 1, wherein the heat treatment step (3) is performed at a temperature elevation rate of 0.5°C/second or more.
An indigestible rice produced through a heat treatment step in which uncooked rice is subjected to a heat treatment under any one or more of the following conditions (1) to (3).
(1) Exposure to a high humidity atmosphere of 90% RH or higher at 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(2) It is exposed to warm water of 60° C. or higher and 80° C. or lower for 2 hours or longer and 24 hours or shorter.
(3) Heat to 60° C. or more and 100° C. or less with microwaves.
A resistant rice characterized by a digestion rate constant evaluated in a simulated digestion test that is reduced by 10% or more compared to untreated rice that has not been heat-treated.
A resistant rice characterized by a 50% or more increase in the amount of resistant starch compared to untreated rice that has not been heat-treated.