Method for regulating and controlling water absorption characteristic and cooking quality of rice based on layered grinding

Abstract

The invention provides a method for regulating and controlling water absorption characteristics and cooking quality of rice based on layered grinding, and belongs to the technical field of food processing. The rice is subjected to layered grinding, and the rice with the good water absorption characteristic and cooking quality is obtained; the grinding degree of the layered grinding is 1 to 12 percent, and the time of the layered grinding is 47s to 787s. The invention finds that the 4% milling degree can obviously improve the water absorption rate of the rice, improve / reduce the water absorption dynamic parameter value of the rice, and improve the water state distribution of the rice. And the crack effect of rice with the grinding degree of 2% or above is obviously improved. Layered grinding can shorten the optimal cooking time of rice, and the pH value of rice water, the loss content of rice water solids, the rice elongation rate, the volume expansion rate and the iodine blue value are increased. Grinding 4% is an obvious change critical point of the eating quality of the rice, and grinding 6% is an obvious change critical point of the appearance color of the rice. By controlling the grinding degree within 4% or 6% and controlling the soaking time and the like, the rice with good water absorption characteristic and cooking quality can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, and in particular relates to a method for controlling the water absorption characteristics and cooking quality of rice based on layered milling. Background Technology

[0002] Excessive milling will cause the loss of nutrients, but soaking inevitably brings the surface dust and microorganisms of brown rice into the soaking solution. At the same time, soaking will breed various bacteria, molds and other harmful microorganisms, and at the same time, it will make the rice structure loose and porous, causing nutrients such as protein, starch and fat to dissolve.

[0003] In recent years, domestic and international research has mainly focused on the effect of soaking temperature on the water absorption characteristics of rice. However, there is little research on how the milling and soaking processes affect the water absorption characteristics and moisture distribution of rice. It is necessary to explore more theoretical studies on the structural effects of water on rice with different milling degrees, including moisture state and rice moisture migration pathways.

[0004] To improve the rough texture of brown rice, biological, physical, and chemical modification methods are used to enhance its cooked and edible quality. However, excessive milling leads to significant nutrient loss. In recent years, the relationship between milling degree and the cooked and edible quality of rice has been a focus of attention. However, existing research mostly concentrates on the effects of single varieties or single milling degrees, lacking a comprehensive analysis of data on the cooked and edible quality and structure of rice with different milling and soaking degrees. These characteristics are equally crucial for improving cooked rice quality. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for controlling the water absorption characteristics and cooking quality of rice based on layered milling, so as to solve the problems of severe loss of rice nutrients and poor eating quality.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for controlling the water absorption characteristics and cooking quality of rice based on layered milling includes the following steps: Brown rice is milled in layers to obtain rice with good water absorption and cooking quality. The grinding degree of the layered grinding is 1~12%, and the grinding time is 47s~787s.

[0007] Preferably, the soaking after the layered grinding is carried out for 0.25 to 8 hours.

[0008] Preferably, the rice includes japonica rice and indica rice, the japonica rice varieties include Henan Xinfeng No. 2 and Huangjinqing, and the indica rice varieties include Anhui Jinyou.

[0009] Preferably, the cooking quality includes optimal cooking time, rice water pH value, rice water solids loss, rice elongation rate, rice expansion rate, and rice iodine blue value.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This invention found that the water absorption rate of all samples showed a trend of first increasing sharply and then stabilizing, and that 4% milling degree could significantly improve the water absorption rate of rice.

[0011] This invention reveals a negative correlation between milling degree and water absorption rate constants K1 and K2, with little difference in K1 and K2 values ​​for rice with milling degrees of 4% or higher. A 4% milling degree can significantly increase / decrease the water absorption kinetic parameters of rice. The water absorption resistance of rice exhibits the following order: outer bran layer > inner bran layer > endosperm layer.

[0012] This invention reveals that the peak intensity of rice gradually increases with prolonged soaking time. Soaking causes the rice to absorb strongly bound water (A). 21 The proportion decreased, and the weakly bound water A 22 and free water A 23 The proportions increased to varying degrees. Anhui Jinyou rice showed the most significant change, with a 4% milling degree noticeably improving the moisture distribution of the rice.

[0013] This invention reveals that moisture gradually diffuses and penetrates into the endosperm layer from the ventral side of the rice and the germ attachment point, almost completely opening the moisture migration channels in rice with a milling degree of 2% or higher. Unsoaked rice has a dense cross-sectional structure, while soaked rice exhibits deep and wide cracks in its cross-section, with a significant improvement in crack formation in rice with a milling degree of 2% or higher.

[0014] This invention discovers that layered milling shortens the optimal cooking time for rice, while increasing the pH of the rice water, the loss of solids in the rice water, the elongation rate of cooked rice, the volume expansion rate, and the iodine blue value. Milling to 4% is the critical point for a significant change in the edible quality of cooked rice, and milling to 6% is the critical point for a significant change in the appearance and color of cooked rice. By controlling the milling degree to within 4% or 6%, and by controlling the soaking time, rice with good water absorption characteristics and cooking quality can be obtained. Attached Figure Description

[0015] Figure 1 The effect of soaking time on the water absorption rate of rice with different milling degrees is shown in the figure (where A is Henan Xinfeng No. 2, B is Huangjinqing, C is Anhui Jinyou, and D is the overall water absorption rate curve). Figure 2 The following is a diagram showing the fitting effect of the Peleg model on the water absorption data and water absorption resistance of rice of different varieties and milling degrees ((a) is Henan Xinfeng No. 2, (b) is Huangjinqing, (c) is Anhui Jinyou, and (d) is the overall water absorption resistance graph). Figure 3The Peleg model fits Mr, Ar(h), and R(h) of different varieties and milling degrees of rice (A is the relative moisture content of Henan Xinfeng No. 2, B is the water absorption rate of Henan Xinfeng No. 2, C is the water absorption resistance of Henan Xinfeng No. 2, D is the relative moisture content of Huangjinqing, E is the water absorption rate of Huangjinqing, F is the water absorption resistance of Huangjinqing, G is the relative moisture content of Anhui Jinyou, H is the water absorption rate of Anhui Jinyou, and I is the water absorption resistance of Anhui Jinyou). Figure 4 The Peleg model is used to fit the dimensionless value of R(d) of rice of different varieties and milling degrees (where A is Henan Xinfeng No. 2, B is Huangjinqing, and C is Anhui Jinyou). Figure 5 The distribution of the A21, A22 and A23 moisture states of MD0~MD6 of Henan Xinfeng No. 2 rice with different milling degrees at different soaking times (0-8 h); Figure 6 The distribution of the A21, A22 and A23 moisture states of Henan Xinfeng No. 2 rice with different milling degrees (MD8~MD12) at different soaking times (0-8 h); Figure 7 The distribution of the A21, A22 and A23 moisture states of MD0~MD6 rice with different milling degrees of Golden Sunny rice at different soaking times (0-8 h); Figure 8 The distribution of the A21, A22 and A23 moisture states of MD8~MD12 rice with different milling degrees of Golden Sunny rice at different soaking times (0-8 h); Figure 9 The distribution of the A21, A22 and A23 moisture states of Anhui Jinyou rice with different milling degrees MD0~MD6 at different soaking times (0-8 h); Figure 10 The distribution of the A21, A22 and A23 moisture states of Anhui Jinyou rice MD8~MD12 with different milling degrees at different soaking times (0-8 h); Figure 11 These are nuclear magnetic resonance (NMR) images showing the effect of soaking on rice with different milling degrees; Figure 12 Soaking time for MD0, MD1, MD2, MD 12 (From top to bottom) The effect of rice cross-section microstructure (×1000) (Note: From left to right, they represent cross-sections of rice soaked for 0, 20, 40, 60, 80, and 120 min, respectively). Figure 13These are actual photos of rice of different varieties and milling levels (A is Henan Xinfeng No. 2, B is Huangjinqing, C is Anhui Jinyou; Note: from left to right and top to bottom, they are MD0, MD1, MD2, MD3, MD4, MD6, MD8, MD...). 10 MD 12 ); Figure 14 The cooking characteristics of rice of different varieties and milling degrees are as follows: (a) Optimal cooking time, (b) Rice elongation rate, (c) pH value of rice water, (d) Loss of solids in rice water, (e) Iodine blue value, and (f) Heating volume expansion rate. Detailed Implementation

[0016] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0017] Henan Xinfeng No. 2 (japonica rice) and Huangjinqing (japonica rice) were purchased from Henan Diyi Technology Development Co., Ltd. (September 2022, Henan), and Anhui Jinyou (indica rice) was purchased from Henan Diyi Technology Development Co., Ltd. (September 2022, Hunan).

[0018] Aspartic acid was purchased from Beijing Siencell Biotechnology Co., Ltd. (through a third-party agent); petroleum ether, anhydrous ethanol, glacial acetic acid, 95% ethanol, and sodium hydroxide were purchased from Tianjin Damao Chemical Reagent Factory; hydrochloric acid was purchased from Sinopharm Chemical Reagent Co., Ltd.; total starch assay kit and amylose assay kit were purchased from Megazyme, Ireland; and dimethyl sulfoxide was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; all experimental reagents (unless otherwise specified) were of analytical grade, and the experimental water was distilled water (the same applies to other reagents).

[0019] The following equipment was purchased: Kumisino rice milling machine (from Quzhou Kumisino Grain Machinery Manufacturing Co., Ltd.), FQS-130X20 rice broken rice screener (from Beijing Shengkun Haili Technology Development Co., Ltd.), SHJ-6ABS magnetic stirring water bath (from Changzhou Jintan Liangyou Instrument Co., Ltd.), S220 pH meter (from Mettler Toledo Instruments (Shanghai) Co., Ltd.), electric thermostatic water bath (from Beijing Yongguangming Medical Instrument Co., Ltd.), L580 Lu Xiangyi centrifuge (from Shanghai Lu Xiangyi Centrifuge Instrument Co., Ltd.), KQ-500VDE three-frequency CNC ultrasonic cleaner (from Kunshan Ultrasonic Instrument Co., Ltd.), FW 80 and FW 100 high-speed universal pulverizers (from Tianjin Test Instrument Co., Ltd.), rapid N cube nitrogen analyzer (from Ailimonta Trading (Shanghai) Co., Ltd.), DGG-9140BD electric thermostatic drying oven (from Shanghai Senxin Experimental Instrument Co., Ltd.), and PL 3002-IC. The electronic analytical balance was purchased from Mettler Toledo Instruments (Shanghai) Co., Ltd., the PYRAMID TX muffle furnace from Beijing Pilmett Technology Co., Ltd., the DL-1 universal electric furnace from Beijing Yongguangming Medical Instrument Co., Ltd., the S-3000N scanning electron microscope from Hitachi, Japan, and the NMI20-030H-I low-field nuclear magnetic resonance imaging system from Suzhou Newmai Analytical Instruments Co., Ltd.

[0020] Example 1

[0021] 1. Preparation of rice samples with different milling degrees

[0022] Brown rice was milled in a Cumexo mill for layered milling. After each test, the equipment was cleaned to avoid cross-contamination of bran powder. All materials were thoroughly cleaned, and data were recorded. Samples were aliquoted and stored at 4°C for later use. Since layered milling could not be precisely controlled to 1%, but the milling error was kept within the ideal range, samples milled to approximately 0%, 1%, 2%, 3%, 4%, 6%, 8%, 10%, and 12% were labeled as: MD0 (brown rice), MD1, MD2, MD3, MD4, MD6, MD8, and MD... 10 MD 12 (White rice).

[0023] Precise grinding was performed using the following parameters (grind belt: 120, grinding current: 2.00-2.65 A, rotation speed: 50 Hz, production capacity: 4000 kg / h, and duration: approximately 50 seconds per cycle). The degree of grinding was calculated as the percentage of the bran layer mass to the brown rice mass, using the following formula: Grinding degree (%) = m1 / m2 × 100% Note: m1 is the mass of rice after milling, and m2 is the mass of brown rice before milling.

[0024] 2. The effect of soaking on the water absorption rate of layered milled rice

[0025] Determination of water absorption rate of rice

[0026] Accurately weigh 5.0 g of rice sample (denoted as m7) and place it in a 50 mL centrifuge tube. Add 30 mL of deionized water and soak for 0, 0.25, 0.5, 0.75, 1, 2, 3, 4, and 5 hours. After soaking, remove the rice sample, blot off the surface moisture with a colander and absorbent paper, and weigh it (denoted as m8). The calculation formula is as follows: Water absorption rate (%) = (m8 - m7) / m7 × 100% The experimental results were measured three times. SPSS 25.0 and Microsoft Excel 2021 were used for data statistics and analysis, and one-way ANOVA, Tukey test and correlation analysis were performed. Origin 2022 software was used for graphing.

[0027] Experimental results: such as Figure 1 As shown. The water absorption curves of all samples showed a trend of first increasing sharply and then stabilizing. The water absorption rate of rice with a milling degree of 4% and above changed significantly in the first 60 minutes of soaking. This may be related to the effective removal of the dense bran layer during the layered milling process, the exposure of the endosperm layer inside the rice, the opening of water migration channels, and the easier penetration of water. This is unrelated to the variety. The final water absorption rates of Henan Xinfeng No. 2, Huangjinqing, and Anhui Jinyou brown rice were 26.45%, 28.53%, and 25.25%, respectively. The final water absorption rates of the three white rice varieties were 30.69%, 32.17%, and 30.89%, respectively. The final water absorption rates of the three white rice varieties were 16.03%, 12.69%, and 22.34% higher than those of brown rice, respectively. The soaking water absorption rate of Huangjinqing MD0 was 9.79% at 20 minutes and gradually increased to 26.06% (120 minutes). Huangjinqing MD2-MD 12 The water absorption rate of the first rice variety was 15.08%-27.89% after 20 min, and then increased to 29.23%-33.54% (120 min). The experimental results for the other two rice varieties were consistent with the above. Layered milling loosened the internal structure of the rice and fully opened the water migration channels. Different varieties of rice had different water absorption capacities, specifically: Huangjinqing > Henan Xinfeng No. 2 > Anhui Jinyou.

[0028] It is worth noting that the water absorption rate of Anhui Jinyou rice did not change significantly with milling degree in the first 2 hours. This may be related to the high broken rice rate during the milling process of indica rice, resulting in a small difference in water absorption capacity during soaking. Light milling can significantly improve the soaking water absorption rate. The water absorption and swelling of rice is a limited and reversible process. Water molecules enter starch granules and combine with free hydrophilic groups. Amylopectin has a highly branched structure and can easily combine with water molecules, but the water absorption capacity of rice is limited. After the rice bran layer and germ are removed, water can quickly penetrate through the damaged areas and diffuse into the endosperm. At this time, the diffusion rate of water in the endosperm affects the soaking water absorption rate, and the degree of milling determines whether water can quickly penetrate through the gaps in the damaged bran layer into the endosperm.

[0029] In summary, there is a clear positive correlation between the degree of milling and the soaking water absorption rate. The rice bran layer creates a significant barrier to water absorption, indicating that the water penetration rate in the rice bran layer is lower than that in the endosperm, which is unrelated to the rice variety.

[0030] 3. Fitting of rice water absorption rate curve

[0031] 3.1 Effect of Layered Milling on Rice Water Absorption Kinetic Parameters

[0032] Construction of the Peleg model for hydration dynamics

[0033] Li et al. (Li XF, Song HY, Chen SH. Impact of pressure and temperature on the hydration resistance of rice[J]. LWT-Food Science and Technology, 2024, 209: 116759) used the Peleg water absorption model to fit the hydration kinetics curve of rice water absorption, including the equilibrium moisture content, hydration rate, and diffusion resistance through the inner and outer bran layers as a function of soaking time. The Peleg model can be expressed by the following formula: Mt-M0=t / (K1+K2 t) K1 and K2 are relevant parameters of the Peleg model, and t represents time (h). By substituting the data from the water absorption curve into formula (1) and plotting the reciprocal of (Mt-M0) against 1 / t, the equilibrium moisture content (Me) is expressed by the following equation when (t→+∞): Me = M0 + 1 / K2 Mr represents the relative moisture content (%), Mt represents the real-time moisture content of the rice (%), M0 represents the initial moisture content (%), and Me represents the equilibrium moisture content (%). The formula is expressed as: Mr = (Mt - M0) / (Me - M0) = K2 t / (K1+K2 t) Taking the first derivative of Mr, the formula for the relative water absorption rate is: Ar = dMr / dt, which can be expressed as: Ar=(2 K2 K2 t+K1 K2) / (K1+K2 t) 2

[0034] The time required for the relative moisture content (Mr) to reach half of its equilibrium value (Mt) is: t 1 / 2 =K1 / K2 Related absorption rate Ar ,1 / 2 for: Ar ,1 / 2 =K2 / (4 K1) = 0.25 t 1 / 2

[0035] Based on the principle of mass transfer, the absorption rate is proportional to the difference between the equilibrium moisture content (Me) and the real-time moisture content (Mt), representing the magnitude of the water absorption resistance. The proportionality factor is the reciprocal of the absorption resistance (R). The water absorption resistance of rice can be expressed as: R = K1 / K2 + t Both the size-based water absorption resistance (Me-Mt) / At and the dimensionless water absorption resistance (1 - Mr) / Ar show the same results. The layer resistance of the outer bran layer of brown rice, the inner bran layer of lightly milled rice, and the endosperm layer of white rice can be determined by the following equation: R(d)=(1-Mr) / Ar=(K1 K1+K1 K2 t) / (2 t K2 K2+K1 K2) R （外糠层） = (K1 / K2) MD0 -(K1 / K2) MD6 R （内糠层） = (K1 / K2) MD6 -(K1 / K2) MD8 R （胚乳层） = (K1 / K2) MD10-(K1 / K2) MD12 The experimental results were measured three times. SPSS 25.0 and Microsoft Excel 2021 were used for data statistics and analysis, and one-way ANOVA, Tukey test and correlation analysis were performed. Origin 2022 software was used for graphing.

[0036] Experimental results: as shown in Table 1 and Figure 2 As shown.

[0037] Table 1. Water absorption kinetic parameters of Peleg model for different rice varieties and milling degrees

[0038] Table 1 shows that the water absorption rate constant K1 of rice gradually decreases with increasing milling degree. A smaller K1 value indicates a faster water absorption rate, and its reciprocal 1 / K1 represents the magnitude of the water absorption rate. The K1 values ​​for Henan Xinfeng No. 2, Huangjinqing, and Anhui Jinyou range from 0.0114 to 0.0056, 0.0129 to 0.0039, and 0.0148 to 0.0055, respectively. (Huangjinqing MD) 12 The K1 value (0.0039) of the rice was lower than that of Henan Xinfeng No. 2 and Anhui Jinyou (0.0056 and 0.0055, respectively). K2, as a capacity constant, indicates that a smaller K2 value represents a stronger water-holding capacity of the rice. With increasing milling degree, the K2 value showed a decreasing trend, indicating that white rice has a stronger water-holding capacity. 1 / K2 represents the predicted final water absorption of the rice sample. The results show that the milling degree during soaking has a significant impact on the water absorption rate of rice. Increased milling degree leads to a gradual decrease in the rice's resistance to water absorption, while excessive milling completely exposes the rice's water migration channels, significantly increasing the water absorption rate. The main barriers causing water absorption resistance during brown rice soaking are the inner and outer bran layers, the secondary resistance factor is the endosperm layer, and other factors mainly include the size of the cracks in the germ of different rice varieties and the uneven distribution of water migration channels.

[0039] The results showed that the K1 values ​​of rice milled to 4% or higher differed little. The outer bran layer of brown rice exhibited a greater resistance to water absorption than the inner bran layer and endosperm layer, further supporting the conclusion that the main factor influencing the water absorption rate of rice is its multi-layered and unevenly distributed structure. When brown rice was milled to 4%, Ar and t... 1 / 2 The values ​​are significantly lower than those of brown rice in terms of kinetic parameters. 1 / 2(Related absorption rate) increases with increasing milling degree, while the water absorption resistance after soaking for 2 hours decreases with increasing milling degree. This indicates that the inner and outer bran layers hinder the rate of water diffusion in rice. Rice with only the endosperm layer is more likely to absorb a large amount of water and reach saturation in a short time. Brown rice and rice with low milling degree absorb water more slowly in a short time than white rice.

[0040] In summary, the variation patterns of water absorption kinetic parameters demonstrate that rice is a multi-layered system with extremely uneven nutrient distribution, and that the hydration kinetic parameters differ among different varieties and milling degrees of rice.

[0041] Depend on Figure 2 It can be seen that the soaking time of rice increases with t / (M) t- The numerical variation of M0) all showed an upward trend. Under the same soaking time, as the grinding degree increased, the fitted t / (M) value increased. t- The M0 values ​​all shifted downwards. Linear fitting of the Peleg model showed that the water-holding constants for the three M0 values ​​were 0.0370, 0.0353, and 0.0357, respectively. 12 The values ​​were 0.0314, 0.0276, and 0.0314, respectively, representing decreases of 15.14%, 21.81%, and 12.04%. The MD6 values ​​were 0.0341, 0.0279, and 0.0325, respectively, compared to MD... 12 Compared to the previous stage, the decrease rates were 7.92%, 1.08%, and 3.38%, respectively, which were much lower. This confirms that the hydration rate growth trend during soaking is closely related to the degree of milling. Rice with a milling degree of 4% or higher has almost no significant difference in water holding capacity compared to white rice, providing a new perspective on the water absorption properties of stratified milled rice.

[0042] The water absorption resistance (outer bran layer, inner bran layer, endosperm layer) of Henan Xinfeng No. 2, Huangjinqing, and Anhui Jinyou rice varieties were 0.0774, 0.0246, 0.0054 and 0.1513, 0.0448, 0.0296 and 0.1960, 0.0321, 0.0239, respectively. The decrease in resistance (R) of the outer and inner bran layers of the three different varieties of brown rice was 68.22%, 70.39%, and 83.62%, respectively, while the decrease in the outer bran layer and endosperm layer was 93.02%, 80.43%, and 87.81%, respectively. This indicates that as the milling degree increases, the R value shows a change pattern of first decreasing sharply and then decreasing slowly. The water absorption resistance of the outer bran layer is much greater than that of the inner bran layer, and the outer bran layer of Anhui Jinyou has the strongest water absorption resistance, followed by Huangjinqing, while Henan Xinfeng No. 2 has the weakest. This may be due to the differences in the bran structure of different varieties of brown rice.

[0043] In summary, the water absorption resistance of the outer bran layer, inner bran layer, and endosperm layer of the three types of rice decreases sequentially, indicating that the main factor affecting the water absorption resistance of rice is concentrated in the outer bran layer, rather than the inner bran layer and endosperm layer. Using mathematical model fitting to explore the magnitude of water absorption resistance in brown rice layers is highly innovative, providing a new perspective on the changing patterns of rice water absorption properties.

[0044] 3.2 Effects of soaking on the relative moisture content, water absorption resistance, and water absorption rate of rice with different milling degrees

[0045] Experimental results: such as Figure 3 , Figure 4 As shown in Table 2.

[0046] Depend on Figure 3 It can be seen that, compared with white rice, the relative moisture content curves and water absorption rate curves of the three different varieties of brown rice shifted downwards, while the water absorption resistance curve shifted upwards, indicating a significant difference in the moisture absorption curves between brown rice and white rice. The relative moisture content curves of all three rice varieties showed a sharp increase followed by a flattening. At the same soaking time, Mr increased with increasing milling degree. After soaking for 60 minutes, the Mr values ​​for Henan Xinfeng No. 2, Huangjinqing, and Anhui Jinyou brown rice were 0.7649, 0.7326, and 0.7063, respectively, while the Mr values ​​for white rice were 0.8486, 0.8759, and 0.8500, respectively. The MD0 value was significantly higher than the MD0 value. 12 The Mr values ​​of brown rice increased by 10.94%, 19.56%, and 20.34%, respectively; the Ar values ​​of the water absorption rates of the three brown rice types were 1.3500, 1.2694, and 1.2053, respectively, while those of white rice were 1.5688, 1.6431, and 1.5725, respectively. The water absorption resistance (R, h) of the three brown rice types increased by 16.20%, 29.43%, and 30.46%, respectively; the R, h values ​​of the three brown rice types were 1.3072, 1.3648, and 1.4156, respectively, while those of white rice were 1.1783, 1.1416, and 1.1764, respectively, representing decreases of 9.86%, 16.35%, and 16.89%, respectively. The Ar values ​​of the three brown rice types were significantly lower than those of white rice. With increasing relative moisture content over time, the absorption rate slowed down, and the fitted value of the water absorption resistance R increased, corroborating the experimental results of rapid short-term water absorption by rice. The kinetic curves also showed divergence or convergence. Brown rice bran is high in fat and dietary fiber, and it adheres firmly to the surface of the endosperm, giving it significant resistance to water penetration.

[0047] Depend on Figure 3As can be seen from C, F and I, the R value of rice with different milling degrees is almost the same when soaked for 2 hours or more. The long soaking time effectively overcomes the resistance of the bran layer, and water penetrates through the bran layer to reach the cracks in the endosperm and diffuses completely into the endosperm. Taking Henan Xinfeng No. 2 rice as an example, the relative moisture content Mr after soaking for 2 hours were 0.8668, 0.8973, 0.9081, 0.8968, 0.9105, 0.9158 and 0.9181, respectively; the absorption rate Ar was 0.8090, 0.8512, 0.8664, 0.8978, 0.8127, 0.8773 and 0.8805, respectively; and the water absorption resistance R was 2.3073, 2.2289, 2.2022, 2.2299, 2.2053, 2.1837 and 2.1783, respectively. The results of the other two types of rice were consistent with the above experimental results.

[0048] The results showed that all samples overcame water absorption resistance and rapidly absorbed water within a short soaking period, after which the absorption rate slowed down until saturation was reached, consistent with the experimental results of rice water absorption rate curves. The water absorption resistance of the three rice varieties showed a consistent change pattern after 1 hour, demonstrating that rice grains hardly absorbed any more water after prolonged soaking. Regardless of soaking time and milling degree, the resistance converged over time, with significant differences observed during short-term soaking. Brown rice and lightly milled rice exhibited significantly higher short-term soaking water absorption resistance than white rice. This difference is attributed to the resistance between the outer and inner bran layers; brown rice has a narrower resistance range because water has difficulty penetrating the capillary fissures in the outer bran layer, while the endosperm layer of white rice facilitates water entry into these fissures.

[0049] In summary, the Peleg model can effectively predict the differences in water absorption behavior of rice with different milling degrees under the same soaking time, providing a theoretical basis for optimizing rice soaking processes and offering a scientific theory for exploring water migration pathways during rice soaking.

[0050] Depend on Figure 4 It can be seen that, under the same soaking time conditions, the dimensionless water absorption resistance (R,d) of all samples showed a decreasing trend, indicating that the water absorption capacity of rice increases with the degree of milling. Water absorption resistance (R,d) reflects the ease with which water penetrates the rice grains. The water absorption resistance (R,d) values ​​of the three types of brown rice decreased more rapidly, while those of the three types of white rice decreased more slowly. This may be because the surface of rice with a higher degree of milling is rougher and has higher porosity, thus providing more channels for water penetration without needing to overcome additional water absorption resistance; the results for brown rice are the opposite. Furthermore, the milling process disrupts the cell wall structure of rice, fully exposing starch granules and increasing the soaking water absorption rate, which is consistent with the experimental results regarding water absorption rate mentioned above.

[0051] Table 2 Correlation analysis of water absorption kinetic parameters of Peleg model rice with different milling degrees

[0052] Table 2 shows that K1 and K2 are significantly negatively correlated with the degree of milling, indicating that layered milling enhances the water absorption rate and water holding capacity of rice. This is because layered milling disrupts the surface structure of the rice grains, exposing the endosperm layer. K2 and K1 show a significant positive correlation, indicating that their parameter changes follow the same pattern, suggesting that rice samples with faster water absorption rates generally also have higher water holding capacities. Me shows a significant negative correlation with K1 and K2, indicating that white rice has a higher moisture content when water absorption reaches equilibrium. The degree of milling is significantly negatively correlated with water absorption resistance (R), possibly because white rice needs to overcome less resistance during water absorption, while brown rice shows the opposite, exhibiting a continuous water absorption and expansion pattern, consistent with the water absorption rate curve of layered milled rice. These results provide data support for understanding the rice soaking and water absorption process.

[0053] 4. The effect of soaking on the moisture state of rice during layered milling

[0054] Rice samples were soaked at a rice-to-water ratio of 1:2 (m / m) for 0 min, 20 min, 40 min, 60 min, 80 min, 2 h, 4 h, 6 h, and 8 h, and then drained. To avoid moisture evaporation, the sample was quantified (approximately 3 g) and quickly placed in a transparent glass bottle, sealed, and equilibrated at 25 °C. The NMR analysis parameters were: number of sampling points (TD) 74996, number of iterations (NS) 32, main frequency (SF) 21.0 MHz, sampling frequency (SW) 100 kHz, and temperature 25 °C. Inversion parameters: number of data points 300, number of iterations 1,000,000.

[0055] The experimental results were measured three times. SPSS 25.0 and Microsoft Excel 2021 were used for data statistics and analysis, and one-way ANOVA, Tukey test and correlation analysis were performed. Origin 2022 software was used for graphing.

[0056] Experimental results: such as Figures 5-10 As shown, the distribution and proportion of moisture inside the rice change significantly with prolonged soaking time. 21 The increase in peak relaxation time indicates that the migration rate of water within the rice is accelerated, the water binding state changes, and the water migration channels in the rice are opened, making it easier for water to diffuse within the rice. 22 T 23The decrease in relaxation time reflects a weakening of the binding force between moisture and the internal components of rice, which may lead to A 21 Transform into A 22 Or A 23 The increase in peak intensity further confirms the effect of soaking on the internal moisture state and content of rice. Anhui Jinyou brown rice, after soaking at room temperature for 8 hours, showed... 23 A 22 and A 21 The proportions were 4.7%, 13.3%, and 82.0%, respectively, compared to MD 12 The percentages of increase / decrease in rice were 12.3%, 9.6%, and 78.1%, respectively, with increases / decreases of 161.70%, 27.82%, and 4.99%, showing a consistent trend across almost all samples. Meanwhile, unsoaked rice A... 21 The high content ratio indicates that T 21 Rigid protons have a higher density, and water and non-aqueous components are tightly bound together, resulting in a higher proportion of strongly bound water. The higher the degree of milling of the rice, the higher the proportion of A under long-term soaking conditions. 23 and A 22 The higher the total proportion, the higher the proportion of A in the white rice during soaking. 22 and A 23 This indicates that the system contains a higher proportion of free water. This is unrelated to the variety.

[0057] In summary, the A of the three types of white rice 22 and A 23 The relative content is generally higher in brown rice than in brown rice, indicating that the surface structure of brown rice is denser. The presence of the bran layer creates significant resistance to water absorption, meaning that water can only be partially adsorbed onto the surface of the grain, leading to a higher content of A. 21 The proportion is relatively high, and the free water content is relatively low. White rice lacks the protection of the bran layer, and the exposed endosperm layer has more channels for water migration. Prolonged soaking leads to A... 22 and A 23 These changes, which account for a relatively high proportion, are of great guiding significance for optimizing the rice soaking process and improving the quality of cooked rice.

[0058] 5. Acquisition of images showing the moisture diffusion of layered milled rice during soaking.

[0059] Microscopic imaging system for acquiring images of soaked rice

[0060] The resonant frequency was 21 MHz, the magnet temperature was 35.0 ± 0.01 ℃, and the probe coil diameter was 10 mm. Rice was soaked in pure water, and transparent rice grains without cracks or spots were selected and drained. Individual grains were transferred to sample vials in NMR tubes. HSE sequence parameters were: SW = 40 kHz, Averages = 32, TR = 360 ms, TE = 2.63 ms, FOV = 50 mm. 50mm, Read Size=256, Phase Size=64, Echo Position=10%, using pseudo-color processing to convert the original image into an image.

[0061] Experimental results: such as Figure 11 As shown. The NMR image of unsoaked rice shows low signal intensity and a pale blue color. MD2, MD 12 When rice is soaked for 20 minutes, water exists only around the grains, with low moisture content around the brown rice. As soaking time increases, water gradually penetrates deeper into the grains. After 60 minutes of soaking, the signal inside the rice grains becomes noticeably redder, and the signal intensity increases. After 80 minutes of soaking, the image signal intensity is high. Water continues to penetrate into the rice grains, increasing the moisture content and expanding the water migration channels. After 120 minutes of soaking, the signal intensity is extremely high, indicating near-saturation in water absorption. MD 12 White rice showed the most significant penetration effect, followed by MD2 lightly milled rice, while MD0 brown rice had the worst effect, with moisture remaining at the germ attachment point.

[0062] In summary, during the soaking process, the surrounding moisture successively passes through the outer bran layer, inner bran layer, and endosperm layer barriers of the rice, eventually diffusing into the endosperm. Rice mainly diffuses into the endosperm through the ventral side of the rice grain and the germ attachment point; during the soaking process of brown rice, moisture mainly remains at the germ attachment point.

[0063] 6. Observation of the effect of soaking on the microstructure of layered milled rice

[0064] Soaked rice samples were pre-frozen at -80 °C for 10 h, then freeze-dried. The rice was gently cut with a blade, with unsoaked rice serving as a control group. The cross-sections were fixed to the stage with double-sided tape and sputtered with gold for approximately 90 s to form a gold layer about 10 nm thick. The cross-sections were then observed under a scanning electron microscope with an accelerating voltage of 15.0 kV.

[0065] Experimental results: such as Figure 12As shown, unsoaked rice with different milling degrees exhibited a smooth, dense, and crack-free cross-section. After soaking, all rice cross-sections showed varying degrees of honeycomb-like and cracked structures. The phenomenon was relatively stable for the first 60 minutes of soaking, with minimal cracking. After 80 minutes of soaking, wide and deep cracks appeared. Soaking allows water to continuously penetrate, loosening the structure between grains, dissolving some starch between cells and resulting in grooves and cracks. Starch granules also become loose and easily detached, and water migration channels are fully opened. The cracks were most severe after 120 minutes of soaking. The degree of cross-sectional cracking was not significantly affected by the milling degree; the loosening of the internal structure was related to the amount of water penetration. White rice showed deeper and wider cracks than brown rice. Unsoaked rice cross-sections showed a smooth, clustered starch granule structure that was tightly arranged, with the starch granules tightly wrapped within the cells by the cell walls.

[0066] 7. The effect of layered milling on the cooking characteristics of rice

[0067] The method for determining the cooking characteristics of rice was based on Lin Junfan's method (Lin Junfan, Zhao Liqi, Jia Yufeng, et al. Effects of milling degree on cooking, gelatinization characteristics, antioxidant activity and texture and sensory quality of red rice [J]. Food Industry Technology, 2020, 41(8): 250-255.), with slight modifications.

[0068] Experimental results: such as Figure 13 As shown, the color change of cooked rice is most obvious with a milling degree of 6% or less, while the appearance of cooked rice with a milling degree of more than 6% is not significantly different from that of white rice. The swelling phenomenon of the three types of brown rice is not obvious. Layered milling leads to more severe swelling, with particularly significant volume expansion, resulting in bent grains and obvious cracks and grooves on the ventral side, which contrasts with the appearance of brown rice. Brown rice and lightly milled rice are protected by the bran layer, resulting in lower saturated moisture content during cooking. Brown rice does not swell sufficiently, as the bran layer restricts endosperm swelling; white rice has its endosperm layer fully exposed, absorbing water fully and exhibiting significant swelling.

[0069] 7.1 Determination of Optimal Cooking Time for Rice

[0070] Weigh 5 g of rice, add 30 mL of deionized water to a 50 mL glass tube and heat in a water bath. After boiling for 20 min, at certain intervals, randomly take 5 grains of rice, place them on a glass plate, squeeze them and observe whether there is any ungelatinized starch core inside the rice grains. When 3 grains of rice have no white core, it is recorded as the optimal cooking time.

[0071] 7.2 Measurement of pH value of rice water

[0072] Weigh 1 g of rice, add 25 mL of deionized water and heat in a glass tube in a water bath. Stop heating when the optimal cooking time for each sample is reached, and then measure the pH value of the rice water after it cools naturally to room temperature.

[0073] 7.3 Determination of solids loss in rice soup

[0074] After cooking, wash the rice grains with hot water to remove any remaining dissolved substances. Combine the rice water with the rinsing water, then dry and weigh. The formula for calculating the loss of solids in the rice water is as follows: Rice water solids loss (mg / g) = (m 10 -m9) / m 11 m 10 m9 represents the weight (mg) of the aluminum box after drying to constant weight; m represents the weight (mg) of the aluminum box. 11 This indicates the weight (g) of the rice sample taken.

[0075] 7.4 Determination of Rice Extension Rate

[0076] The length of cooked rice and uncooked rice was measured using vernier calipers. The formula for calculating the elongation rate of cooked rice is as follows: Rice elongation rate (%) = (L1 / L2) 100% L1 represents the length of cooked rice (mm); L2 represents the length of uncooked rice (mm).

[0077] 7.5 Determination of Rice Expansion Rate

[0078] A 20 mL rice sample was measured using the volume displacement method. Excess deionized water was added, and the sample was placed in a 50 mL glass test tube. Samples of various milling degrees were cooked and cooled. The water was then drained using a strainer, and the volume of the cooked rice was measured using a graduated cylinder via volume displacement. The rice volume expansion rate (%) was calculated as follows: Rice volume expansion rate (%) = (V1 / V2) 100% V1 represents the volume of the cooked rice (cm³) 3 V2 represents the volume of raw rice (cm). 3 ).

[0079] 7.6 Determination of Iodine Blue Value of Rice

[0080] The method was modified slightly from that of Liu et al. (Liu Y, Shen W, Jin W, et al. Physicochemical characterization of a composite flour: blending purple sweet potato and riceflours[J]. Food Chemistry: X, 2024, 22: 101493.). 3 g of cooked rice was placed in a 50 mL centrifuge tube, 25 mL of deionized water was added, the mixture was incubated in a 40 ℃ water bath and shaken for 60 min, and the volume was adjusted to 50 mL. The mixture was then centrifuged at 3000 r / min for 15 min. 5 mL of the supernatant was collected, and 0.5 mL of 0.1 mol / L KI-I2 solution and 0.5 mL of 0.1 mol / L HCl were added. Distilled water was added and the volume was adjusted to 50 mL. After standing for 15 min, the absorbance was measured at 620 nm. A blank was prepared by adjusting the volume to 50 mL with 0.5 mL of 0.1 mL / L HCl and 0.5 mL of iodine reagent. The absorbance represents the iodine blue value.

[0081] The experimental results were measured three times. SPSS 25.0 and Microsoft Excel 2021 were used for data statistics and analysis, and one-way ANOVA, Tukey test and correlation analysis were performed. Origin 2022 software was used for graphing.

[0082] Experimental results: such as Figure 14 As shown, the cooking characteristics of rice are one of the important indicators reflecting the quality of cooked rice.

[0083] like Figure 14 As shown in Figure a, the optimal cooking time for the three types of rice decreases with increasing milling degree. Taking Anhui Jinyou as an example, the cooking time decreases from 33.28 min (MD0) to 22.45 min (MD0). 12 The decrease was 32.54%. P <0.05), the optimal cooking times for other types of rice are 28.25±0.09 min (MD2), 26.38±0.07 min (MD4), 24.56±0.35 min (MD6), 23.48±0.11 min (MD8), and 22.63±0.08 min (MD5). 10 This indicates a negative correlation between rice bran content and optimal rice cooking time. Notably, the cooking time for MD4 was 6.90 min shorter than that for MD0, and further increasing the milling fineness to 12% resulted in a 3.93 min reduction in time. PThe value <0.05 indicates that light milling significantly reduces the optimal cooking time. The optimal cooking times for Xinfeng No. 2 and Golden Sunny brown rice were 29.40 min and 28.03 min, respectively, while for white rice they were 18.59 min and 19.17 min. Rice with a milling degree of 4% or higher showed little change, indicating that once a gap is created in the dense bran layer, the rate of moisture diffusion increases rapidly, leading to a sharp reduction in the optimal cooking time. The cooking process of rice involves moisture diffusion into the rice grains and gradual starch gelatinization. Brown rice has a longer optimal cooking time because the hydrophobic layer on the surface of the bran layer can, to some extent, hinder moisture from entering the rice grains. Simultaneously, proteins and lipids bind with starch to form complexes, further limiting starch expansion and gelatinization. Milling damages the bran layer of brown rice, accelerating the cooking process due to rapid moisture diffusion and starch granule expansion, thus shortening the optimal cooking time.

[0084] like Figure 14 As shown in b, the elongation of cooked rice significantly increases with increasing milling degree. Taking Anhui Jinyou as an example, MD8 and MD... 12 There was no difference in the elongation rate of rice. P >0.05), the elongation rates of cooked rice at different milling degrees were 111.04±1.21% (MD0), 118.04±1.82% (MD2), 130.48±5.43% (MD4), 134.71±6.10% (MD6), 134.97±7.66% (MD8), and 138.05±6.56% (MD5). 10 ), 143.58±7.55% (MD 12 This indicates a positive correlation between milling degree and rice elongation rate, and the other two types of rice show the same trend. The rice elongation rate is ranked as follows: Henan Xinfeng No. 2 > Huangjinqing > Anhui Jinyou.

[0085] like Figure 14 As shown in c and d in the figure. Taking Anhui Jinyou as an example, the pH of rice water with different milling degrees were 7.13±0.05 (MD0), 7.22±0.08 (MD1), 7.35±0.06 (MD2), 7.38±0.04 (MD3), 7.44±0.05 (MD4), 7.45±0.03 (MD6), 7.58±0.06 (MD8), and 7.68±0.05 (MD9). 10 ), 7.74±0.11 (MD 12The results showed that rice is a weakly alkaline food (7.10-7.98), and the pH of rice water was correlated with the degree of milling. Because the bran layer of rice with a low degree of milling contains more fatty acids (long-chain carboxyl groups, which ionize into a small amount of hydrogen ions), it may have a certain impact on the pH of rice water. Brown rice is closer to neutral, but the pH of rice water in all rice samples was greater than 7.0. The solids loss in Anhui Jinyou rice water increased from 18.75±0.35 mg / g in MD0 to 57.80±3.11 mg / g in MD4, an increase of 208.27%. P <0.05). When the milling degree was 6%-10%, the loss of solids in cooked rice was 61.40±2.83 mg / g, 86.10±8.34 mg / g, and 97.80±0.71 mg / g, respectively, which was 59.80% higher than that of MD6. P >0.05), layered milling significantly increases the loss of solids in rice water ( P <0.05), MD 10 With MD 12 The concentrations were 97.80 ± 0.71 mg / g and 103.70 mg / g, respectively. P The increase was >0.05%, representing a 6.03% increase. The experimental results for the other two types of rice were consistent with the above findings. The results indicate that rice water is a weakly alkaline viscous liquid. The change in solids loss in rice water is significant for rice with a milling degree of 4% or lower, suggesting that light milling makes swelling more likely, leading to nutrient loss. Brown rice and lightly milled rice, due to the intact / partial bran layer protecting them, hinder the loss of contents, resulting in lower solids loss in their rice water.

[0086] like Figure 14 As shown in 'e', ​​the iodine blue value quantifies the amount of amylose dissolved in rice water. The results showed that Anhui Jinyou had a higher iodine blue value than Henan Xinfeng No. 2 and Huangjinqing, with a higher MD... 12 The highest values ​​reached 0.32055, 0.30907, and 0.26055 respectively, lower than the values ​​of brown rice (0.12611, 0.10606, and 0.10467). P The iodine blue values ​​of white rice (<0.05) were 154.18%, 191.41%, and 148.93% higher than those of brown rice, respectively. This is because the endosperm layer of white rice is fully exposed, making it easier for amylose in the rice to leach out. Additionally, indica rice has a higher amylose content than japonica rice. Lightly milled rice, protected by the bran layer, leachs less amylose, resulting in a lower iodine blue value, which is unrelated to the rice variety.

[0087] like Figure 14As shown in f, the volume expansion rate of Henan Xinfeng No. 2 MD0 was 276.5±4.95%. After grinding, the volume expansion rate showed an increasing trend, while there was no significant difference in volume expansion rate among the samples with grinding degrees of 4%-8%. P >0.05). The presence of the bran layer reduces the expansion rate of brown rice. This is because the dense structure and hydrophobic substances in the bran layer hinder water penetration into the rice grains. Simultaneously, the physical structure of the bran layer also restricts the water absorption and swelling of the starch in the rice grains, consistent with the results of soaking water absorption. The volume expansion rate of cooked rice is related to the degree of starch gelatinization and swelling, and the results of the volume expansion rate are consistent with the results of the rice elongation rate, further confirming the relevant conclusions. When the milling degree increases from 1% to 3%, the volume expansion rate of cooked rice increases from 316.00±8.49% to 342.50±2.12% (…). P <0.05), the increase was only 8.39%. When the milling degree continued to increase, the volume expansion rate of rice grains was between 342.50±2.12% and 419.50±0.95%, while MD4-MD 12 There is no difference between them. P >0.05), the other two types of rice showed consistent results with the above experiment. This indicates that only at milling degrees of 1% and 4%, the volume expansion rate increases rapidly after the bran layer breaks. Continuous milling does not significantly improve the volume expansion rate of cooked rice, while light milling can effectively improve the volume expansion rate of brown rice.

[0088] In summary, as the degree of rice milling increases, the optimal cooking time decreases, while the cooked rice elongation, rice water solids loss, iodine blue value, and heating volume expansion rate increase. Light milling can effectively improve the cooked and edible quality of brown rice, promoting nutrient dissolution and rice expansion, but excessive milling has very limited effect on improving the cooking characteristics of rice.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the water absorption characteristics and cooking quality of rice based on layered milling, characterized in that, Includes the following steps: Brown rice is milled in layers to obtain rice with good water absorption and cooking quality. The grinding degree of the layered grinding is 1~12%, and the grinding time is 47s~787s.

2. The method according to claim 1, characterized in that, The process involves layering and grinding followed by soaking, with the soaking time ranging from 0.25 to 8 hours.

3. The method according to claim 1, characterized in that, The rice includes japonica rice and indica rice. The japonica rice varieties include Henan Xinfeng No. 2 and Huangjinqing, and the indica rice varieties include Anhui Jinyou.

4. The method according to claim 1, characterized in that, The cooking quality includes optimal cooking time, rice water pH value, rice water solids loss, rice elongation rate, rice expansion rate, and rice iodine blue value.

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