Method for making all-black rice with high softness and stickiness

Abstract

The application discloses a kind of whole black rice high soft glutinous degree production methods, it is related to whole black rice production technical field, first to selected black rice is removed and cleaned, remove surface dust and shriveled grain residual grain, then the black rice after cleaning is placed in gradient temperature control environment subsection swelled, accurately control the ambient temperature, relative humidity and processing time length of each swelling stage, make moisture gradually penetrate to black rice endosperm inside, and ensure that black rice outer layer fiber skin layer remains intact without damage;Swelling is completed using stage type variable pressure cooking process, sequentially through normal pressure preheating, micro high pressure gelatinization, three stages of normal pressure stewing complete black rice starch sufficient gelatinization.The whole black rice prepared by the application does not need to be polished in advance to remove the outer skin layer, can retain the original anthocyanins, dietary fiber and other functional components of black rice, has low GI value, good soft glutinous taste and high rice kernel integrity, slow starch retrogradation speed, no significant taste attenuation after cold storage and reheating.

Description

Technical Field

[0001] This invention relates to the field of black rice production technology, and more particularly to a method for producing black rice with high softness and glutinousness. Background Technology

[0002] As a whole grain staple food with high dietary fiber and low GI, whole black rice is widely used in light meals, sugar-controlled meals, and ready-to-eat staple foods. In recent years, with the improvement of people's awareness of healthy eating, the market demand for whole black rice, which has good taste, intact shape, stable storage and original nutritional properties, has continued to grow.

[0003] Currently, the mainstream processes for preparing whole black rice fall into two categories. The first is a long-term cooking process under normal pressure. Its working principle involves continuous high-temperature cooking at normal pressure for 1-2 hours, causing water to slowly penetrate the dense, coarse-fiber outer layer of the black rice, achieving full gelatinization of the endosperm starch and resulting in a soft and glutinous texture. This process requires no special equipment, has a low operational threshold, and is widely used in home consumption and small-scale catering settings, retaining most of the original nutrients of the black rice without the need for additional ingredients. However, this process has a long cooking cycle, and prolonged high-temperature heating can easily cause the black rice outer layer to crack and the endosperm to overflow, resulting in a low percentage of intact rice grains. It also suffers from problems such as a mushy broth and rice grains sticking together. Furthermore, there is no corresponding anti-retrogradation treatment; after the finished product is left at room temperature for 4 hours or refrigerated for 1 day, significant starch retrogradation occurs, resulting in a hard and gritty texture, making it unsuitable for industrial production and long-distance distribution.

[0004] The second type is the industrial milling pretreatment + high-pressure cooking process. Its working principle involves first physically milling to remove 20%-40% of the outer layer of black rice, reducing water penetration resistance, and then cooking at 0.1-0.2 MPa for 15-30 minutes to achieve rapid starch gelatinization, significantly improving production efficiency. The initial finished product has a soft and glutinous texture, suitable for large-scale mass production, and is currently the mainstream production process for ready-to-eat black rice staple foods. However, this process of milling to remove the outer layer causes a significant loss of functional components such as anthocyanins and dietary fiber, raising the GI value of the finished product to over 55, thus losing the original low-GI nutritional advantage of black rice. Furthermore, the high-pressure cooking process still easily leads to rice grain expansion and cracking, making it difficult to balance softness and glutinousness with the integrity of the grain shape. Moreover, no effective control measures are taken against starch retrogradation, resulting in a significant decrease in taste after reheating after refrigeration, failing to meet the quality requirements of high-end ready-to-eat staple foods.

[0005] With the rapid development of the ready-to-eat pre-made staple food market, existing processes can no longer simultaneously meet consumers' multiple requirements for the taste, appearance, nutrition, and storage properties of whole black rice. The industry urgently needs to develop a whole black rice preparation process that is suitable for industrial production to solve the core pain points of existing technologies. Summary of the Invention

[0006] To address the problems of difficulty in achieving both softness and integrity in existing whole-black rice, easy starch retrogradation, and increased glycemic index due to nutrient loss in the bran, this invention provides a method for producing whole-black rice with high softness and glutinousness.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for producing highly soft and glutinous all-black rice, belonging to the field of grain deep processing technology, including the following steps:

[0008] S1. Enzymatic softening of the outer layer: Select first-grade edible black rice that meets the requirements of NY / T832 standard, place it in warm water with added cellulase and hemicellulase for constant temperature soaking, and degrade the coarse fiber cross-linking structure of the dense outer layer of black rice through enzymatic hydrolysis to achieve uniform softening of the black rice outer layer.

[0009] S2, Calcium Salt Crosslinking and Shaping: Add compound calcium salt, which is composed of calcium lactate and calcium gluconate, to the black rice soaking system after enzyme soaking. Keep warm and let stand so that calcium ions can penetrate into the black rice bran and surface endosperm, and react with polysaccharide components to enhance the stability of rice grain structure and achieve rice grain morphology shaping.

[0010] S3. High-pressure synergistic gelatinization: After the black rice has been treated with calcium salts, drain it and add drinking water, baking soda, edible salt, and edible salad oil according to the set ratio. At the same time, add a compound anti-retrogression component, which is composed of trehalose and soluble soybean polysaccharide. After all materials are mixed evenly, they are placed in a high-pressure environment for cooking to fully gelatinize the black rice starch and achieve a soft and glutinous texture.

[0011] S4. Cooling and Packaging: After the cooked black rice is subjected to gradient rapid cooling, it is sealed and packaged in a sterile and clean environment to obtain a finished product of highly soft and glutinous black rice.

[0012] Furthermore, the process parameters for constant-temperature soaking in S1 are as follows: the temperature of the soaking water is stably controlled at 35-45℃. This temperature range is the optimal operating temperature range for cellulase and hemicellulase, ensuring enzymatic hydrolysis efficiency while avoiding enzyme inactivation due to high temperatures. It also prevents premature gelatinization and stickiness of the starch on the surface of the black rice, which would affect subsequent processing. The mass ratio of the dry weight of the black rice to the warm water in the soaking system is 1:1.2-1:1.8, with the liquid level 2-3 cm above the black rice stack to ensure that all black rice is fully submerged in the enzyme solution, avoiding uneven enzymatic hydrolysis caused by localized dry cores. The cellulase used has an activity of 10000 U / g, and the amount added is 0.0% of the dry weight of the black rice. The enzyme content is 2%-0.06%, and the activity of the hemicellulase used is 8000U / g. The amount added is 0.01%-0.03% of the dry weight of black rice. The combination of the two enzymes can specifically degrade the cross-linked cellulose and hemicellulose components in the bran of black rice, cut off the dense network structure of the coarse fiber in the bran, and will not over-decompose the bran, thus reducing the integrity of the rice grains. The total soaking time at constant temperature is 2-4 hours. During the soaking period, the soaking system is lightly stirred once every 30 minutes. The stirring intensity should be such that it does not cause mechanical damage to the rice grains, promotes the flow of enzyme solution between rice grains, ensures that all rice grain brans are uniformly enzymatically hydrolyzed, and avoids the problem of hard core in the finished product caused by insufficient softening of the local bran.

[0013] Furthermore, the amount of compound calcium salts added in S2 is based on the total mass of the soaking solution. The amount of calcium lactate added is 0.08%-0.15%, and the amount of calcium gluconate added is 0.04%-0.08%. The combination of the two calcium ion sources can take into account both the dissociation rate and the penetration depth of calcium ions. Among them, calcium lactate has a fast dissociation rate and can quickly cross-link with the pectin and hemicellulose degradation products on the outermost layer of rice grains, forming a stable cross-linked network structure on the surface of rice grains. Calcium gluconate has a stronger penetrating ability and can gradually penetrate into the endosperm tissue 1-2 mm below the surface of rice grains, interacting with the endosperm in the surface layer. The starch and polysaccharide components undergo weak cross-linking, strengthening the surface endosperm structure and preventing sticky, clumped, and poorly shaped rice caused by the rupture of the rice grain skin and endosperm overflow during subsequent high-pressure cooking. After the calcium salt is added, the soaking system temperature is maintained at 35-45℃, and the rice is kept warm and allowed to stand for 15-30 minutes without vigorous stirring to avoid damaging the cross-linking structure forming on the surface of the rice grains. This allows calcium ions sufficient time to penetrate into the rice grain tissue and complete the cross-linking, forming a rice grain surface structure that is soft on the outside and tough on the inside, providing structural support for the morphological integrity during high-pressure cooking.

[0014] Furthermore, the mass ratio of drained black rice to drinking water in S3 is 1:1.1-1:1.5. This rice-to-water ratio ensures that the black rice obtains sufficient water to complete starch gelatinization during high-pressure cooking, without causing the rice to become too sticky and lose its elastic texture due to excessive water. The ratio can be slightly adjusted within this range according to the initial moisture content of different batches of black rice. When the initial moisture content is below 13%, the amount of water added should be increased appropriately, and when it is above 14.5%, the amount of water added should be decreased appropriately. The amount of baking soda added is 0.05%-0.15% of the dry weight of black rice. Its weak alkalinity can neutralize the acidic components in the black rice bran, weaken the binding force between the bran fiber and starch, and promote the starch to fully absorb water and gelatinize during cooking. At the same time, the moderately alkaline environment can reduce the degradation of anthocyanins in the black rice bran and maintain the color and nutritional activity of the finished product.

[0015] The amount of salt added is 0.1%-0.3% of the dry weight of black rice. The trace amount of salt can bring out the natural aroma of the black rice without a noticeable salty taste. It can also strengthen the cross-linked structure of the rice grain surface through ionic action, reducing rice grain breakage during cooking. The amount of salad oil added is 0.3%-0.8% of the dry weight of black rice. It can form a uniform thin oil film on the surface of the rice grains, reducing direct adhesion between rice grains, reducing the risk of foam overflow during cooking, and improving the gloss of the cooked rice. After adding all the ingredients, stir at a low speed of 30-60 r / min in the same direction for 2-3 minutes to ensure that all materials are evenly mixed with the black rice, without local powder agglomeration or uneven moisture distribution. The stirring process avoids high-speed shearing that could cause mechanical damage to the rice grains.

[0016] Furthermore, the amount of trehalose added in S3 is 1%-3% of the dry weight of black rice, and the amount of soluble soybean polysaccharide added is 0.5%-1.5% of the dry weight of black rice. The combination of the two anti-retrogradation components can inhibit starch retrogradation from different levels. Trehalose is a small molecule disaccharide that can penetrate into the interior of starch granules and form hydrogen bonds with starch molecules, reducing the probability of starch molecules rearranging and forming dense crystals during cooling. Soluble soybean polysaccharide is a large molecule hydrophilic polysaccharide that can form a stable hydrophilic film on the surface of gelatinized starch molecules, preventing starch molecules from approaching each other and rearranging, while improving the water retention of rice and reducing moisture loss during refrigeration.

[0017] Before adding trehalose and soluble soybean polysaccharides, stir them in an appropriate amount of drinking water at 40-50℃ until completely dissolved. Then add them to the black rice along with the other ingredients. This avoids problems such as clumping and uneven distribution of powder caused by directly adding dry powder, and prevents local rice from having insufficient anti-retrogradation effect, or being too sweet or sticky. It ensures that the anti-retrogradation components are evenly distributed on the surface of the rice grains and in the cooking liquid. During the cooking process, they penetrate into the interior of the rice grains with the water, achieving a uniform anti-retrogradation effect and avoiding local differences in taste in the finished product.

[0018] Furthermore, the process parameters for high-pressure cooking in S3 are as follows: the high-pressure cooking equipment uses a commercial pressure cooker with electric heating or steam heating, and the internal pressure is stably controlled at 40-60 kPa, corresponding to a cooking temperature of 110-120℃. Compared with the cooking conditions of 100℃ under normal pressure, under this temperature and pressure condition, water can penetrate into the black rice endosperm more quickly, allowing the starch to be fully gelatinized in a shorter time, and the starch granules to expand more evenly. This avoids the problems of excessive surface gelatinization and insufficient internal gelatinization caused by prolonged heating during normal pressure cooking. At the same time, the high-pressure environment can accelerate the further softening of the outer layer fiber after enzymatic hydrolysis, improving the softness and glutinousness of the finished product.

[0019] Once the equipment reaches the set pressure and temperature, maintain constant pressure and temperature for cooking for 30-50 minutes. The cooking time can be slightly adjusted according to the age of the black rice. For black rice stored for more than 6 months, extend the cooking time by 5-10 minutes, and for new black rice from the current year, shorten the cooking time by 5 minutes. Do not manually release air during the entire cooking process to maintain stable temperature and pressure inside the pot and avoid large pressure fluctuations that could cause the rice grains to collide and break, thus ensuring uniform and stable starch gelatinization.

[0020] Furthermore, the specific steps of gradient rapid cooling in S4 are as follows: After high-pressure cooking, the pressure inside the equipment is first naturally released to reduce to atmospheric pressure. The pressure release time is controlled at 8-12 minutes to avoid a sudden drop in pressure caused by rapid pressure release, which could cause the internal moisture of the rice grains to vaporize and break through the skin. After depressurization, the lid is opened, and the black rice is evenly spread on a sterile, breathable tray with a layer thickness of 2-3 cm. This avoids the risk of retrogradation due to an excessively thick layer or a layer that is too thin, which could lead to surface moisture loss and hardening. After spreading, the rice is first cooled with 0.22... The sterilization process using a μm filter membrane at room temperature reduces the core temperature of the rice to 60-70℃, reducing excessive softening of starch at high temperatures and maintaining the elasticity of the rice grains. The rice is then transferred to a sterile cooling room at 18-22℃ and 60%-70% relative humidity, where vertical laminar flow clean air reduces the core temperature to 20-25℃, and humidity is controlled to prevent the rice grains from forming a crust. The entire cooling process takes no more than 40 minutes, quickly passing through the temperature range where starch easily retrogrades, reducing starch rearrangement and crystallization. Gradual cooling prevents the rice grains from shrinking due to sudden cooling, ensuring uniform softness and glutinous texture.

[0021] Furthermore, before the S1 enzymatic softening step, a pre-treatment process for black rice is included: the raw black rice is screened through a double-layer vibrating screen to remove sand, shriveled grains, and foreign impurities. The upper screen has a mesh size of 5mm, and the lower screen has a mesh size of 2mm to remove large-sized impurities and small-sized broken rice and shriveled grains, thereby improving the uniformity of the raw materials. After screening, the rice is quickly rinsed 1-2 times with room temperature running drinking water. Each rinsing time should not exceed 30 seconds, and the water flow speed should be such that the rice grains are slowly turned over to avoid excessive water flow impact that could damage the skin. After rinsing, drain the surface water using a 30-mesh strainer for 2-3 minutes until no obvious water droplets fall, then proceed to the enzyme soaking process. Avoid vigorously rubbing the rice grains during rinsing. Since the functional components of black rice, such as anthocyanins and dietary fiber, are mainly distributed in the outer layer, excessive rinsing will cause the loss of the outer layer, resulting in nutrient loss and a decrease in dietary fiber content, which will increase the glycemic index of the finished product and make it impossible to maintain the original low-GI characteristics of black rice. Quick rinsing only removes surface dust and free impurities, which can retain the nutrients and functional components of the outer layer to the maximum extent.

[0022] Furthermore, after the high-pressure cooking time reaches the set cooking time, the heating source is immediately cut off, and the high-pressure equipment is kept in a sealed state for simmering for 5-10 minutes. During the simmering process, no pressure is released or the lid is opened. The residual heat and pressure inside the pot are used to slowly act on the rice grains, allowing the internal moisture and heat to be fully and evenly conducted. During the high-pressure cooking stage, the starch gelatinization degree on the surface of the rice grains is slightly higher than that of the internal endosperm. Through sealed simmering, the surface moisture can gradually penetrate into the interior, and the internal starch can be further gelatinized under the action of residual heat. Ultimately, the degree of gelatinization of the rice grains is uniform from the outside to the inside, avoiding the problem of insufficient homogeneity, such as the rice grains being too soft on the surface and hard in the core. During the simmering process, the temperature inside the pot is slowly reduced by 10-15°C, which can reduce the temperature difference in the subsequent cooling steps, reduce the probability of structural shrinkage of the rice grains due to sudden cooling, and further improve the uniformity of the finished product's texture.

[0023] Furthermore, the resulting high-softness, glutinous black rice product has a grain integrity rate of no less than 90%, with no issues of rice clumping or sticking to the bottom; after refrigeration at 4℃ for 7 days, the starch retrogradation rate is no higher than 15%, demonstrating excellent anti-aging effects and suitability for refrigerated storage and distribution; the finished product has a glycemic index of no more than 55, classifying it as a low-GI food, meeting the dietary needs of people with blood sugar control; after reheating in a microwave or boiling water bath for 3-5 minutes, it still maintains a soft, glutinous, and elastic texture, without significant retrogradation, hardening, or clumping, meeting the production and distribution needs of industrialized ready-to-eat black rice.

[0024] The present invention has the following beneficial effects:

[0025] This invention utilizes a gradient temperature-controlled swelling and staged variable pressure cooking technique to allow water to fully penetrate the black rice endosperm without pre-grinding or removing the outer skin. This ensures that the starch is fully gelatinized to achieve an ideal soft and glutinous texture, while avoiding endosperm overflow and rice grain sticking caused by damage to the outer skin. This significantly improves the integrity of the finished rice grains and also preserves the anthocyanins, dietary fiber, and other functional active components of the black rice outer skin. This effectively solves the shortcomings of existing technologies that cannot simultaneously achieve a soft and glutinous texture, intact rice grain shape, and low-GI nutritional properties.

[0026] This invention uses a combination of gradient cooling conditioning after cooking and ultrasound-assisted stabilization to inhibit the recrystallization tendency of starch molecules after gelatinization, delay the starch retrogradation process, and avoid the problem of hardening and gritty texture during the storage of the finished product. After reheating, the taste is not significantly different from that of the newly made product, effectively solving the defects of the existing technology, which lacks a matching anti-retrogradation treatment, resulting in poor storage stability of the finished product and insufficient adaptability for long-distance circulation.

[0027] The entire process of this invention requires no additional food additives, all operating parameters can be standardized and controlled, batch production has good stability, no need to customize special production equipment, can be directly connected to existing staple food industrial production lines, effectively reducing equipment modification costs at the production end, and adapting to the needs of large-scale industrial production.

[0028] The whole black rice prepared by this invention can be widely used in various consumption scenarios such as freshly prepared catering products, ready-to-eat staple foods at room temperature, and frozen staple foods. It is also suitable for the consumption needs of ordinary healthy people and people with blood sugar control needs. There is no need to adjust the core process parameters for different application scenarios. The process has strong adaptability and has high industry promotion value. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating a method for producing highly soft and glutinous all-black rice according to the present invention.

[0030] Figure 2 The instant processing quality grouped bar chart of ready-to-eat black rice in this invention;

[0031] Figure 3 The anti-retrogression performance grouped by bar chart for 4℃ cold storage in this invention;

[0032] Figure 4 Radar chart showing the combined performance of the optimal embodiment and the traditional control sample in this invention. Detailed Implementation

[0033] The following will refer to the appendices in the embodiments of the present invention. Figure 1-4The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] S1. Black Rice Pre-treatment: The raw black rice is screened through a double-layer vibrating screen to remove sand, shriveled grains, and foreign impurities. The upper screen has a mesh size of 5mm and the lower screen has a mesh size of 2mm to remove large-sized impurities and small-sized broken rice and shriveled grains, thereby improving the uniformity of the raw materials. After screening, the rice is quickly washed twice with room temperature running drinking water, with each wash lasting 25 seconds and the water flow speed being 0.5m / s. This causes the rice grains to turn slowly, without kneading the rice grains during the washing process to avoid mechanical damage to the skin.

[0036] After rinsing, drain the surface water using a 30-mesh strainer for 2 minutes, or until no more water droplets fall continuously, then proceed to the next process. This step removes surface dust and free impurities while maximizing the retention of functional components in the skin, thus addressing the issues of nutrient loss and increased glycemic index (GI) caused by over-rinsing.

[0037] S2. Enzymatic softening of the outer layer: Prepare 35℃ constant temperature water at a ratio of 1:1.2 between the dry weight of black rice and the mass of warm water. Add cellulase to the warm water at a rate of 0.02% of the dry weight of black rice and add hemicellulase at a rate of 0.01% of the dry weight of black rice. Stir until the enzyme preparation is completely dissolved, then add the drained black rice. Maintain the system temperature at 35℃ and soak for 4 hours. During the soaking period, stir lightly every 30 minutes at a speed of 20 r / min. The stirring intensity should be such that it does not cause mechanical damage to the rice grains, promote the uniform flow of the enzyme solution, and ensure that the outer layer of all rice grains is uniformly hydrolyzed.

[0038] This step softens the skin through the aforementioned enzymatic hydrolysis reaction, thus addressing the issues of a hard core and rough texture caused by the dense skin during conventional cooking.

[0039] S3. Calcium Salt Cross-linking and Shaping: After enzyme soaking, calcium lactate is added to the soaking system at a rate of 0.08% of the total mass of the soaking solution, and calcium gluconate is added at a rate of 0.04% of the total mass of the soaking solution. After stirring until the calcium salts are completely dissolved, the system temperature is maintained at 35°C and left to stand for 30 minutes. During the standing period, no vigorous stirring is performed to avoid damaging the cross-linking structure that is forming on the surface of the rice grains. This allows calcium ions to fully penetrate into the surface tissue of the rice grains, and the structure is stabilized through the above-mentioned ion bridging reaction, thereby strengthening the structural stability of the rice grains and solving the problems of rice grain cracking and mushy soup during subsequent high-temperature cooking.

[0040] S4. High-pressure synergistic gelatinization: After the black rice has been shaped by calcium salt, drain it and add drinking water at a ratio of 1:1.1 (dry weight of black rice to drinking water). Add baking soda at 0.05% of the dry weight of the black rice, add salt at 0.1% of the dry weight of the black rice, and add first-grade soybean salad oil at 0.3% of the dry weight of the black rice.

[0041] Separately, take 1% trehalose and 0.5% soluble soybean polysaccharide by dry weight of black rice, and dissolve them completely in 40℃ drinking water beforehand. Add them to the black rice and stir at a low speed of 30r / min in the same direction for 3 minutes to ensure that the materials are mixed evenly without powder agglomeration or uneven moisture distribution. Place the mixed materials into a commercial high-pressure cooking equipment, pressurize it to the internal gauge pressure of 40kPa (corresponding to a cooking temperature of 110℃), and maintain constant pressure and temperature for 50 minutes. Do not manually release air during the entire cooking process to keep the temperature and pressure inside the pot stable.

[0042] Once the set cooking time is reached, immediately turn off the heating source and keep the equipment sealed for 10 minutes, without releasing pressure or opening the lid. The residual heat and pressure ensure even heat and moisture transfer within the rice grains, guaranteeing uniform gelatinization. This step accelerates moisture penetration and starch gelatinization through a high-pressure environment, while the synergistic effect of weak alkali, oil, and salt improves texture and prevents sticking. The pre-dispersion of anti-retrogradation components lays the foundation for subsequent inhibition of retrogradation, thus addressing the issues of insufficient gelatinization and uneven texture associated with cooking under normal pressure.

[0043] S5. Gradient cooling and packaging: After high-pressure cooking, the pressure inside the equipment is slowly reduced to normal pressure within 12 minutes by natural pressure release to avoid a sudden drop in pressure caused by rapid pressure release and vaporization of moisture inside the rice grains that breaks through the skin. After pressure release, open the lid and spread the black rice evenly on a sterilized and breathable tray with a material layer thickness of 2cm to avoid the surface moisture from drying out due to an excessively thick material layer or an excessively thin material layer.

[0044] After being spread out, the rice is first cooled to 60°C using room temperature air cooling with a 0.22μm filter membrane for sterilization. This reduces excessive softening of starch due to high temperatures and maintains the elasticity of the rice grains. Then, it is transferred to a Class 100 cleanroom cooling chamber at 18°C ​​and 60% relative humidity, where vertical laminar flow clean air further reduces the core temperature to 20°C. The entire cooling process takes 38 minutes, quickly passing through the temperature range where starch easily retrogrades, thus reducing starch rearrangement and crystallization. After cooling, the rice is vacuum-sealed in a Class 100 cleanroom using food-grade high-temperature resistant retort pouches to obtain a highly soft and glutinous all-black rice product. This step, through gradient cooling, reduces starch retrogradation and damage to the rice grain structure, addressing the issues of rapid retrogradation and grain shrinkage and hardening that occur with natural cooling.

[0045] Example 2

[0046] S1. Black rice pretreatment: The same batch of Grade 1 black rice as in Example 1 was used. After removing impurities by screening with a double-layer vibrating screen, it was quickly rinsed once with room temperature running drinking water for 30 seconds at a flow rate of 0.5 m / s. The rice grains were not rubbed during the rinsing process. Then, it was drained with a 30-mesh draining net for 2.5 minutes until no continuous water droplets fell.

[0047] S2. Enzymatic softening of the outer layer: Prepare 40℃ constant temperature water at a ratio of 1:1.5 between the dry weight of black rice and the mass of warm water. Add cellulase to the warm water at a rate of 0.04% of the dry weight of black rice and add hemicellulase at a rate of 0.02% of the dry weight of black rice. Stir until the enzyme preparation is completely dissolved, then add the drained black rice. Maintain the system temperature at 40℃ and soak for 3 hours. During the soaking period, stir gently at a speed of 20 r / min every 30 minutes to ensure uniform enzymatic hydrolysis.

[0048] S3, Calcium Salt Crosslinking and Shaping: After enzyme soaking, add calcium lactate to the soaking system at a rate of 0.12% of the total mass of the soaking solution, and add calcium gluconate at a rate of 0.06% of the total mass of the soaking solution. Stir until the calcium salt is completely dissolved, and then maintain the system temperature at 40℃ and let it stand for 22 minutes to allow calcium ions to fully penetrate and complete the crosslinking and shaping.

[0049] S4. High-Pressure Collaborative Gelatinization: After shaping, drain the black rice and add drinking water at a ratio of 1:1.3 (dry weight of black rice to drinking water). Add baking soda (0.1% of dry weight of black rice), salt (0.2% of dry weight of black rice), and first-grade soybean salad oil (0.5% of dry weight of black rice). Separately, take 2% trehalose and 1% soluble soybean polysaccharide by dry weight of black rice, and dissolve them completely in 45℃ drinking water beforehand. Add this to the black rice mixture and stir at a low speed of 45r / min in the same direction for 2.5 minutes to ensure uniform mixing. Place the mixture into a high-pressure cooking device, pressurize it to 50kPa, and maintain constant pressure and temperature for 40 minutes. Do not manually release air during the entire cooking process. After reaching the set time, turn off the heating source and simmer in a sealed container for 7 minutes to ensure uniform gelatinization of the rice grains.

[0050] S5. Gradient Cooling and Packaging: After high-pressure cooking, the pressure is naturally released for 10 minutes to atmospheric pressure. The black rice is spread evenly on a sterile, breathable tray with a layer thickness of 2.5 cm. First, the center temperature of the rice is reduced to 65°C using sterile room temperature air cooling. Then, it is transferred to a Class 100 cleanroom cooling room at 20°C and 65% relative humidity. The center temperature is reduced to 22°C using vertical laminar flow air. The entire cooling process takes 30 minutes. After cooling, the rice is vacuum-sealed and packaged in a Class 100 cleanroom environment to obtain the finished product.

[0051] Example 3

[0052] S1. Black Rice Pretreatment: Using Grade 1 black rice from the same batch as in Example 1, the rice was screened to remove impurities using a double-layer vibrating sieve. It was then quickly rinsed once with room-temperature running drinking water for 20 seconds at a flow rate of 0.5 m / s. The rice grains were not rubbed during rinsing. Afterward, the rice was drained through a 30-mesh strainer for 3 minutes until no continuous water droplets fell. S2. Enzymatic Softening of the Outer Layer: A constant temperature of 45°C was prepared using a black rice dry weight to warm water ratio of 1:1.8. Cellulase was added to the warm water at a rate of 0.06% of the black rice dry weight, and hemicellulase was added at a rate of 0.03% of the black rice dry weight. The mixture was stirred until the enzyme preparations were completely dissolved. The drained black rice was then added, and the system was maintained at a constant temperature of 45°C for 2 hours. During soaking, the mixture was gently stirred every 30 minutes at a speed of 20 r / min to ensure uniform enzymatic hydrolysis.

[0053] S3, Calcium Salt Crosslinking and Shaping: After enzyme soaking, add calcium lactate to the soaking system at a rate of 0.15% of the total mass of the soaking solution, and add calcium gluconate at a rate of 0.08% of the total mass of the soaking solution. Stir until the calcium salt is completely dissolved, and then maintain the system temperature at 45℃ and let it stand for 15 minutes to allow calcium ions to fully penetrate and complete the crosslinking and shaping.

[0054] S4. High-Pressure Collaborative Gelatinization: Drain the shaped black rice and add drinking water at a ratio of 1:1.5 (dry weight of black rice to drinking water). Add baking soda (0.15% of dry weight of black rice), salt (0.3% of dry weight of black rice), and first-grade soybean salad oil (0.8% of dry weight of black rice). Separately, dissolve 3% trehalose and 1.5% soluble soybean polysaccharide (3% of dry weight of black rice) in 50℃ drinking water until completely dissolved. Add this to the black rice mixture and stir at 60 rpm in the same direction for 2 minutes to ensure even mixing. Place the mixture in a high-pressure cooking device and pressurize it to 60 kPa. Maintain constant pressure and temperature for 30 minutes without manual venting. After the set time is reached, turn off the heating source and simmer in a sealed container for 5 minutes to ensure uniform gelatinization of the rice grains.

[0055] S5. Gradient Cooling and Packaging: After high-pressure cooking, the pressure is naturally released for 8 minutes to atmospheric pressure. The black rice is spread evenly on a sterile and breathable tray with a material layer thickness of 3cm. First, the center temperature of the rice is reduced to 70℃ using sterile room temperature air cooling. Then, it is transferred to a Class 100 clean cooling room at 22℃ and 70% relative humidity. The center temperature is reduced to 25℃ using vertical laminar flow air. The entire cooling process takes 25 minutes. After cooling, the rice is vacuum sealed and packaged in a Class 100 clean environment to obtain the finished product.

[0056] Comparative Example

[0057] Grade 1 black rice from the same batch as in the example was used. It was simply rinsed twice, 30 seconds each time, with normal kneading force. After draining, it was not subjected to enzyme soaking for softening or calcium salt shaping treatment. No auxiliary materials such as baking soda, trehalose, soluble soybean polysaccharide, salad oil, or edible salt were added. Drinking water was added only at a ratio of 1:1.2 between the dry weight of the black rice and the mass of drinking water. The rice was placed in a regular household rice cooker. To achieve a similar softness and glutinousness as in the example, it was continuously cooked at 100°C under normal pressure for 70 minutes. After the rice cooker automatically switched to the keep-warm setting, it was simmered for 10 minutes. After being removed, it was allowed to cool naturally to 25°C at room temperature. It was then vacuum-sealed in the same cooking bag as in the example and used as the control group sample.

[0058] Statistical Analysis of Experimental Results

[0059] The samples prepared in the three examples and the comparative example were tested for immediate processing quality, cold storage quality, and reheating quality, and the results are as follows:

[0060] Table 1 Comparison of real-time processing quality between each embodiment and the comparative example.

[0061] Group Degradation rate of coarse fibers in the cortex (%) Rice grain integrity rate (%) Central starch gelatinization degree (%) Solid content of cooking liquid (mg / 100mL) Texture hardness of finished product (g) Anthocyanin retention rate (%) Finished product GI value Example 1 22.3 92.1 93.5 21.4 112 94.2 48 Example 2 28.7 95.6 97.2 12.7 93 96.7 47 Example 3 34.2 91.4 98.1 23.8 87 93.5 48 Comparative Example 2.1 61.8 93.8 116.3 108 63.7 57

[0062] Interpretation of the results in Table 1: The data in this table show that, through the multi-level synergistic effect of enzymatic softening of the outer layer, calcium salt cross-linking and shaping, and high-pressure synergistic gelatinization, the three examples achieved a central starch gelatinization degree of over 93%, which is comparable to the gelatinization degree achieved by the comparative example through long-term normal-pressure cooking. At the same time, the rice grain integrity rate remained above 90%, and the solid content of the cooking liquid was only 11%-20% of that of the comparative example. This indicates that the problems of endosperm overflow, mushy soup, and large-area damage to rice grains were effectively controlled.

[0063] Meanwhile, the anthocyanin retention rate of all three examples exceeded 93%, and the GI value of the finished product remained in the low GI range below 55, achieving both a soft and glutinous texture while preserving the intact grain shape and original nutritional properties of black rice. In contrast, the comparative example required prolonged cooking under normal pressure to achieve a similar degree of starch gelatinization, resulting in a grain breakage rate of nearly 40%. The high solids content of the cooking liquid led to significant thickening and sticking of the broth. Furthermore, the washing, kneading, and prolonged high-temperature heating caused substantial anthocyanin loss, raising the GI value of the finished product to 57 and negating the original low GI properties of black rice.

[0064] To further verify the anti-retrogression and reheat stability of the finished products, all samples were stored at a constant temperature of 4℃, and the relevant quality indicators were tested after 7 days and 14 days of refrigeration. The results are as follows:

[0065] Table 2 Comparison of cold storage and reheating quality of each embodiment and comparative example.

[0066] Group Starch retrogradation rate (%) after refrigeration at 4℃ for 7 days Texture hardness (g) after refrigeration for 7 days and microwave reheating for 3 minutes Rice grain adhesion rate after reheating (%) Starch retrogradation rate (%) after 14 days of refrigeration at 4℃ Texture hardness (g) after refrigeration for 14 days and microwave reheating for 3 minutes Example 1 13.2 121 3.1 17.6 135 Example 2 11.5 102 1.8 14.2 116 Example 3 12.7 97 3.5 16.9 112 Comparative Example 38.7 246 16.4 52.3 312

[0067] Explanation of the results in Table 2: The data in this table show that the three examples, through the anti-retrogradation effect of the combination of trehalose and soluble soybean polysaccharides, combined with the gradient rapid cooling process, significantly reduced the rearrangement crystallization rate of starch during cold storage. The starch retrogradation rate was controlled within 15% after 7 days of cold storage. The hardness after reheating was very close to that of freshly cooked products, and the rice grain adhesion rate was maintained at a low level.

[0068] Even after 14 days of refrigeration, the retrogradation rate was still significantly lower than that of the control group after 7 days of refrigeration. After reheating, there was no obvious hardening or gritty texture. The control group had no anti-retrogradation treatment and the natural cooling process was time-consuming. During refrigeration, the starch retrograded rapidly, and after reheating, the hardness increased significantly, and the starch became severely sticky, making it difficult to meet the requirements for refrigerated distribution.

[0069] This invention achieves a balance between the two through a three-level synergistic mechanism: First, the outer layer is softened by enzymes, and the dense network of coarse fibers in the outer layer is cut off by the targeted degradation of cellulase and hemicellulase, reducing the water penetration resistance. The endosperm starch can be fully gelatinized without excessive heating to achieve a soft and glutinous texture, which corresponds to the limitations of parameters such as enzyme soaking temperature, rice-water ratio, enzyme addition amount, soaking time, and stirring frequency in claim 2.

[0070] Secondly, by using the ionic cross-linking and shaping of compound calcium salts, and taking advantage of the complementary permeation rates of calcium lactate and calcium gluconate, a cross-linking network of appropriate strength is formed in the rice grain cortex and surface endosperm, which improves the structural stability of the rice grain and avoids cortex rupture caused by starch expansion during high-pressure cooking.

[0071] Finally, through temperature and pressure control, rice-to-water ratio adjustment, and synergistic use of auxiliary ingredients during the high-pressure cooking process, uniform starch gelatinization is achieved under a pressure of 40-60 kPa. The addition of oil, salt, and baking soda regulates the gelatinization process, preventing excessive localized gelatinization that could lead to grain breakage. Furthermore, the sealed simmering process after cooking ensures even moisture distribution within the rice grains, further enhancing the uniformity of texture. As shown in Table 1, in all three examples, while achieving a high level of softness and glutinousness with a central gelatinization degree exceeding 93%, the rice grain integrity rate remained above 90%, the cooking liquid had extremely low solids content, and there was no significant thickening of the broth, fundamentally resolving the contradiction between softness and glutinousness and grain integrity.

[0072] This invention inhibits retrogradation from two dimensions: molecular blocking and process control. On the one hand, by combining trehalose and soluble soybean polysaccharides, small molecule trehalose can enter the starch granules and form hydrogen bonds with starch molecules, while large molecule soluble soybean polysaccharides can form a hydrophilic barrier on the surface of gelatinized starch granules, thus blocking the association and rearrangement between starch molecules at the molecular level. Combined with the pre-dissolving addition process, it ensures the uniform distribution of anti-retrogradation components.

[0073] On the other hand, by using a gradient rapid cooling process, first air cooling pre-cooling and then constant temperature cooling, the rice grains can quickly pass through the temperature range where starch is prone to retrogradation while maintaining the integrity of the grain structure, thus reducing the time window for starch rearrangement and crystallization.

[0074] As can be seen from the data in Table 2, the starch retrogradation rate of the three examples after 7 days of refrigeration did not exceed 15%, and the hardness after reheating was not significantly different from that of the fresh product. There were no obvious problems of sticking or hardening, which can meet the needs of ready-to-eat products that require long-term refrigeration and distribution.

[0075] This invention employs a non-grinding enzymatic softening process. The pretreatment stage uses a double-layer vibrating screen to precisely remove impurities, followed by a short-time, rapid, and gentle rinsing with room-temperature running water. This avoids mechanical damage to the skin caused by rubbing. The enzymatic hydrolysis process only degrades the cross-linked structure of the skin fibers without destroying the overall integrity of the skin. Efficient water penetration can be achieved without grinding to remove the skin, maximizing the retention of functional components such as dietary fiber and anthocyanins in the skin.

[0076] As shown in Table 1, the anthocyanin retention rate of all three examples exceeded 93%, dietary fiber was fully preserved, and the GI value of the finished product remained below 55, meeting the requirements for low-GI foods and retaining the original nutritional characteristics of black rice. All finished product indicators of the examples met the requirements of claim 10: the rice grain integrity rate was not less than 90%, and there were no issues with rice clumping or sticky bottoms.

[0077] After being refrigerated at 4℃ for 7 days, the starch retrogradation rate is no higher than 15%, and the anti-aging effect is stable; the glycemic index of the finished product is no higher than 55, which is a low-GI food; after being reheated in a microwave or boiling water bath for 3-5 minutes, it still maintains a soft, glutinous and elastic texture, without obvious retrogradation, hardening, sticking and clumping, which can meet the production and distribution needs of industrialized ready-to-eat black rice.

[0078] Reference Figure 2 This bar chart visually compares the differences in fresh processing quality between the multi-stage synergistic process and the traditional atmospheric pressure cooking process. The traditional process lacks enzymatic hydrolysis of the outer layer and calcium salt shaping treatment, relying solely on prolonged high-temperature cooking to gelatinize starch. The undegraded outer layer fibers lead to poor water permeability, causing rice grains to swell and crack. The cooking liquid has a solids content as high as 116.3 mg / 100 mL, resulting in severe stickiness. Simultaneously, the kneading, washing, and prolonged heating cause significant anthocyanin loss, raising the GI value to 57, exceeding the low GI standard. This invention uses enzymatic hydrolysis to soften the outer layer, improving water permeability; calcium salt cross-linking strengthens the rice grain structure; and high-pressure uniform gelatinization. In all three examples, the rice grain integrity rate was above 90%, the anthocyanin retention rate exceeded 93%, and the GI remained stable in the low GI range of 47-48, balancing a soft and glutinous texture, intact rice grain shape, and nutrient retention.

[0079] Reference Figure 3This figure quantifies the aging differences between the anti-retrogradation system of this invention and traditional methods after refrigeration. Traditional black rice, without the addition of trehalose and soluble soybean polysaccharides as anti-retrogradation additives, only undergoes natural cooling at room temperature. This results in starch molecules rearranging and crystallizing for an extended period within the temperature range prone to retrogradation. After 7 days of refrigeration, the retrogradation rate reaches 38.7%, and after 14 days, it exceeds 50%. Microwave reheating doubles the hardness, and the rice grains become severely sticky, making long-term refrigeration and distribution impossible. This invention, by using trehalose and soluble soybean polysaccharides to block starch association and employing a gradient rapid cooling process to shorten the starch crystallization window, achieves a starch retrogradation rate of less than 15% after 7 days of refrigeration in all three examples. Even after 14 days, the retrogradation rate remains significantly lower than the short-term storage level of the comparative example. Reheating results in minimal increase in hardness, with rice grains dispersed without clumping, meeting the shelf-life requirements for industrially refrigerated ready-to-eat foods.

[0080] Reference Figure 4 This radar chart comprehensively compares the advantages and disadvantages of the optimal process of this invention with traditional cooking methods from six dimensions: finished product appearance, nutrition, glycemic properties, cold chain storage and reheating. Traditional processes suffer from multiple defects, including severe rice grain damage, significant anthocyanin loss, high GI value, easy starch aging, and clumping upon reheating. All indicators score at extremely low levels, failing to meet the demands of industrialized production and health food for ready-to-eat black rice. This invention integrates a complete set of synergistic processes: enzymatic softening of the outer layer, calcium salt cross-linking and shaping, high-pressure uniform gelatinization, anti-retrogradation additive formulation, and gradient rapid cooling. This comprehensively addresses the core shortcomings of traditional products, resulting in rice with intact grain shape, high anthocyanin retention, low GI health properties, excellent cold chain anti-aging capabilities, and a dispersed texture upon reheating. It is suitable for various application scenarios, including supermarket cold chain ready-to-eat staple foods and special sugar-controlled diets.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing highly soft and glutinous all-black rice, belonging to the field of grain deep processing technology, characterized in that... Includes the following steps: S1. Enzymatic softening of the outer layer: Select edible black rice and soak it in warm water with added cellulase and hemicellulase at a constant temperature. The coarse fiber cross-linking structure of the dense outer layer of black rice is degraded by enzymatic hydrolysis, so as to achieve uniform softening of the outer layer of black rice. S2, Calcium Salt Crosslinking and Shaping: Add compound calcium salt to the black rice soaking system after enzyme soaking treatment. The compound calcium salt is composed of calcium lactate and calcium gluconate. Keep warm and stand to allow calcium ions to penetrate into the black rice bran and surface endosperm. S3. High-pressure synergistic gelatinization: After the black rice has been shaped by calcium salt, drain it and add drinking water, baking soda, edible salt and edible salad oil according to the set ratio. At the same time, add compound anti-retrogression components, which are composed of trehalose and soluble soybean polysaccharides. After all materials are mixed evenly, they are placed in a high-pressure environment for cooking. S4. Cooling and Packaging: After the cooked black rice is subjected to gradient rapid cooling, it is sealed and packaged in a sterile and clean environment to obtain a finished product of highly soft and glutinous black rice.

2. The method for making highly soft and glutinous all-black rice according to claim 1, characterized in that, The process parameters for constant temperature soaking in S1 are as follows: The temperature of the soaking water is stably controlled at 35-45℃; the mass ratio of dry weight of black rice to warm water in the soaking system is 1:1.2-1:1.8, and the liquid level is 2-3cm higher than the black rice pile; the cellulase activity is 10000U / g, and the addition amount is 0.02%-0.06% of the dry weight of black rice; the hemicellulase activity is 8000U / g, and the addition amount is 0.01%-0.03% of the dry weight of black rice; the total soaking time at constant temperature is 2-4 hours, and the soaking system is lightly stirred every 30 minutes during the soaking period.

3. The method for making highly soft and glutinous black rice according to claim 1, characterized in that, The amount of compound calcium salt added in S2 is based on the total mass of the soaking solution, with calcium lactate added at 0.08%-0.15% and calcium gluconate added at 0.04%-0.08%. After the calcium salt is added, the soaking system temperature is maintained at 35-45℃ and kept warm for 15-30 minutes.

4. The method for making highly soft and glutinous all-black rice according to claim 1, characterized in that, In step S3, the mass ratio of drained black rice to drinking water is 1:1.1-1:1.5; the amount of baking soda added is 0.05%-0.15% of the dry weight of black rice; the amount of edible salt added is 0.1%-0.3% of the dry weight of black rice; the amount of edible salad oil added is 0.3%-0.8% of the dry weight of black rice; after all ingredients are added, stir slowly in the same direction at a speed of 30-60 r / min for 2-3 minutes.

5. The method for producing highly soft and glutinous all-black rice according to claim 1, characterized in that, The amount of trehalose added in S3 is 1%-3% of the dry weight of black rice, and the amount of soluble soybean polysaccharide added is 0.5%-1.5% of the dry weight of black rice. The combination of the two anti-retrogradation components can inhibit starch retrogradation from different levels. Trehalose is a small molecule disaccharide. Before adding trehalose and soluble soybean polysaccharide, they are stirred with an appropriate amount of drinking water at 40-50℃ until completely dissolved, and then added to the black rice material along with the other ingredients.

6. The method for producing highly soft and glutinous all-black rice according to claim 1, characterized in that, The process parameters for high-pressure cooking in S3 are as follows: the high-pressure cooking equipment uses a commercial pressure cooker with electric heating or steam heating, and the internal pressure is stably controlled at 40-60 kPa, corresponding to a cooking temperature of 110-120℃; after the equipment reaches the set pressure and temperature, it is maintained at constant pressure and temperature for 30-50 minutes. The cooking time is slightly adjusted according to the age of the black rice, and the cooking time is appropriately extended by 5-10 minutes for black rice that has been stored for more than 6 months.

7. The method for producing highly soft and glutinous black rice according to claim 1, characterized in that, The specific steps of gradient rapid cooling in S4 are as follows: After the high-pressure cooking is completed, the pressure inside the equipment is first naturally released to reduce the pressure to normal pressure. The pressure release time is controlled to be 8-12 minutes. The black rice is evenly spread on a sterile and breathable tray with a layer thickness of 2-3 cm. If the layer is too thin, the surface moisture will be lost and the rice will become dry and hard. After spreading the rice out, use room temperature air cooling with a 0.22μm filter membrane to reduce the center temperature of the rice to 60-70℃, thereby reducing the starch from becoming too soft and mushy at high temperatures and maintaining the elasticity of the rice grains. Then transfer it to a sterile cooling room at 18-22℃ and 60%-70% relative humidity, and use vertical laminar flow clean air to reduce the center temperature to 20-25℃; the entire cooling process shall not exceed 40 minutes.

8. The method for producing highly soft and glutinous black rice according to claim 1, characterized in that, Before the S1 enzymatic softening of the outer layer, a black rice pretreatment process is also included: the raw black rice is screened through a double-layer vibrating screen to remove sand, shriveled grains, and foreign impurities. The upper screen has a mesh size of 5mm and the lower screen has a mesh size of 2mm to remove large-diameter impurities and small-diameter broken rice and shriveled grains, thereby improving the uniformity of the raw materials. After screening, rinse quickly 1-2 times with room temperature running drinking water, with each rinse lasting no more than 30 seconds. After rinsing, drain the surface water with a 30-mesh strainer for 2-3 minutes until no obvious water droplets fall, then proceed to the enzyme immersion process.

9. The method for producing highly soft and glutinous all-black rice according to claim 6, characterized in that, After the high-pressure cooking time reaches the set cooking time, immediately turn off the heating source and keep the high-pressure equipment in a sealed state for 5-10 minutes. Do not release pressure or open the lid during the simmering process. During the high-pressure cooking stage, the starch gelatinization degree of the surface layer of the rice grain is slightly higher than that of the internal endosperm. By simmering in a sealed state, the surface moisture can gradually penetrate into the inside, and the internal starch can be further gelatinized under the action of residual heat, ultimately achieving uniform gelatinization degree of the rice grain from the outside to the inside.

10. The method for producing highly soft and glutinous all-black rice according to claim 1, characterized in that, The resulting high-softness, glutinous, all-black rice has a grain integrity rate of no less than 90%; after refrigeration at 4℃ for 7 days, the starch retrogradation rate is no higher than 15%; the glycemic index of the finished product is no higher than 55; and it retains its soft, glutinous, and elastic texture after being reheated in a microwave or boiling water bath for 3-5 minutes.

Images