Low glycemic index rice and preparation method thereof

Abstract

The present invention provides a low-glycemic index rice and a preparation method thereof, characterized in that the rice is tempered by adding water, first subjected to microwave treatment, then rapidly frozen, and then heated to a temperature-recovering state to obtain the low-glycemic index rice. The method of the present invention can produce a GI value of less than 55 and a starch gastrointestinal digestion rate constant of less than 0.055 min. ‑1 The product is a low-glycemic index rice, and it can better keep the original nutrients of the rice from being lost, while also maintaining the original shape and appearance quality of the rice.

Description

Technical Field

[0001] The invention relates to a rice processing method, in particular to low-glycemic index rice and a preparation method thereof. Background Art

[0002] The glycemic index (GI) evaluates the effect of carbohydrates in a food on blood glucose levels and is a measure of the glycemic response a food triggers. Generally, foods with a GI value below 55 are considered low-GI, those between 55 and 70 are considered medium-GI, and those above 70 are considered high-GI. Consuming easily digestible starches or foods with a high glycemic index (GI) can cause a sharp rise in blood glucose, stimulate insulin secretion and release, and accelerate the conversion of blood glucose into fat, leading to hyperlipidemia and obesity. Obesity is a high-risk factor for conditions such as hypertension and diabetes. Drastic blood glucose fluctuations can also activate oxidative stress pathways, promote local inflammation, and lead to vascular epithelial cell damage and pathology, potentially contributing to coronary heart disease, stroke, retinopathy, and kidney disease. Consuming foods with a low GI can prolong the digestion, absorption, or metabolization of starch and sugars, allowing for a slow and sustained release of energy, reducing the burden on the pancreas, and helping to maintain postprandial blood glucose balance, thereby controlling weight and preventing various chronic diseases. Given their importance in regulating dietary health, the research and development of low-GI foods has become a hot topic in the development of healthy and nutritious foods.

[0003] A Chinese invention patent (application number 201610922229.X) discloses a low-glycemic index (GI) grain rice and its production method. The GI of the low-GI grain rice is below 50, and the grain is selected from rice, Job's tears, corn, millet, red rice, black rice, or a combination thereof. Production of the low-GI grain rice involves soaking the grains in water, draining the water, adding a cooking liquid for cooking, filtering the cooking liquid, aging, and drying. While the invention claims that the low-GI grain rice contains effective whole-grain nutrients and does not significantly increase the glycemic index after consumption, the patented method requires soaking and cooking the raw materials, which can affect their texture, original form, and nutritional properties. For example, soaking, cooking, and filtering the cooking liquid can lead to nutrient loss, and cooking can affect the texture of the raw materials.

[0004] For example, a Chinese invention patent (application number 201710716274.4) discloses a method for preparing rice that significantly increases resistant starch without adding chemicals. The method includes the following steps: (1) soaking rice in water that exceeds the amount of rice; (2) transferring the soaked rice and the soaking water to an ultrasonic device for ultrasonic pretreatment; (3) separating the rice from the soaking water, draining the soaking water, adding water again, and placing it in an autoclave for high-temperature and high-pressure treatment to produce gelatinized rice; (4) cooling the gelatinized rice naturally to room temperature; (5) transferring the cooled rice to a refrigerator for refrigeration to promote starch crystallization and aging; (6) producing rice with increased resistant starch. The rice with increased resistant starch produced by this invention has low reaction requirements, simple operation, strong applicability, and significant effect. It is a method for preparing rice that significantly increases resistant starch without adding chemicals. However, the above patented technical solution still requires soaking the rice and adding water to gelatinize the rice, which will also cause the loss of nutrients in the rice and damage the original shape and texture characteristics.

[0005] For example, a Chinese invention patent (application number 201810794389.X) discloses a method for preparing low-glycemic reconstituted rice. This method involves first preparing a low-glycemic resistant starch by low-temperature complexation of starch with lipids in an alcohol-water system, followed by temperature-dependent crystallization. This low-glycemic resistant starch is then used as the primary raw material to produce low-glycemic reconstituted rice via extrusion. The low-glycemic resistant starch produced using this method has the functions of controlling postprandial blood sugar, protecting and transporting fatty acids, and delaying starch aging. Furthermore, the low-glycemic reconstituted rice produced using this method is suitable for consumption by people with type 2 diabetes, offering advantages such as increasing the added value of agricultural and sideline products, reducing the production cost of instant rice, and improving the efficiency of instant rice production. However, the aforementioned patented solution requires the addition of chemical reagents such as ethanol and the use of extrusion technology to produce the reconstituted rice, resulting in significant differences in food safety and taste compared to ordinary rice.

[0006] In summary, although the prior art discloses methods for preparing low GI rice or grains, the products prepared by these methods usually have the following problems: (1) the raw materials need to be soaked, cooked with water, and the cooking liquid needs to be filtered out after cooking, which will cause the loss of nutrients in the product; (2) after the raw materials are soaked, cooked, dried, or reorganized, the morphology and texture characteristics of the prepared products are quite different from those of natural rice, which is not easy for consumers to accept; (3) some chemical reagents may need to be added, which greatly reduces the food safety of the product. Summary of the Invention

[0007] In view of the above problems, the present invention provides a method for preparing low glycemic index rice. The method can produce rice with a GI value lower than 55 and a starch gastrointestinal digestion rate constant lower than 0.055 min. -1 The product is a low-glycemic index rice, and it can better keep the original nutrients of the rice from being lost, while also maintaining the original shape and appearance quality of the rice.

[0008] The present invention is achieved through the following technical solutions.

[0009] In one aspect, the present invention provides a method for preparing low-glycemic index rice, which is characterized in that the rice is tempered by adding water and then subjected to microwave treatment, followed by rapid freezing and subsequent heating and temperature recovery treatment to obtain the low-glycemic index rice.

[0010] As a specific technical solution, the method for preparing the low glycemic index rice comprises the following steps:

[0011] S1, adding water and conditioning: spraying hot steam to the surface of rice to increase the moisture content of the rice surface by 1% to 2% and make the gelatinization degree of the rice surface reach more than 80%, and set aside;

[0012] S2, pulse microwave treatment: treating the rice after the conditioning treatment in step S1 with microwaves until the rice resistant starch content is greater than 15%;

[0013] S3, rapid freezing: quickly reducing the average temperature of the rice after the treatment in step S2 to -40°C or below, so that the rice is in a frozen state and maintained for more than 1 hour;

[0014] S4, heating back to temperature: heating the rice frozen in step S3 back to temperature to obtain low glycemic index rice.

[0015] As a specific technical solution, in step S1, the temperature of the hot steam is greater than 100° C., and the injection time of the hot steam is less than 5 s.

[0016] As a specific technical solution, in step S2, the microwave treatment uses low-density pulsed microwaves.

[0017] As a specific technical solution, the parameters of the low-density pulse microwave are: frequency 910 MHz~2500 MHz, energy density less than 0.005 J / g, processing time 10min~20min, and pulse period 0.1 s~1 s.

[0018] As a specific technical solution, in step S3, the rice is placed in cold air at -80°C to -30°C for 1 min to 10 min, so that the average temperature of the rice grains drops to -40°C or below, and the rice is frozen and maintained for more than 1 hour.

[0019] As a specific technical solution, the step S4 specifically includes heating the rice frozen in step S3 to 5°C~10°C using air at -40°C~10°C gradually, and controlling the average rising rate of the rice surface temperature to not exceed 5°C / min.

[0020] As a specific technical solution, the parameters of the gradual temperature change heating are as follows: the frozen rice is placed in air at -40°C for 2 minutes, in air at -30°C for 3 minutes, in air at 5°C for 5 minutes, and in air at 10°C for 2 minutes.

[0021] On the other hand, the present invention also provides a low glycemic index rice, which is prepared by any of the above methods.

[0022] As a specific technical solution, the GI value of the rice is lower than 55, and the gastrointestinal digestion rate constant of the starch of the rice is lower than 0.055 min -1 , and has the appearance quality of natural rice.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1) Compared with traditional methods for preparing low-GI rice or grains, the method of the present invention is simpler and does not cause the loss of rice nutrients. At the same time, it can maintain the original shape and appearance quality of the rice. The prepared product has higher nutritional quality and is more easily accepted by consumers. In addition, the method of the present invention does not require the addition of other chemical reagents, and the low-glycemic index rice prepared is safer to eat.

[0025] 2) The present invention conditions the rice grains by adding water to fully absorb water, then subjecting the rice to pulse microwave treatment to uniform temperature distribution and rapid ripening. Simultaneously, the conformation of rice starch molecules is regulated to form a relatively ordered double helical structure. Rapid freezing stabilizes the starch molecular structure, slowing down molecular structural changes during storage. After heating back to temperature, the product can have the appearance of natural rice.

[0026] 2) The low glycemic index rice prepared by the method of the present invention has a GI value lower than 55 and a gastrointestinal digestion rate constant of starch lower than 0.055 min -1 Long-term consumption of the low-glycemic index rice prepared by the present invention will be beneficial to people's blood sugar regulation and prevention of various chronic diseases. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be pointed out that the following embodiments are merely illustrative of the present invention in the form of examples, but the scope of protection of the present invention is not limited thereto. All equivalent replacements made by those skilled in the art to the present invention in the spirit of the present invention fall within the scope of protection of the present invention.

[0028] Example 1

[0029] A method for preparing low glycemic index rice specifically comprises the following steps:

[0030] S1. Adding water and conditioning: In this embodiment, the raw rice is commercially available jasmine rice with a moisture content of 13.3%. The rice is sprayed with superheated steam at a temperature greater than 100° C. for 5 seconds to increase the surface moisture content of the rice by 1% to 2%, so that the surface gelatinization degree of the rice reaches more than 80%, thereby obtaining surface pre-gelatinized rice for standby use. After testing, the moisture content of the rice after the water conditioning treatment reaches 14.1%, and the surface gelatinization degree of the rice is 86%.

[0031] S2. Microwave treatment: The surface pregelatinized rice was treated with microwaves at a frequency of 2450 MHz and an energy density of 0.003 J / g for 16 minutes with a pulse period of 0.5 seconds. The microwave-treated rice had a resistant starch content of 18%.

[0032] S3. Rapid freezing: placing the microwave-treated rice in cold air at -60°C for 6 minutes to reduce the average temperature of the rice grains to -50°C, and maintaining this temperature for 2.5 hours; testing shows that the resistant starch content of the frozen rice remains between 22% and 23% when stored at a temperature of 15-20°C for 1-30 days;

[0033] S4. Heating and returning to temperature: The rice frozen in step S3 was gradually heated to 5°C-10°C using air at a temperature of -40°C-10°C, and the rate of increase of the rice surface temperature was controlled to be no more than 5°C / min, thereby obtaining low-glycemic index rice. The protein, fat, and starch contents of the rice prepared in this embodiment and the control (jasmine rice) were measured and compared, and the results are shown in Table 1. Simultaneously, the rice prepared in this embodiment and the control (jasmine rice) were cooked in a Midea MB-FB40Q1-401J rice cooker to obtain rice. The GI value, starch gastrointestinal digestion rate constant, and sensory quality of the cooked rice were measured and compared, and the results are shown in Table 2.

[0034] Table 1 Comparison of nutrient content before and after processing

[0035]

[0036] As can be seen from Table 1, after the raw rice is processed by the method of the present invention, the protein, fat and starch contained in it remain substantially unchanged, so the present invention will not cause the loss of rice nutrition.

[0037] Table 2 Quality test of low glycemic index rice after cooking

[0038]

[0039] As shown in Table 2, the GI value of the low glycemic index rice prepared by the present invention after cooking is 53, and the gastrointestinal digestion rate constant of starch is 0.051min -1 The sensory quality of the low-glycemic index rice is the shape and color of natural rice. The GI value of the low-glycemic index rice obtained by the process steps of the present invention is significantly lower than that of the untreated control sample rice, and the mouthfeel is moderately soft and hard, and the elasticity is slightly better than the control. The appearance is basically the same as the raw rice. Example 2

[0040] Optimization of microwave treatment in the present invention: The method for producing low glycemic index rice in Example 1 was used, wherein the technical parameter settings for microwave treatment in step S2 were slightly different. The technical parameter settings and the GI value and digestion rate constant test results are shown in Table 3.

[0041] Table 3 Effects of microwave parameters on rice quality

[0042]

[0043] Note: No. 1 is the control, i.e., no microwave treatment;

[0044] Table 3 shows that Sample 2 has a low GI and excellent taste. Sample 3, with a slightly lower microwave intensity (less microwave treatment time than Sample 2), has an excellent taste (similar to Sample 1), but a higher GI. Sample 4, with a slightly higher microwave intensity (higher microwave power density than Samples 2 and 3), has the lowest GI but a harder texture. Sample 5, compared to Sample 4, has an improved taste but a higher GI. Samples 6 and 7, with overly strong microwave treatment conditions, have experienced some puffing. In summary, Sample 2 exhibits the optimal microwave treatment parameters: an energy density of 0.003 J / g, a treatment time of 16 minutes, and a pulse period of 0.5 seconds. Example 3

[0045] Optimization of the rapid freezing parameters in the present invention. The method for preparing low-glycemic index rice in Example 1 was used, wherein the parameter settings for the rapid freezing in step S3 were slightly different. The average final temperature and resistant starch content of the prepared low-glycemic index rice were finally measured. The parameter settings, average final temperature, and resistant starch content test results are specifically shown in Table 4.

[0046] Table 4 Effects of freezing parameters on rice quality

[0047]

[0048] Note: No. 1 is the control, which is not frozen.

[0049] Table 4 shows that for samples 3 to 5, at the same freezing time, the average final temperature of the rice gradually decreased as the air temperature decreased. When the average final temperature dropped below -40°C (i.e., for samples 4 and 5, at air temperatures of -60°C and -80°C, respectively), the resistant starch content of sample 4 remained between 22% and 23%, and that of sample 5 remained around 25%, indicating relatively stable resistant starch content. For samples 4, 6, and 7, at the same air temperature, the average final temperature of the rice gradually decreased with prolonged freezing time. Within the measured average final temperature range (-58°C to -40°C), the resistant starch content remained relatively stable. Based on the above analysis, whether controlling the air temperature or the freezing time, the average final temperature of the low glycemic index rice should be ≤-40°C. This is beneficial for maintaining the stability of the resistant starch content of the low glycemic index rice during storage. Therefore, in the present invention, the average temperature of the rice after rapid freezing should be controlled to be less than or equal to -40°C. Example 4

[0050] Optimization of heating and reheating parameters in the present invention. The method for preparing low-glycemic index rice in Example 1 was used, wherein the technical parameters for heating and reheating in step S4 were set slightly differently. The surface crack rate and GI value of the prepared low-glycemic index rice were finally measured. The specific parameter settings and results are shown in Table 5.

[0051] Table 5 Effects of heating parameters on rice quality

[0052]

[0053] Note: No. 1 is the control, i.e. no heating treatment; heating parameters a) “℃ / min -℃ / min -℃ / min” indicates the first heating temperature and time, the second heating temperature and time, the third heating temperature and time, and finally storage at ambient temperature.

[0054] Table 5 shows that when the frozen rice was heated in a stepwise heating process (exposing it to -40°C air for 2 minutes, -30°C air for 3 minutes, 5°C air for 5 minutes, and 10°C air for 2 minutes), the crack rate of sample 2 was 1.9%. Due to the slow heating temperature change and the average rate of increase in rice surface temperature of only 5°C / min, this rate is close to that of the rice without heat treatment (1.8%). However, the more severe the temperature change in samples 3 to 5, the higher the crack rate, the lower the commercial value.

Claims

1. A method for preparing low glycemic index rice, characterized in that: The following steps are involved: S1, adding water and conditioning: spraying hot steam to the surface of rice to increase the moisture content of the rice surface by 1% to 2% and make the gelatinization degree of the rice surface reach more than 80%, and set aside; S2, microwave treatment: the rice after the conditioning treatment in step S1 is treated with low-density pulse microwave until the rice resistant starch content is greater than 15%; the parameters of the low-density pulse microwave are: frequency 910 MHz to 2500 MHz, energy density less than 0.005 J / g, treatment time 10 min to 20 min, and pulse period 0.1 s to 1 s; S3, quick freezing: placing the rice after step S2 treatment in cold air at -80°C to -60°C for 6 min to 20 min, so that the average temperature of the rice grains drops to -40°C or below, and the rice is in a frozen state, and maintained for more than 1 hour; S4, heating back to temperature: the rice after being frozen in step S3 is gradually heated to 5°C~10°C with air at a temperature of -40°C~10°C, and the average rate of rise of the rice surface temperature is controlled to be no more than 5°C / min, thereby obtaining low glycemic index rice.

2. The method for preparing low glycemic index rice according to claim 1, wherein In step S1, the temperature of the hot steam is greater than 100° C., and the injection time of the hot steam is less than or equal to 5 s.

3. The method for preparing low glycemic index rice according to claim 1, wherein: The parameters of the gradual temperature change heating are as follows: the frozen rice is placed in air at -40°C for 2 minutes, in air at -30°C for 3 minutes, in air at 5°C for 5 minutes, and in air at 10°C for 2 minutes.

4. A low glycemic index rice, characterized in that: Prepared by the method according to any one of claims 1 to 3.

5. The low glycemic index rice according to claim 4, wherein: The GI value of the rice is lower than 55, and the gastrointestinal digestion rate constant of the starch of the rice is lower than 0.055 min -1 , and has the appearance quality of natural rice.

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