Low-GI instant rice and preparation method of low-GI instant rice through enzyme directional reconstruction

Abstract

The invention belongs to the technical field of food processing, and discloses low-GI instant rice and a preparation method of the low-GI instant rice through enzyme directional reconstitution, and the preparation method comprises the steps of raw material pretreatment, enzyme directional reconstitution modification, formula compounding, forming drying and curing sterilization. Wherein a compound enzyme system consisting of a glycogen branching enzyme mutant, an alpha-amylase inhibitor and glucosyltransferase is adopted to carry out directional modification on pretreated rice flour, the modified rice flour is compounded with low-GI coarse cereal flour components, the modified rice flour is molded into rice grains, and a finished product is prepared through a subsequent process. The problems that existing instant rice is high in GI value and contradictory in taste and instant property are solved, the starch structure is directionally regulated and controlled through enzyme, the GI is stably reduced, and the finished product is in a rice grain shape, has the low GI property, good instant property and eating taste, balanced nutrition and controllable production cost, is suitable for industrial batch production and can meet the staple food requirement of sugar-controlled people.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a low-GI fast rice and its preparation method of enzyme-directed reconstruction. Background Technology

[0002] With increasing health awareness among residents, the number of people controlling their blood sugar is constantly expanding, making instant rice, which combines convenience and low GI properties, a research hotspot in the food processing field. As a convenient staple food, the core requirements for instant rice are the synergy of speed, good taste, and nutritional health. However, current technologies struggle to achieve all three, presenting numerous unresolved issues. Currently, instant rice is mainly divided into traditional instant rice and modified low-GI instant rice. Traditional instant rice uses high-temperature cooking and hot-air drying processes, which, while meeting the need for speed, does not properly regulate the starch structure, resulting in a high GI value. Furthermore, after rehydration, it is prone to problems such as a hard center, stickiness, and a rough texture, failing to meet the needs of people controlling their blood sugar. Modified low-GI instant rice often employs physical modification, chemical modification, or single-enzyme modification processes. Physical modification struggles to achieve stable GI value control, chemical modification easily leaves harmful residues, and single-enzyme modification lacks directionality, failing to precisely regulate the starch branch chain structure, leading to large GI value fluctuations and easily damaging the original starch properties, affecting taste and speed. Furthermore, existing compound enzyme modification technologies lack targeted enzyme combinations and do not utilize specific enzyme mutants to enhance modification effects. Some technologies also produce rice noodles as finished products, limiting consumption scenarios, resulting in low consumer acceptance, and high production costs, making industrial-scale mass production difficult. Therefore, developing a method for preparing low-GI instant rice that can directionally regulate starch structure, stably reduce the GI value, and balance convenience, taste, and production costs, while being suitable for industrial production, has significant practical implications and application value. Summary of the Invention

[0003] To address the shortcomings mentioned in the background section, this invention aims to provide a low-GI instant rice and its enzyme-directed reconstruction preparation method, resolving the problems of unstable GI values ​​and the contradiction between taste and instant eating in existing technologies. The preparation method includes four steps: raw material pretreatment, enzyme-directed reconstruction modification, formula compounding, molding and drying, and cooking and sterilization. The core utilizes a composite enzyme system composed of a glycogen branching enzyme mutant, an α-amylase inhibitor, and a glucosyltransferase to directionally modify rice flour. After compounding, the rice is shaped into rice grains, and subsequent processes yield the finished product. This invention can directionally regulate starch structure, stably reduce the GI value, balance instant eating and palatability, provide balanced nutrition, controllable production costs, and is suitable for industrial production, meeting the staple food needs of people controlling their blood sugar.

[0004] The objective of this invention can be achieved through the following technical solutions: A method for preparing low-GI fast-cooking rice by enzyme-directed reconstitution includes the following steps: S1. Pre-treat the indica rice raw material; S2. A complex enzyme system consisting of a glycogen branching enzyme mutant, an α-amylase inhibitor, and a glucosyltransferase was used to perform enzyme-directed reconstructive modification on pretreated rice flour. S3. Add low-GI mixed grain powder, compound dietary fiber, prebiotics and edible salt to the enzyme-modified rice flour slurry to form a compound formula. Press the compound slurry into rice grains and then vacuum dry it. Demold the rice flour to obtain shaped instant rice grains. S4. The formed instant rice granules are steam-cooked, cooled and sterilized with ultraviolet light in sequence. After sterilization, they are packaged to obtain the low-GI instant rice product. The enzyme-directed remodeling modification is used to directionally regulate starch structure and stably reduce the GI value.

[0005] More preferably, the raw material pretreatment includes the following steps: selecting indica rice, removing impurities and washing it, draining the water and drying it at a constant temperature, crushing it and sieving it to obtain rice flour; pretreating the rice flour with microwave and cooling it to room temperature for later use.

[0006] More preferably, the constant temperature drying temperature is 40-45℃, and the rice flour is dried until the moisture content is 12-14%; the rice flour is pulverized and then passed through an 80-100 mesh sieve; the microwave pretreatment power is 300-350W, and the pretreatment time is 3-5 minutes.

[0007] More preferably, the enzyme-directed reconstructive modification in step S2 includes the following steps: adding deionized water to the pretreated rice flour, stirring evenly, adding the composite enzyme system, adjusting the pH value of the system, and placing it in a constant temperature water bath for enzymatic hydrolysis, with intermittent stirring during the enzymatic hydrolysis; after the enzymatic hydrolysis is completed, heating is used to inactivate the composite enzyme system, and after cooling, enzyme-modified rice flour slurry is obtained.

[0008] More preferably, in the compound enzyme system, the mass ratio of glycogen branching enzyme mutant, α-amylase inhibitor and glucosyltransferase is 1:(0.8-1.2):(0.5-0.7); the amount of the compound enzyme system added is 0.3-0.5% of the mass of the pretreated rice flour.

[0009] More preferably, the enzymatic hydrolysis temperature is 50-58℃, the pH value is 5.2-5.8, and the enzymatic hydrolysis time is 60-90 min; the enzyme inactivation temperature is 90-95℃, and the inactivation time is 10-15 min; the intermittent stirring method during the enzymatic hydrolysis process is stirring for 5 min every 15 min.

[0010] More preferably, the glycogen branching enzyme mutant in step S2 is a recombinant enzyme prepared by site-directed mutagenesis in genetic engineering, with an enzyme activity of not less than 1200 U / mg. The preparation method of the glycogen branching enzyme mutant includes the following steps: site-directed mutagenesis is performed using the wild-type glycogen branching enzyme gene as a template to construct a recombinant expression vector of the glycogen branching enzyme mutant; the recombinant expression vector is transformed into host cells, and positive clones are screened to obtain recombinant expression strains; the recombinant expression strains are induced to express, and the expression product is isolated and purified to obtain the glycogen branching enzyme mutant.

[0011] More preferably, the low-GI whole grain powder in step S3 is composed of oat flour and buckwheat flour mixed in a mass ratio of (1.8-2.2):1, and the amount added is 8-12% of the mass of rice flour; the compound dietary fiber is composed of konjac flour and resistant dextrin mixed in a mass ratio of (0.8-1.2):1.5, and the amount added is 5.5-7.0% of the mass of rice flour; the prebiotic is composed of fructooligosaccharides and stachyose mixed in a mass ratio of (0.8-1.2):1, and the amount added is 2.0-3.0% of the mass of rice flour; the amount of edible salt added is 0.1-0.2% of the mass of rice flour.

[0012] More preferably, in step S3, the vacuum degree of vacuum drying is 0.06-0.08 MPa, the drying temperature is 55-60℃, and the moisture content of the shaped instant rice grains is 10-12%; the pressure of steam cooking is 0.12-0.15 MPa, and the cooking time is 8-10 min; the intensity of ultraviolet sterilization is 30-40 μW / cm², and the sterilization time is 15-20 min.

[0013] A low-GI instant rice, wherein the low-GI instant rice has a rice grain-shaped structure and has low-GI properties, fast-eating properties and good taste formed after enzyme-directed reconstruction modification and formula compounding.

[0014] The beneficial effects of this invention are: This invention employs a complex enzyme system composed of a glycogen branching enzyme mutant, an α-amylase inhibitor, and a glucosyltransferase. Utilizing the higher catalytic specificity and activity of the mutant enzyme, it directionally regulates the branched structure of rice flour starch. Combined with the synergistic effect of the other two enzymes, it achieves precise reconstruction of the starch structure, stably reducing the GI value of instant rice and meeting the staple food needs of people controlling their blood sugar. This avoids the problems of large GI value fluctuations and impaired taste associated with single enzyme modification or physical / chemical modification. During the preparation process, rice is processed into rice flour and then shaped into rice granules. This ensures sufficient contact between the enzyme and starch granules, improving enzymatic hydrolysis efficiency and uniform modification, while maintaining a consumer-acceptable rice granule shape in the finished product. This avoids the limitations of rice flour in terms of consumption scenarios and the tendency to clump, balancing good convenience with a soft, chewy texture, thus resolving the contradiction between convenience and taste in existing technologies. The formulation process rationally combines low-GI whole grain powder, complex dietary fiber, and prebiotics, further enhancing the low-GI properties and improving the product's nutritional balance, meeting consumers' health needs. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 The graph shows a comparison of the dietary fiber content and prebiotic retention rate of the low-GI instant rice prepared in the examples and comparative examples. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: Verification of the preparation effectiveness of the low-GI instant rice preparation process under low process parameter combinations.

[0019] Raw material preparation: Indica rice was selected as the raw material, and impurities were removed for later use; low-GI mixed grain powder was made by mixing oat flour and buckwheat flour in a mass ratio of 1.8:1; complex dietary fiber was made by mixing konjac flour and resistant dextrin in a mass ratio of 0.8:1.5; prebiotics were made by mixing fructooligosaccharides and stachyose in a mass ratio of 0.8:1; the complex enzyme system was made by mixing glycogen branching enzyme mutant, α-amylase inhibitor and glucosyltransferase in a mass ratio of 1:0.8:0.5. Among them, the glycogen branching enzyme mutant was a recombinant enzyme prepared by site-directed mutagenesis through genetic engineering, with an enzyme activity of 1200 U / mg (the minimum enzyme activity value). It was prepared by site-directed mutagenesis using wild-type glycogen branching enzyme gene as a template, constructing a recombinant expression vector, transforming host cells, inducing expression, and isolating and purifying.

[0020] The specific preparation steps are as follows: S1. Wash the prepared indica rice, drain the water, dry it at a constant temperature of 40℃, grind it and pass it through an 80-mesh sieve to obtain rice flour, then microwave the rice flour at 300W power for 3 minutes, and cool it to room temperature for later use. S2. Add deionized water to the pretreated rice flour, stir evenly, then add the compound enzyme system at a rate of 0.3% of the rice flour mass. Adjust the pH of the system to 5.2, place it in a 50℃ constant temperature water bath for 60 min of enzymatic hydrolysis, stirring for 5 min every 15 min during the enzymatic hydrolysis. After the enzymatic hydrolysis is completed, raise the temperature to 90℃ and keep it at that temperature for 10 min to inactivate the enzyme. After cooling, the enzyme-modified rice flour slurry is obtained. S3. Add low-GI mixed grain powder (8% of the weight of rice flour), compound dietary fiber (5.5% of the weight of rice flour), prebiotics (2.0% of the weight of rice flour), and edible salt (0.1% of the weight of rice flour) to the enzyme-modified rice flour slurry, stir evenly to complete the formula compounding, press the compound slurry into rice grain shape, place it under vacuum drying at 0.06MPa and 55℃, and demold to obtain shaped instant rice grains; S4. The formed instant rice granules are sequentially steam-cooked (pressure 0.12MPa, cooking time 8min), cooled, and sterilized with ultraviolet light (intensity 30μW / cm², sterilization time 15min). After sterilization, they are packaged to obtain the low-GI instant rice.

[0021] Example 2: Verification of the preparation effectiveness of the low-GI instant rice preparation process under high process parameter combinations.

[0022] 1. Raw material preparation: Indica rice is selected as the raw material, and impurities are removed for later use; low-GI mixed grain powder is made by mixing oat flour and buckwheat flour in a mass ratio of 2.2:1; compound dietary fiber is made by mixing konjac flour and resistant dextrin in a mass ratio of 1.2:1.5; prebiotics are made by mixing fructooligosaccharides and stachyose in a mass ratio of 1.2:1; the compound enzyme system is made by mixing glycogen branching enzyme mutant, α-amylase inhibitor and glucosyltransferase in a mass ratio of 1:1.2:0.7. Among them, the glycogen branching enzyme mutant is a recombinant enzyme prepared by site-directed mutagenesis through genetic engineering, with an enzyme activity ≥1200U / mg (1500U / mg in this example). It is prepared by site-directed mutagenesis using wild-type glycogen branching enzyme gene as template, constructing recombinant expression vector, transforming host cells, inducing expression and isolation and purification.

[0023] 2. The specific preparation steps are as follows: S1. Wash the prepared indica rice, drain the water, dry it at a constant temperature of 45℃, grind it and pass it through a 100-mesh sieve to obtain rice flour. Then place the rice flour in a microwave pretreatment at 350W power for 5 minutes and cool it to room temperature for later use. S2. Add deionized water to the pretreated rice flour, stir evenly, then add the compound enzyme system at a rate of 0.5% of the rice flour mass. Adjust the pH of the system to 5.8, place it in a 58℃ constant temperature water bath for 90 min of enzymatic hydrolysis, stirring for 5 min every 15 min during the enzymatic hydrolysis. After the enzymatic hydrolysis is completed, raise the temperature to 95℃ and keep it at that temperature for 15 min to inactivate the enzyme. After cooling, the enzyme-modified rice flour slurry is obtained. S3. Add low-GI mixed grain powder (12% of the weight of rice flour), compound dietary fiber (7.0% of the weight of rice flour), prebiotics (3.0% of the weight of rice flour), and edible salt (0.2% of the weight of rice flour) to the enzyme-modified rice flour slurry, stir evenly to complete the formula compounding, press the compound slurry into rice grain shape, place it under vacuum drying at a vacuum degree of 0.08MPa and 60℃, and demold to obtain shaped instant rice grains; S4. The formed instant rice granules are sequentially steam-cooked (pressure 0.15MPa, cooking time 10min), cooled and sterilized with ultraviolet light (intensity 40μW / cm², sterilization time 20min). After sterilization, they are packaged to obtain the low-GI instant rice.

[0024] Example 3: Verification of the preparation effectiveness of the low-GI instant rice preparation process under appropriate process parameter combinations.

[0025] 1. Raw material preparation: Indica rice is selected as the raw material, and impurities are removed for later use; low-GI mixed grain powder is made by mixing oat flour and buckwheat flour at a mass ratio of 2.0:1; compound dietary fiber is made by mixing konjac flour and resistant dextrin at a mass ratio of 1.0:1.5; prebiotics are made by mixing fructooligosaccharides and stachyose at a mass ratio of 1.0:1; the compound enzyme system is made by mixing glycogen branching enzyme mutant, α-amylase inhibitor and glucosyltransferase at a mass ratio of 1:1.0:0.6. Among them, the glycogen branching enzyme mutant is a recombinant enzyme prepared by site-directed mutagenesis through genetic engineering, with an enzyme activity of 1350 U / mg. It is prepared by site-directed mutagenesis using wild-type glycogen branching enzyme gene as template, constructing recombinant expression vector, transforming host cells, inducing expression and isolation and purification.

[0026] 2. The specific preparation steps are as follows: S1. Wash the prepared indica rice, drain the water, dry it at a constant temperature of 42.5℃, grind it and pass it through a 90-mesh sieve to obtain rice flour. Then place the rice flour in a microwave pretreatment at 325W power for 4 minutes, and cool it to room temperature for later use. S2. Add deionized water to the pretreated rice flour, stir evenly, then add the compound enzyme system (addition amount is 0.4% of the mass of rice flour), adjust the pH value of the system to 5.5, place it in a 54℃ constant temperature water bath for 75 min of enzymatic hydrolysis, stirring for 5 min every 15 min during the enzymatic hydrolysis, after the enzymatic hydrolysis is completed, raise the temperature to 92.5℃, keep it at the temperature for 12.5 min to inactivate the enzyme, and after cooling, obtain the enzyme modified rice flour slurry; S3. Add low-GI mixed grain powder (10% of the weight of rice flour), compound dietary fiber (6.25% of the weight of rice flour), prebiotics (2.5% of the weight of rice flour), and edible salt (0.15% of the weight of rice flour) to the enzyme-modified rice flour slurry, stir evenly to complete the formula compounding, press the compound slurry into rice grain shape, place it under vacuum drying at a vacuum degree of 0.07MPa and 57.5℃, and demold to obtain shaped instant rice grains; S4. The formed instant rice granules are sequentially steam-cooked (pressure 0.135MPa, cooking time 9min), cooled, and sterilized with ultraviolet light (intensity 35μW / cm², sterilization time 17.5min). After sterilization, they are packaged to obtain the low-GI instant rice.

[0027] Comparative Example 1: Glycogen branching enzyme mutant in enzyme-free system, replaced with ordinary glycogen branching enzyme.

[0028] Raw material preparation: Except for replacing the compound enzyme system with "a mixture of ordinary glycogen branching enzyme, α-amylase inhibitor and glucosyltransferase in a mass ratio of 1:1.0:0.6" (the ordinary glycogen branching enzyme has an activity of 1000 U / mg and has not undergone site-directed mutagenesis), all other raw materials and ratios are completely consistent with those in Example 3.

[0029] The specific preparation steps for the low-GI fast rice are the same as in Example 3.

[0030] Comparative Example 2: Modification was performed using only a single common glycogen branching enzyme, without employing the complex enzyme system of this invention. Raw material preparation: α-amylase inhibitor and glucosyltransferase were removed from the compound enzyme system, and only ordinary glycogen branching enzyme (enzyme activity 1000U / mg) was used for modification. The amount of ordinary glycogen branching enzyme added was 0.4% of the mass of rice flour. The other raw materials and proportions were completely consistent with those in Example 3.

[0031] The specific preparation steps of the low-GI fast rice are the same as in Example 3, except that in step S2, only ordinary glycogen branching enzyme (enzyme activity 1000U / mg) of the compound enzyme system is used for modification, and the amount of ordinary glycogen branching enzyme added is 0.4% of the mass of rice flour.

[0032] Performance testing 1. Glycemic Index (GI) Test Ten healthy volunteers were selected. After fasting for 12 hours, venous blood was collected to measure fasting blood glucose levels. Each volunteer consumed 50g of the low-GI instant rice prepared in Examples 1-3 and Comparative Examples 1-2. Venous blood was collected at 30, 60, 90, and 120 minutes after consumption to measure blood glucose levels. The blood glucose values ​​at these four time points were used to calculate the area under the glycemic index (ABI) for each sample. This ABI was then compared with the ABI of the same amount of glucose to obtain the individual GI value. Three parallel measurements were performed, and the average value was taken. The results are shown in Table 1 below.

[0033] Table 1. Glycemic Index (GI value)

[0034] As shown in Table 1, the low-GI instant rice prepared in Examples 1-3 all had low GI values ​​with small fluctuation ranges. Example 3 had the lowest GI value (40) and the smallest fluctuation range (±1). Examples 1 and 2 had GI values ​​of 45 and 42 respectively, with fluctuation ranges not exceeding ±2, indicating that the preparation process of this invention can stably regulate starch structure and achieve efficient GI reduction. In contrast, Comparative Examples 1 and 2 had GI values ​​as high as 58 and 65 respectively, with fluctuation ranges of ±3 and ±4, significantly higher than the examples. This indicates that the synergistic effect of the glycogen branching enzyme mutant and the complex enzyme system of this invention can effectively solve the problems of high GI values ​​and poor stability in existing technologies, and the prepared products are more suitable for the consumption needs of people controlling their blood sugar.

[0035] 2. Rehydration performance (instant hydration) test Take 20g of each of the low-GI instant rice products prepared in Examples 1-3 and Comparative Examples 1-2, and place them in 5 identical beakers. At room temperature of 25℃, add 80mL of deionized water (rice-to-water ratio 1:4), let stand for rehydration and start timing. Observe the sample status every 1min until the sample is completely rehydrated, without a hard core and with intact particles, and record the rehydration time at this time. At the same time, observe the dispersibility of the sample during the rehydration process to determine whether clumping or adhesion occurs. Perform three parallel measurements and take the average rehydration time. The results are shown in Table 2 below.

[0036] Table 2 Results of Rehydration Performance Tests

[0037] As shown in Table 2, the low-GI instant rice prepared in Examples 1-3 all had relatively short rehydration times. Example 3 had the fastest rehydration time, requiring only 4.5 minutes, while Examples 1 and 2 had rehydration times of 5.5 minutes and 5.0 minutes, respectively. All three exhibited excellent rehydration and dispersibility, with no clumping or adhesion, indicating that the preparation process of this invention can effectively improve the product's instant eating properties. In contrast, Comparative Example 1 had a rehydration time as long as 7.5 minutes and exhibited slight clumping, while Comparative Example 2 had a rehydration time of 8.5 minutes and showed severe clumping and adhesion, significantly inferior to the examples.

[0038] 3. Nutritional composition test The dietary fiber content of each sample was determined according to GB 5009.88-2014 "Determination of Dietary Fiber in Food". The prebiotic retention rate was determined according to the routine detection logic of functional component retention rate in food. First, the prebiotic content after processing was determined according to GB 5009.255-2016 "National Food Safety Standard - Determination of Fructooligosaccharides in Food" (High Performance Liquid Chromatography), and the retention rate was calculated by combining the amount of prebiotics added before processing. 5g of each sample from Examples 1-3 and Comparative Examples 1-2 was taken, pulverized, and passed through a 40-mesh sieve for later use. Dietary fiber was determined by enzyme gravimetric method, and prebiotics were determined by high performance liquid chromatography. Each sample was measured in parallel 3 times, and the average value was taken as the final result. The results are shown in Table 3 below.

[0039] Table 3 Nutritional composition results

[0040] As shown in Table 3, the dietary fiber content and prebiotic retention rate of the low-GI instant rice prepared in Examples 1-3 were significantly higher than those in the comparative examples, showing a gradual optimization trend. Among them, Example 3 had the best performance with a dietary fiber content of 9.1g / 100g and a prebiotic retention rate of 95.8%, while Examples 1 and 2 also maintained high levels. In contrast, the dietary fiber content of Comparative Examples 1 and 2 was only 6.5g / 100g and 5.8g / 100g, respectively, and the prebiotic retention rate was less than 85%, which was significantly worse than the examples. This indicates that the synergistic effect of the compound formulation and enzyme modification of the present invention can effectively increase the dietary fiber content, reduce the loss of prebiotics, and thus improve the nutritional balance of the product.

[0041] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing low-GI fast-cooking rice with enzyme-directed reconstructive processing, characterized in that, Includes the following steps: S1. Pre-treat the indica rice raw material; S2. A complex enzyme system consisting of a glycogen branching enzyme mutant, an α-amylase inhibitor, and a glucosyltransferase was used to perform enzyme-directed reconstructive modification on pretreated rice flour. S3. Add low-GI mixed grain powder, compound dietary fiber, prebiotics and edible salt to the enzyme-modified rice flour slurry to form a compound formula. Press the compound slurry into rice grains and then vacuum dry it. Demold the rice flour to obtain shaped instant rice grains. S4. The formed instant rice granules are steam-cooked, cooled and sterilized with ultraviolet light in sequence. After sterilization, they are packaged to obtain the low-GI instant rice product. The enzyme-directed remodeling modification is used to directionally regulate starch structure and stably reduce the GI value.

2. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 1, characterized in that, The raw material pretreatment includes the following steps: selecting indica rice, removing impurities and washing, draining the water and drying at a constant temperature, crushing and sieving to obtain rice flour; pretreating the rice flour with microwave and cooling it to room temperature for later use.

3. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 2, characterized in that, The constant temperature drying temperature is 40-45℃, and the rice flour is dried until the moisture content is 12-14%; the rice flour is pulverized and then passed through an 80-100 mesh sieve; the microwave pretreatment power is 300-350W, and the pretreatment time is 3-5 minutes.

4. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 1, characterized in that, In step S2, enzyme-directed remodeling modification The process includes the following steps: adding deionized water to pretreated rice flour, stirring evenly, adding the compound enzyme system, adjusting the pH value of the system, and placing it in a constant temperature water bath for enzymatic hydrolysis, with intermittent stirring during the enzymatic hydrolysis process; after the enzymatic hydrolysis is completed, heating is used to inactivate the compound enzyme system, and after cooling, enzyme-modified rice flour slurry is obtained.

5. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 4, characterized in that, In the complex enzyme system, the mass ratio of glycogen branching enzyme mutant, α-amylase inhibitor and glucosyltransferase is 1:(0.8-1.2):(0.5-0.7); the amount of the complex enzyme system added is 0.3-0.5% of the mass of the pretreated rice flour.

6. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 4, characterized in that, The enzymatic hydrolysis temperature is 50-58℃, the pH value is 5.2-5.8, and the hydrolysis time is 60-90 min; the enzyme inactivation temperature is 90-95℃, and the inactivation time is 10-15 min; the intermittent stirring method during the enzymatic hydrolysis process is to stir for 5 min every 15 min.

7. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 1, characterized in that, The glycogen branching enzyme mutant mentioned in step S2 is a recombinant enzyme prepared by site-directed mutagenesis in genetic engineering, with an enzyme activity of not less than 1200 U / mg. The preparation method of the glycogen branching enzyme mutant includes the following steps: site-directed mutagenesis is performed using the wild-type glycogen branching enzyme gene as a template to construct a recombinant expression vector of the glycogen branching enzyme mutant; the recombinant expression vector is transformed into host cells, and positive clones are screened to obtain recombinant expression strains; the recombinant expression strains are induced to express, and the expression product is isolated and purified to obtain the glycogen branching enzyme mutant.

8. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 1, characterized in that, The low-GI whole grain powder mentioned in step S3 is composed of oat flour and buckwheat flour mixed in a mass ratio of (1.8-2.2):1, and the amount added is 8-12% of the mass of rice flour; the compound dietary fiber is composed of konjac flour and resistant dextrin mixed in a mass ratio of (0.8-1.2):1.5, and the amount added is 5.5-7.0% of the mass of rice flour; the prebiotic is composed of fructooligosaccharides and stachyose mixed in a mass ratio of (0.8-1.2):1, and the amount added is 2.0-3.0% of the mass of rice flour; the amount of edible salt added is 0.1-0.2% of the mass of rice flour.

9. The method for preparing low-GI fast-cooking rice with enzyme-directed reconstruction according to claim 1, characterized in that, In step S3, the vacuum drying process involves a vacuum degree of 0.06-0.08 MPa, a drying temperature of 55-60°C, and drying until the moisture content of the formed instant rice grains is 10-12%. The steam cooking process involves a pressure of 0.12-0.15 MPa and a cooking time of 8-10 min. The ultraviolet sterilization process involves an intensity of 30-40 μW / cm² and a sterilization time of 15-20 min.

10. A low-GI instant rice, characterized in that, The low-GI instant rice, prepared by the enzyme-directed reconstructing method according to any one of claims 1-9, has a rice grain-shaped structure and possesses low-GI properties, fast-eating properties, and palatability formed after enzyme-directed reconstructing modification and formulation compounding.

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