Preparation method of recombinant rice based on millet

Abstract

The invention belongs to the technical field of recombinant rice, and particularly relates to a millet-based recombinant rice preparation method, which comprises: S1, preparing rice and millet, the millet accounting for 40-80% of the total mass of the rice and the millet; s2, crushing the prepared rice and millet, sieving, and mixing to obtain mixed rice flour; s3, putting the mixed rice flour into a twin-screw extruder, extruding and curing the mixed rice flour by using the twin-screw extruder, and cutting and granulating to obtain recombined rice grains; and S4, drying the recombinant rice grains, and cooling to obtain a recombinant rice finished product. By limiting the addition proportion of the millet and matching with specific twin-screw extrusion parameters, the nutrition density, texture characteristics and processing stability of the recombinant rice are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of recombinant rice, and particularly relates to a method for preparing recombinant rice based on millet. Background Art

[0002] Recombined rice is a rice product made by recombining and processing different types of grains or other raw materials through modern processing technology. Usually rice flour is used as the main raw material, and other grain flours such as corn flour and oat flour are added. Some functional ingredients such as dietary fiber, vitamins, minerals, etc. may also be added to improve the nutritional content and functional characteristics of rice, making up for the relatively single nutritional content of traditional rice.

[0003] Currently, recombinant rice is rarely made by combining millet with rice. The reason is that there are differences in the physical and chemical properties of millet and rice, which leads to problems such as too high or too low viscosity, poor formability, and rough taste during the extrusion and ripening process after the two are mixed.

[0004] However, my country is one of the origins of millet, with abundant millet resources. Millet itself is a nutritious grain rich in dietary fiber, vitamins and minerals. Adding millet can significantly improve the nutritional value of recombinant rice, and has a positive effect on intestinal health and prevention of chronic diseases.

[0005] Therefore, how to solve the compatibility problem of millet and rice mixed system and achieve the coordinated optimization of recombinant rice in nutrition, taste and processing adaptability has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for preparing recombinant rice based on millet, which effectively improves the nutritional density, texture characteristics and processing stability of the recombinant rice by limiting the millet addition ratio to 60% of the core ratio and combining specific twin-screw extrusion parameters.

[0007] The specific technical solution adopted by the present invention is:

[0008] A method for preparing recombinant rice based on millet, comprising the following steps:

[0009] S1. preparing rice and millet, wherein the millet accounts for 20%-80% of the total mass of the rice and millet;

[0010] S2, crushing the prepared rice and millet, then sieving and mixing to obtain mixed rice flour;

[0011] S3, putting the mixed rice flour into a twin-screw extruder, using the twin-screw extruder to extrude and ripen the mixed rice flour, and cutting and granulating the mixed rice flour to obtain reconstituted rice grains;

[0012] S4. After drying and cooling the recombinant rice grains, the finished recombinant rice product is obtained.

[0013] Furthermore, the millet accounts for 55%-65% of the total mass of the rice and millet.

[0014] Furthermore, the millet accounts for 60% of the total mass of the rice and millet.

[0015] Furthermore, the sieving in step S2 is sieving through a 70-90 mesh sieve.

[0016] Furthermore, the parameter settings of the twin-screw extruder in step S3 are as follows: the feeding rate is 120-180 g / min, the water addition amount of the material is 34%-38%, the screw rotation speed is 120-180 r / min, the extrusion temperature in zone II is 75-85 °C, the extrusion temperature in zone III is 82-88 °C, the extrusion temperature in zone IV is 82-88 °C, the extrusion temperature in zone V is 88-92 °C, the extrusion temperature in zone VI is 88-92 °C, and the cutter rotation speed is 1400-1600 r / min.

[0017] Furthermore, the parameter settings of the twin-screw extruder in step S3 are as follows: the feeding rate is 150 g / min, the water addition amount of the material is 36%, the screw rotation speed is 150 r / min, the extrusion temperature in zone II is 80 °C, the extrusion temperature in zone III is 85 °C, the extrusion temperature in zone IV is 85 °C, the extrusion temperature in zone V is 90 °C, the extrusion temperature in zone VI is 90 °C, and the cutter rotation speed is 1500 r / min.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. In the present invention, the core ratio of the millet addition amount of 60% is defined. The recombinant rice made from this ratio has rich nutritional components. The contents of crude protein, crude fat, dietary fiber and minerals (ash) in the recombinant rice are significantly higher than those of the single-rice recombinant rice and the low-ratio millet recombinant rice. Moreover, the overall color is good, presenting a uniform rice yellow, which improves the visual attractiveness of the recombinant rice.

[0020] In addition, the content of rapidly digestible starch (RDS) in the recombinant rice under this ratio is as high as 71.26%, which can quickly release energy. At the same time, the ratio of slowly digestible starch (SDS) to resistant starch (RS) is moderate, taking into account intestinal health while providing instant energy. Its starch structure forms moderate cross-linking during the extrusion cooking process, avoiding both the too slow digestion rate caused by excessive millet and the rapid blood sugar increase problem of single rice, and achieving precise regulation of digestion characteristics.

[0021] 2. By defining the core ratio of millet at 60% and combining specific twin-screw extrusion parameters, the present invention enables a synergistic effect between the two. Millet starch granules are relatively small and the protein content is relatively high. At a ratio of 60% and under the condition of 36% moisture, it can not only ensure that the mixed powder forms a uniform dough-like material in the extruder, avoiding excessive dryness of the material and excessive extrusion resistance caused by too much millet, but also promote the interaction between millet protein and rice starch through moisture, forming a stable three-dimensional network structure, thereby enhancing the formability and cooking stability of the reconstituted rice grains.

[0022] The setting of the temperature gradient (80 °C in Zone II, 85 °C in Zone III / IV, 90 °C in Zone V / VI) and the screw speed (150 r / min) minimizes the loss rate of heat-sensitive nutrients in millet, while ensuring sufficient gelatinization of rice and millet starches in Zone V / VI (90 °C); the screw speed of 150 r / min provides an appropriate shear force, which not only breaks starch granules to promote gelatinization but also avoids excessive shear damage to the functionality of millet protein, enabling the reconstituted rice to have good elasticity and fluffiness after cooking.

[0023] The cutter speed (1500 r / min) matches the viscosity of the mixed rice flour with a 60% millet ratio, ensuring uniform particle size after cutting and avoiding adhesion or irregular particles caused by excessive viscosity of the material due to too high a millet content. Brief Description of the Drawings

[0024] Figure 1 Shows the influence of different millet addition amounts on the composition of the reconstituted rice;

[0025] Figure 2 Presents the appearance photos of the reconstituted rice with different millet addition amounts;

[0026] Figure 3 Displays the SEM morphology scanning diagrams of different reconstituted rice;

[0027] Figure 4 Illustrates the influence of different millet addition amounts on the XRD of the reconstituted rice;

[0028] Figure 5 Presents the sensory evaluation radar charts of the reconstituted rice with different millet addition ratios;

[0029] Figure 6 Shows the total sensory evaluation scores of the reconstituted rice with different millet addition ratios;

[0030] Figure 7 Illustrates the influence of different millet addition amounts on the digestion characteristics of the reconstituted rice;

[0031] Figure 8 Shows the influence of different millet addition amounts on the fatty acid content of the reconstituted rice;

[0032] Figure 9Effect of different millet addition amounts on the moisture distribution of recombinant rice;

[0033] Figure 10 Effect of different millet addition amounts on the amino acid content of recombinant rice. Specific embodiments

[0034] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments: I. Specific embodiments

[0036] Example 1

[0037] S1. Prepare rice and millet, where the millet accounts for 20% of the total mass of rice and millet;

[0038] S2. Crush the prepared rice and millet, then pass through an 80-mesh sieve, and mix to obtain a mixed rice flour;

[0039] S3. Feed the mixed rice flour into a twin-screw extruder, and use the twin-screw extruder to extrude and cook, and cut into pellets the mixed rice flour to obtain recombinant rice grains;

[0040] The parameter settings of the twin-screw extruder are: feeding rate 150 g / min, water addition amount of the material 36%, screw rotation speed 150 r / min, extrusion temperature in zone II 80 °C, extrusion temperature in zone III 85 °C, extrusion temperature in zone IV 85 °C, extrusion temperature in zone V 90 °C, extrusion temperature in zone VI 90 °C, cutter rotation speed 1500 r / min.

[0041] S4. Conduct pneumatic drying on the recombinant rice grains, and obtain the finished recombinant rice after cooling to room temperature.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is only that in S1 of Example 2, the millet accounts for 40% of the total mass of rice and millet; the remaining steps are the same as those in Example 1.

[0044] Example 3

[0045] The difference between Example 3 and Example 1 is only that in S1 of Example 3, the millet accounts for 60% of the total mass of rice and millet; the remaining steps are the same as those in Example 1.

[0046] Example 4

[0047] The difference between Example 4 and Example 1 is only that in S1 of Example 4, the millet accounts for 80% of the total mass of rice and millet; the remaining steps are the same as those in Example 1.

[0048] Comparative Example 1

[0049] In Comparative Example 1, no millet is added, and the specific steps are as follows:

[0050] S1. Crush the prepared rice, then sieve it through a 80-mesh sieve to obtain rice flour;

[0051] S2. Put the rice flour into a twin-screw extruder, and use the twin-screw extruder to extrude and cook, and cut and granulate the rice flour to obtain recombinant rice grains;

[0052] The parameters of the twin-screw extruder are set as follows: feeding rate 150 g / min, water addition amount of the material 36%, screw rotation speed 150 r / min, extrusion temperature in zone II 80 °C, extrusion temperature in zone III 85 °C, extrusion temperature in zone IV 85 °C, extrusion temperature in zone V 90 °C, extrusion temperature in zone VI 90 °C, cutter rotation speed 1500 r / min.

[0053] S4. Conduct pneumatic drying on the recombinant rice grains, and obtain the finished product of recombinant rice after cooling to room temperature.

[0054] Comparative Example 2

[0055] In Comparative Example 2, no rice is added, and the specific steps are as follows:

[0056] S1. Crush the prepared millet, then sieve it through a 80-mesh sieve to obtain millet flour;

[0057] S2. Put the millet flour into a twin-screw extruder, and use the twin-screw extruder to extrude and cook, and cut and granulate the millet flour to obtain recombinant rice grains;

[0058] The parameters of the twin-screw extruder are set as follows: feeding rate 150 g / min, water addition amount of the material 36%, screw rotation speed 150 r / min, extrusion temperature in zone II 80 °C, extrusion temperature in zone III 85 °C, extrusion temperature in zone IV 85 °C, extrusion temperature in zone V 90 °C, extrusion temperature in zone VI 90 °C, cutter rotation speed 1500 r / min.

[0059] S4. Conduct pneumatic drying on the recombinant rice grains, and obtain the finished product of recombinant rice after cooling to room temperature.

[0060] II. Performance Test

[0061] Record the finished products of recombinant rice in Examples 1-4 as CZ-20%, CZ-40%, CZ-60% and CZ-80% respectively, record the finished products of recombinant rice in Comparative Example 1 and Comparative Example 2 as rice and millet respectively, and then conduct detection respectively.

[0062] 1. Detection of basic composition

[0063] (1) Moisture content: Determine according to the national food safety standard Determination of Moisture in Foods GB 5009.3-2016.

[0064] (2) Ash content: Determined according to GB 5009.4-2016 National Food Safety Standard - Determination of Ash in Foods.

[0065] (3) Protein content: Determined according to GB 5009.5-2016 National Food Safety Standard - Determination of Protein in Foods.

[0066] (4) Fat content: Determined according to GB 5009.6-2016 National Food Safety Standard - Determination of Protein in Foods.

[0067] (5) Dietary fiber: Determined by GB / T 37492-2019 Cereals and Oils Inspection - Determination of Water-soluble Dietary Fiber in Cereals and Their Products - Enzymatic Gravimetric Method; and GB 5009.88-2014 National Food Safety Standard - Determination of Dietary Fiber in Foods.

[0068] (6) Starch content: Determined according to GB 5009.9-2023 National Food Safety Standard - Determination of Starch in Foods.

[0069] The detection of basic components determined the contents of moisture, ash, crude fat, crude protein, starch, and dietary fiber in the recombinant rice with different percentages of millet addition (as Figure 1 shown). The main component in each recombinant rice was still starch, with its content ranging from 64.61% to 70.08%. The recombinant rice with 80% millet addition had the highest starch content, reaching 70.08 ± 1.44%. Compared with rice (64.61 ± 0.92%), the starch content of the recombinant rice increased to varying degrees. This was because the starch content of millet (68.29 ± 1.85%) was higher than that of rice, and after recombination, the starch content increased compared to rice. Although the recombinant rice with 60% addition had the lowest starch content, which was 64.62 ± 0.61%, it still showed a certain degree of increase.

[0070] As the millet addition increased, the ash, crude fat, and crude protein contents of the recombinant rice also increased accordingly, while the moisture content did not show significant changes. This indicated that the increase in starch content was mainly attributed to the high starch ratio of millet, and the increased millet addition directly promoted the increase in the starch content of the recombinant rice. The increase in ash, crude fat, and crude protein was also related to the higher contents of these components in millet.

[0071] When the proportion of millet is 60%, the starch content of the recombined rice is the lowest. This is because millet starch granules are smaller and the proportion of amylopectin is higher, and its gelatinization temperature is lower than that of rice starch. In the high-temperature environment from Zone III to Zone VI of the extruder, when the proportion of millet is 60%, a large amount of millet starch will quickly gelatinize and degrade due to high-temperature shear force, generating low-molecular products such as dextrin and maltose. Therefore, the starch content of the recombined rice is low. Compared with the case when the proportion of millet is 20%, at this time rice starch dominates, and the overall starch system has stronger tolerance to high-temperature shear and lower degradation degree. Therefore, the starch retention rate is higher.

[0072] When the proportion of millet increases to 80%, the starch content rises to 70%. This is because the proportion advantage of millet exceeds part of the degradation loss, and the "high base number" in total compensates for the degradation.

[0073] Further analysis shows that the moisture content does not show significant changes, indicating that the addition of millet has limited impact on the moisture content. Generally speaking, the nutritional characteristics of millet make it an ideal ingredient for recombined rice. Millet is not only rich in starch, but also contains relatively high dietary fiber and protein, which can improve the nutritional density of food. In addition, the increase in dietary fiber may help increase satiety, thus having a positive impact on weight loss or weight maintenance. To sum up, the addition of millet not only improves the nutritional components of the recombined rice, but also has a potential impact on its texture and taste.

[0074] 2. Chromaticity determination

[0075] The chromaticity is determined by a DC-P3 full-automatic color difference meter. The instrument is first calibrated with a white calibration plate, and the L, a, b values of the sample are recorded. The measurement results are shown in Table 1 and Figure 2 .

[0076] Table 1 Effects of different millet addition amounts on the color of recombined rice

[0077]

[0078] From Table 1 and Figure 2It can be seen that the color of the recombined rice after adding millet shows an obvious gradient change compared with that of rice. The L* value decreases with the increase of the millet addition amount, while the a* and b* values show an upward trend. This indicates that with the addition of millet, the transparency and brightness of the recombined rice decrease. The change of the a* value reflects that the red-green tone of the recombined rice changes from the original greenish tone to a reddish tone, while the b* value indicates that the recombined rice also tends to a yellowish tone. This is due to the red-yellow color and relatively low transparency of millet itself, which makes the recombined rice with different millet addition amounts show a gradient color change trend. This color change not only affects the visual attractiveness of the recombined rice but also has an impact on consumers' acceptance. Color is an important part of the sensory characteristics of food, and consumers often judge the quality and taste of food based on its appearance. Appropriate addition of millet may improve the overall appearance of the recombined rice and increase its market competitiveness. However, excessive addition of millet may lead to overly dull color, which in turn affects consumers' willingness to purchase. Therefore, it is crucial to reasonably control the addition amount of millet to ensure a balance between the nutrition and sensory characteristics of the recombined rice.

[0079] 3. Determination of cooking characteristics

[0080] (1) Determination of cooking loss rate

[0081] Weigh 3.00 g (m0) of the sample into a 100 mL beaker, add 50 mL of distilled water, take it out after boiling water bath for 10 min, pour the rice soup into a beaker that has been weighed to a constant weight (m1), and dry it to a constant weight (m2) at 105 °C. Repeat the determination 3 times and take the average value.

[0082] The cooking loss rate is calculated by the following formula:

[0083] Cooking loss rate (%) = [(m2 - m1) / m0] × 100%

[0084] (2) Determination of water absorption rate

[0085] Weigh 5.00 g (m0) of the sample into an aluminum box, add 20 mL of pure water, steam it in a steamer for 10 min; after cooling, transfer it to a centrifuge tube that has been weighed to a constant weight (m1) for centrifugation, and weigh the total mass of the centrifuge tube and the precipitate (m2). Repeat the determination 3 times and take the average value.

[0086] The water absorption rate is calculated by the following formula:

[0087] Water absorption rate (%) = [(m2 - m1) / m0] × 100%

[0088] (3) Determination of swelling ratio

[0089] Weigh 5.00 g (m0) of the sample into a graduated test tube, record the volume V1, add 5 mL of pure water, place it in a steamer and steam for 10 min, then put it back into the graduated test tube and record the volume V2. Repeat the measurement 3 times and take the average value.

[0090] The swelling rate is calculated by the following formula:

[0091] Swelling rate (mL / g) = (V2 - V1) / m0 × 100%

[0092] The test results are shown in Table 2.

[0093] Table 2 Effects of different millet addition amounts on the cooking properties of recombinant rice

[0094]

[0095]

[0096] To evaluate the effects of different millet addition amounts on the eating quality of recombinant rice, the cooking loss rate, water absorption rate, and swelling rate of recombinant rice were measured. It can be seen from Table 2 that as the millet addition amount increases, the cooking loss rate of recombinant rice is lower than that of rice (7.11 ± 1.10%), and the cooking loss rate of recombinant rice with 80% millet addition is the lowest, only 3.54 ± 0.15%. The lower cooking loss rate indicates that recombinant rice is more stable during cooking, which helps to reduce the phenomenon of rice crumbling and soupiness, thus improving the taste.

[0097] Although there were no significant differences in the water absorption rate and swelling rate of recombinant rice with the change of millet addition amount, indicating that the influence of millet addition on these two indicators is relatively limited. However, the swelling rates of recombinant rice with 60% and 80% millet addition (43.16 ± 11.5%, 43.16 ± 8.27%) both exceeded 43%, higher than that of rice (39.74 ± 9.83%), improving the texture and volume feeling of the rice. Generally speaking, appropriate addition of millet can not only reduce the loss during cooking, but also may help to optimize the taste and texture of the rice.

[0098] 4. Determination of texture properties

[0099] Take 100 g of recombinant rice and place it in a 250 mL beaker. Soak the recombinant rice according to a rice-to-water ratio of 1:1.5. Let the recombinant rice cool slightly, place the beaker on the operating table, ensure that the probe is in the middle of the rice, and then start the test. Set the test conditions of the texture analyzer as follows: P100 probe, deformation amount: 50%; pre-test rate: 1 mm / s; test speed: 1 mm / s; starting force: 0.5 N. Repeat 6 times under the same conditions and calculate the average value.

[0100] The results are shown in Table 3.

[0101] Table 3 Effects of Different Millet Addition Amounts on the Texture Properties of Recombinant Rice

[0102]

[0103] The texture properties of recombinant rice not only affect its taste but also are directly related to the digestion process, and are important indicators for evaluating its edible quality and consumer acceptance. As can be seen from Table 3, there are significant differences in the texture of recombinant rice with different millet addition amounts. Among them, the hardness, elasticity, cohesiveness, adhesiveness, and chewiness of rice are all the highest, indicating that its texture is relatively hard and the digestion rate is relatively slow. With the increase of the millet addition amount, all texture indexes show a significant downward trend (p<0.05). Especially when the millet addition amount is 40%, the hardness drops to 47.31±11.09, indicating that the recombinant rice is softer, easier to chew and digest, thus helping to improve the absorption rate of nutrients. In addition, the adhesiveness and chewiness of the recombinant rice with 60% millet addition amount are the lowest, which are 14.42±5.22 and 118.7±57.92 respectively. This means that the rate of starch release during the digestion process of the recombinant rice decreases, thus helping to maintain blood sugar levels. The lower chewiness indicates that the recombinant rice is softer in taste and easier to chew, which is suitable for consumers who are sensitive to the texture of food, especially the elderly or those with weak digestive ability.

[0104] In summary, appropriate millet addition not only improves the texture properties of recombinant rice but also enhances its digestibility and health benefits. By adjusting the addition ratio of millet, it is possible to improve nutrient absorption and reduce the digestive burden while maintaining a good taste.

[0105] 5. Microstructure Analysis

[0106] (1) SEM Morphology Scanning

[0107] Fix the dry and anhydrous recombinant rice grains on a metal sample platform with conductive double-sided tape, and after vacuum spraying with gold, place them under a scanning electron microscope to take pictures. The test voltage is 10 KV and the magnification is 3000 times. The SEM morphology scanning diagrams of recombinant rice with different millet addition amounts are shown in Figure 3 .

[0108] The microscopic structural characteristics of the rice samples can be observed through a scanning electron microscope. As can be seen from Figure 3 , the surfaces of rice (a) and millet (f) are complete and smooth. The starch granules of the recombinant rice with 20% and 40% millet addition amounts (b, c) are damaged, and there are irregular cracks on the surface of the rice grains. This is because the cell walls are damaged and the starch structure changes due to the action of high temperature, high pressure, and high shear force during the extrusion process. However, there are no obvious changes on the surfaces of the recombinant rice with 60% and 80% millet addition amounts. This may benefit from the high content of millet addition, which makes its surface structure not damaged.

[0109] (2) X-ray diffraction

[0110] The dried instant rice samples were ground and sieved, and the crystal structures of different miscellaneous grain recombined rice were determined using a Bruker D8 type X-ray diffractometer (XRD). The test conditions were as follows: Cu-Kα ray, scanning speed of 2 °C / min, continuous scanning, repeated 3 times. The effects of different millet addition amounts on the XRD of the recombined rice are shown in Figure 4 .

[0111] The long-range ordered structure of starch can be evaluated by X-ray diffraction, thereby reflecting the degree of starch aging and crystal form. According to the differences in the XRD patterns, starch can be divided into different crystal forms: the diffraction peaks of type A crystals are at 15°, 17°, 18°, and 23°; the diffraction peaks of type B crystals are at 5.6°, 17°, 22°, and 24°; the diffraction peaks of type V crystals are at 7.4°, 13°, and 20°. The XRD patterns of all samples are as shown in Figure 4 . It can be seen from the figure that commercial rice has a diffraction peak at 15.1°, which is a typical diffraction characteristic of type A crystals. After recombination, the diffraction peaks show obvious deviations. Both the recombined rice and millet have large characteristic single peaks at 13° and 19.8°, and a smaller diffraction peak at 7.5°, which belong to typical type V crystals. This indicates the presence of starch-lipid complexes in the recombined rice and millet. The formation of starch-lipid complexes can hinder the action of digestive enzymes on starch, thereby slowing down the digestion rate. Therefore, compared with ordinary rice, the recombined rice containing starch-lipid complexes may have a lower blood glucose response and contribute to maintaining a stable blood glucose level, but different addition amounts have no obvious effect on the crystal form of the recombined rice.

[0112] 6. Sensory property analysis

[0113] Referring to GB / T 15682-2008 "Inspection of grain and oils - Sensory evaluation method for cooking and eating quality of paddy and rice", 10 trained food professionals, with an average age of 25 years old (5 males and 5 females), were used as sensory evaluation personnel to evaluate the sensory scores of the recombined rice. The sensory evaluation criteria are shown in Table 4. The evaluation results are shown in Figures 5 - 6 .

[0114] Table 4 Sensory evaluation criteria

[0115]

[0116] The recombined rice with different millet addition amounts was subjected to sensory evaluation, and the scoring results are as shown in Figures 5 - 6 . The results show that the recombined rice with 60% millet addition amount performed best in terms of palatability, softness and hardness, appearance structure, and color, and obtained the highest score.

[0117] With the further increase in the amount of millet added, the total sensory evaluation score gradually decreased, indicating that excessive addition of millet would affect the overall eating texture of the cooked rice. When the amount of millet added was less than 60%, the total sensory evaluation score of the cooked rice showed a certain upward trend. Compared with traditional rice products, the sensory score of 60% reconstituted millet rice increased by 9.3%, and the palatability increased by 3.6%. This result indicates that the sensory characteristics of pure rice and millet are inferior to those of reconstituted millet rice with a reasonable ratio. The research results show that appropriate addition of millet can not only improve the sensory quality of the cooked rice but also contribute to promoting diverse choices of staple foods.

[0118] 7. Rapid and slow digestible starch

[0119] Take 1 g of the reconstituted rice sample and place it in a 50 mL centrifuge tube. Add 20 mL of sodium acetate buffer (pH = 5.2, 0.1 M), preheat it in a water bath at 37 °C for 20 min. Take out 1 mL of the supernatant and filter it through a membrane. Use a UV spectrophotometer to carry out the DNS reaction and measure the absorbance at a wavelength of 540 nm. Calculate the glucose content according to the DNS standard curve, which is G0. Add 0.1 mL of α-amylase and 0.5 mL of amyloglucosidase to the centrifuge tube. After enzymatic hydrolysis for 20 and 120 min respectively, take 1 mL of the enzymatic hydrolysis solution each time, add 4 mL of absolute ethanol to inactivate the enzyme, centrifuge (3000 r / min, 10 min), take out 1 mL of the supernatant and filter it through a membrane, carry out the DNS reaction, and measure the absorbance at a wavelength of 540 nm. Calculate the glucose content according to the DNS standard curve, and obtain G20 and G120. The starch digested within 20 min of enzymatic hydrolysis is called rapidly digestible starch, i.e., RDS. The starch digested within 20 - 120 min is called slowly digestible starch, i.e., SDS. The starch digested after enzymatic hydrolysis for more than 120 min is called resistant starch, i.e., RS.

[0120] RDS% = 0.9×(G20 - G0) / mass of the sample × 100%

[0121] SDS% = 0.9×(G120 - G0) / mass of the sample × 100%

[0122] RS% = TS% - RDS% - SDS%

[0123] In the formula: G0, G20, and G120 represent the glucose contents at 0 min, 20 min, and 120 min of enzymatic hydrolysis respectively; 0.9 is the conversion coefficient.

[0124] The measurement results are shown in Figure 7 .

[0125] Through in vitro simulated digestion experiments, the contents of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) of each sample were determined. AsFigure 7 As shown, the in vitro digestion results indicate that the RDS of the recombinant rice with 60% millet addition is the highest, reaching 71.26 ± 1.08%, while the SDS is the lowest, only 7.67 ± 2.93%, and the RS content is also relatively low, 21.06 ± 2.14%.

[0126] This shows that the digestibility of the recombinant rice with 60% millet addition has been significantly improved because the appropriate addition of millet promotes the rapid digestion of starch. In contrast, when the millet addition increases to 80%, the RDS content drops to the lowest (59.31 ± 2.53%), while the RS content significantly rises to 26.56 ± 7.97%. This indicates that the recombinant rice with 80% millet addition exhibits stronger anti-digestibility, which is because the excessive millet makes the starch structure more compact, reducing the binding sites of digestive enzymes and further restricting the penetration of starch granules to reduce the starch digestibility. Rice with a high RDS content can usually quickly provide energy and is suitable for situations where rapid energy replenishment is needed; while a high RS content helps improve intestinal health and promote satiety.

[0127] In summary, different millet addition amounts significantly affect the digestion characteristics of the recombinant rice, and reasonable control of the addition amount can achieve a balance between meeting taste and nutritional requirements.

[0128] 8. Fatty Acid Determination

[0129] Weigh 0.1 g of the sample into a 50 mL centrifuge tube, add approximately 100 mg of pyrogallic acid, then add 2 mL of 95% ethanol and 4 mL of water, mix well, and add 10 mL of 8.3 mol / L hydrochloric acid (250 mL hydrochloric acid + 110 ml water), and mix well. Place the centrifuge tube in a water bath at 70 - 80 °C for hydrolysis for 40 min, shake the centrifuge tube every 10 min to mix the particles sticking to the centrifuge tube wall into the solution. After hydrolysis is completed, cool to room temperature. For the hydrolyzed sample, add 10 ml of 95% ethanol, mix well, add 20 ml of petroleum ether, shake for 5 min, and let stand for 15 min to extract the fatty acids. Collect the organic phase in another new 50 mL centrifuge tube and repeat the operation 3 times. Evaporate the organic phase in a water bath at 70 °C to dryness, and the residue is the fat extract for further determination.

[0130] In the fat extract, add 8 ml of 2% sodium hydroxide methanol solution (dissolve 2 g of sodium hydroxide in 100 ml of methanol), seal and heat at 80 °C until the oil droplets disappear. Add 1.75 mL of boron trifluoride methanol (55% - 60%) solution, then add 5.55 mL of methanol, continue to heat for 2 min, stop heating, and cool to room temperature. Take 2 ml of n-hexane for extraction, add 5 mL of saturated brine until the extraction layer is completely separated, let stand for layering for more than 30 min, and measure the n-hexane layer on the machine.

[0131] Gas chromatography conditions: Chromatographic column: HP-88 chromatographic column, inlet temperature 240 °C, detector temperature 240 °C, initial temperature of the column oven 130 °C, heated to 240 °C at a rate of 4 °C / min and maintained for 20 min. Hydrogen flow rate 30 mL / min, air flow rate 400 mL / min, injection volume 1 μL.

[0132] The measurement results are shown in Figure 8 .

[0133] Fatty acids are key substances for human life activities. By measuring the fatty acid content in recombinant rice, the impact of different millet addition amounts on the nutritional value of recombinant rice can be further evaluated. As Figure 8 can be seen, among all samples, the content of linoleic acid is the highest, followed by palmitic acid, oleic acid, stearic acid and linolenic acid. With the increase of the millet addition amount, the contents of palmitic acid, stearic acid and oleic acid all increase. When the millet addition amount is 60%, the linoleic acid content in the recombinant rice shows a significant increase compared with the rice sample. Compared with traditional rice products, the linoleic acid in fatty acids has increased by 107.80%.

[0134] As an unsaturated fatty acid, linoleic acid can promote the degradation of cholesterol into bile acids and excrete them from the body, thereby reducing the body's cholesterol level. The appropriate addition of millet can not only increase the content of linoleic acid in recombinant rice, but also improve its overall fatty acid composition, making the recombinant rice have better lipid-lowering potential. This result indicates that a reasonable millet addition ratio can maintain the texture of the food while enhancing its positive impact on health, especially in regulating blood lipids and promoting blood circulation. Good regulation of blood lipids is an important factor in preventing cardiovascular diseases, especially atherosclerosis. Therefore, the addition of 60% millet can provide more effective health benefits.

[0135] 9. Determination of moisture distribution

[0136] The transverse relaxation time was measured by a low-field nuclear magnetic resonance spectrometer to analyze the moisture distribution and migration of recombinant rice. Take 2 g of the recombinant rice sample and place it in a centrifuge tube, and then place the centrifuge tube in the nuclear magnetic resonance detection chamber for detection. Detection parameters: main frequency (MHz) = 21, sampling frequency (kHz) = 250, echo time (ms) = 0.20000, number of echoes = 8000, number of repeated scans (ns) = 12, relaxation time points = 100, temperature 30 °C.

[0137] The measurement results are shown in Figure 9 .

[0138] The moisture distribution will affect the interaction between the components in the recombinant rice and affect the final quality of the recombinant rice. As Figure 9 can be seen, the T2 inversion spectra of the low-field nuclear magnetic resonance (LF-NMR) of each sample have two peaks, which are T 21 and T22 , indicating that there are two different moisture states in the recombinant rice. T 21 is the relaxation time of strongly bound water, which refers to the water strongly bound to macromolecules and is the main form of water existence in recombinant rice. T 22 is the relaxation time of weakly bound water, which refers to the weakly bound water indirectly bound to macromolecules and directly bound to strongly bound water by hydrogen bonds. As the addition amount of millet gradually increases, the relaxation time gradually decreases, indicating that the mobility of water molecules in the recombinant rice decreases and it has good water retention. This is because water molecules form an ordered structure with starch during the extrusion process, thus reducing the migration rate of water molecules. This property is beneficial to the long-term storage of recombinant rice.

[0139] In addition, as the addition amount of millet increases, T 22 also gradually decreases, indicating that there is a tendency for weakly bound water in the recombinant rice to migrate to strongly bound water. Free water was not detected in each recombinant rice sample due to the loss of free water during sample preparation.

[0140] 10. Amino acid determination

[0141] Referring to the national standard GB5009.124-2016 Determination method of amino acids in foods, chromatographic column: sulfonic acid type cation resin; detection wavelengths: 570 nm and 440 nm.

[0142] The determination results are shown in Figure 10 .

[0143] The amino acid composition of each recombinant rice is as Figure 10 shown. The results show that the sample contains 6 essential amino acids and 10 non-essential amino acids. Among them, the contents of 5 amino acids (threonine, phenylalanine, valine, leucine, isoleucine) in millet are higher than those in rice, and as the addition amount of millet increases, the contents of these 5 amino acids show an increasing trend. In all samples, the content of glutamic acid is the highest. Abundant glutamic acid can improve exercise and immune capabilities, and also has the functions of promoting brain development and regulating the formation of the cytoskeleton.

[0144] As the addition amount of millet increases, the content of glutamic acid also shows an increasing trend. Compared with traditional rice products, the content of glutamic acid in amino acids has increased by 39.82%, indicating that a higher proportion of millet addition significantly increases the amino acid content in the recombinant rice, thus further enriching the nutritional value of the recombinant rice.

Claims

1. A method for preparing recombinant rice based on millet, characterized in that: The following steps are involved: S1. preparing rice and millet, wherein the millet accounts for 20%-80% of the total mass of the rice and millet; S2, crushing the prepared rice and millet, then sieving and mixing to obtain mixed rice flour; S3, putting the mixed rice flour into a twin-screw extruder, using the twin-screw extruder to extrude and ripen the mixed rice flour, and cutting and granulating the mixed rice flour to obtain reconstituted rice grains; S4, drying and cooling the recombinant rice grains to obtain a recombinant rice product.

2. The method for preparing recombinant rice based on millet according to claim 1, characterized in that: The millet accounts for 55%-65% of the total mass of rice and millet.

3. The method for preparing recombinant rice based on millet according to claim 1, characterized in that: The millet accounts for 60% of the total mass of rice and millet.

4. The method for preparing recombinant rice based on millet according to claim 1, characterized in that: The sieving in step S2 is through a 70-90 mesh sieve.

5. The method for preparing recombinant rice based on millet according to claim 1, characterized in that: The parameters of the twin-screw extruder in step S3 are set as follows: feeding rate 120-180g / min, material water addition amount 34-38%, screw speed 120-180r / min, extrusion temperature in zone II 75-85°C, extrusion temperature in zone III 82-88°C, extrusion temperature in zone IV 82-88°C, extrusion temperature in zone V 88-92°C, extrusion temperature in zone VI 88-92°C, and cutter speed 1400-1600r / min.

6. The method for preparing recombinant rice based on millet according to claim 1, characterized in that: The parameters of the twin-screw extruder in step S3 are set as follows: feeding rate 150g / min, material water addition amount 36%, screw speed 150r / min, extrusion temperature in zone II 80°C, extrusion temperature in zone III 85°C, extrusion temperature in zone IV 85°C, extrusion temperature in zone V 90°C, extrusion temperature in zone VI 90°C, and cutter speed 1500r / min.

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