Method for improving cooking quality of brown rice through microwave combined circulating water permeation pretreatment

Abstract

The invention discloses a method for improving the cooking quality of brown rice through microwave combined circulating water permeation pretreatment, and belongs to the technical field of food processing. The method comprises the following steps: firstly adjusting the initial moisture of brown rice, then carrying out circulating water permeation treatment and microwave treatment in sequence, controlling the single water spraying amount and the water treatment temperature, humidity and time, then carrying out microwave treatment, and then carrying out multiple times of circulation. Through the synergistic effect of the microwave heat effect and water permeation, on the premise that the cortex is kept intact, uniform gaps and efficient water channels are formed in the interface of the cortex and endosperm, insoluble dietary fibers are promoted to be converted into soluble dietary fibers, the content of resistant starch and slowly digestible starch is increased, the amylose content and the enthalpy value are reduced, and the dietary fiber content is improved. The heat stability of the starch paste is enhanced. The cooking time of the processed brown rice is shortened, the hardness is reduced, the elasticity is improved, and the sensory score reaches 80.47. The method is efficient, green, free of residues and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and more specifically to a method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment. Background Technology

[0002] Brown rice is a whole-grain food that retains the bran, germ, and endosperm of rice after hulling. It is rich in dietary fiber, polyphenols, vitamins, minerals, and functional components such as gamma-aminobutyric acid (GABA), and its nutritional value is significantly higher than that of refined white rice. Epidemiological studies have confirmed that long-term consumption of brown rice helps reduce the risk of chronic diseases such as type 2 diabetes and obesity. However, because the bran of brown rice contains a large amount of hydrophobic substances such as lignin, cellulose, and waxes, and has a dense structure, it is difficult for water to penetrate during cooking, requires a longer cooking time, and has a rougher texture, which seriously limits its acceptance by consumers.

[0003] To address the aforementioned issues, various brown rice pretreatment methods have been developed in the existing technology. Among these, chemical methods are prone to leaving chemical reagent residues, while biological methods are time-consuming and costly, making them unsuitable for industrial production. Physical methods, due to their high efficiency, environmental friendliness, and residue-free nature, have become a research hotspot. While microwave treatment can disrupt the dense structure of the bran and shorten cooking time through internal heating, it is prone to localized overheating, leading to problems such as grain cracking, uneven moisture distribution, and loss of heat-sensitive nutrients. Although circulating water permeation treatment can balance the moisture gradient and soften the bran through multiple micro-water replenishments, its efficiency as a standalone method is low, making it difficult to achieve significant structural modification in a short period.

[0004] Therefore, developing a pretreatment method that can efficiently disrupt the dense structure of brown rice bran while precisely controlling moisture distribution and preserving nutrients is of great significance for improving the cooking and edible quality of brown rice. Summary of the Invention

[0005] To address the shortcomings of existing brown rice pretreatment methods, this invention provides a method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment. This method utilizes the synergistic effect of microwave thermal effect and circulating water permeation to regulate moisture, creating a uniform gap between the bran and endosperm while maintaining the integrity of the bran, thus constructing an efficient moisture channel and significantly improving the cooking characteristics and edible quality of brown rice.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] First, this invention provides a method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment, comprising the following steps:

[0008] Step 1: Adjust the initial moisture content of the brown rice raw material;

[0009] Step 2: Spray deionized water evenly onto the surface of the brown rice after Step 1, stir well, and then place it in a constant temperature and humidity chamber for 60 minutes.

[0010] Step 3: Spread the brown rice processed in Step 2 into a single layer and microwave it.

[0011] Step 4: Repeat steps 2 and 3 to obtain the processed brown rice.

[0012] Preferably, in step one, the initial moisture content of the brown rice raw material is adjusted to 13.0 ± 0.1%.

[0013] Preferably, the amount of water sprayed in step two is 1.0% of the mass of the brown rice.

[0014] Preferably, the temperature and relative humidity chamber in step two is 25°C and 85% respectively.

[0015] Preferably, the microwave processing power in step three is 450 W, and the processing time for a single cycle is 30 s.

[0016] Preferably, in step four, the operations of steps two and three are repeated for a total of four cycles.

[0017] The present invention also provides brown rice prepared by the above method.

[0018] The present invention also provides the application of the above-described method or the above-described brown rice in the preparation of low glycemic index whole grain foods.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment, which has the following beneficial effects:

[0020] This invention utilizes the synergistic effect of microwave and circulating water penetration to form uniform physical gaps and efficient water penetration channels at the interface between the bran and endosperm, while maintaining the integrity of the brown rice bran. This significantly shortens the optimal cooking time and improves the uniformity of water absorption.

[0021] The method of this invention effectively promotes the conversion of insoluble dietary fiber in brown rice into soluble dietary fiber, reduces the content of amylose, increases the content of resistant starch and slow-digesting starch, enhances the thermal stability of starch paste, and endows the product with good glycemic regulation potential.

[0022] Brown rice treated by the method of this invention has a 53.4% ​​lower hardness and a 16.4% higher elasticity after steaming and cooking, resulting in a sensory score of 80.47 points and a significant improvement in eating quality.

[0023] The method of this invention is a physical pretreatment that leaves no chemical reagent residue, is simple to operate, and is easy to implement for continuous industrial production, thus having good market application prospects. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 Scanning electron microscope images of brown rice with different pretreatments;

[0026] Figure 2 XRD patterns of brown rice with different pretreatments;

[0027] Figure 3 The textural properties of brown rice after cooking with different pretreatments. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment. The specific steps are as follows:

[0031] (1) Raw material preparation: Select "Jihong No. 6" brown rice, remove impurities, and adjust the initial moisture content to 13.0±0.1%;

[0032] (2) First circulating water permeation treatment: Accurately weigh 200g of brown rice sample, and spray deionized water evenly onto the surface of the brown rice using a spray bottle. The amount of water sprayed is 1.0% (i.e. 2.0g) of the mass of the brown rice. After stirring thoroughly, put it into a self-sealing bag and seal it. Place it in a constant temperature and humidity chamber and let it stand for 60 min at 25℃ and 85% relative humidity.

[0033] (3) First microwave treatment: Spread the brown rice treated in step (2) in a single layer on a tray, treat it at 450W microwave power for 30s, and then take it out and cool it to room temperature;

[0034] (4) Cyclic processing: Repeat steps (2) and (3) for a total of four cycles to obtain the pretreated brown rice sample (MW-CWIBR).

[0035] Comparative Example 1

[0036] Unprocessed group

[0037] The same "Jihong No. 6" brown rice as in Example 1 was selected and used as the untreated control group (UBR) without any pretreatment.

[0038] Comparative Example 2

[0039] Single microwave processing group

[0040] The same brown rice as in Example 1 was selected and subjected to microwave treatment only: it was continuously treated at 450W microwave power for 120s to obtain the MWBR sample.

[0041] Comparative Example 3

[0042] One-time water spray combined with microwave treatment group

[0043] The same brown rice as in Example 1 was selected and subjected to a single water spray combined with microwave treatment: 4.0% of the brown rice mass of deionized water was sprayed at once, followed by continuous treatment at 450W microwave power for 120s to obtain the WS-MWBR sample.

[0044] Experimental Example

[0045] I. Experimental Methods

[0046] (1) Determination of moisture content of brown rice: The determination was carried out in accordance with the first method (direct drying method) in the national standard 5009.3-2016 "Determination of moisture in food".

[0047] (2) Scanning electron microscopy observation of brown rice: After the sample was vacuum sputtered and gold-plated, the microstructure was observed using a scanning electron microscope. The accelerating voltage was 5kV and the vacuum degree was 5×10. -5 mbar, tested using an SE2 probe.

[0048] (3) Determination of dietary fiber content in brown rice: The total dietary fiber (TDF), soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) in brown rice were determined in accordance with the national standard GB 5009.88-2023 "Determination of dietary fiber in food".

[0049] (4) Determination of total starch content, amylose content and resistant starch content in brown rice: Total starch content (TSC) was determined according to the first method (enzymatic hydrolysis method) in the national standard GB 5009.9-2023 "Determination of starch in food"; Amylose content (AC) was determined according to the first method (defatting method) in the national standard GB / T 15683-2025 "Determination of amylose content in rice"; Resistant starch content (RSC) was determined according to AOAC 2002.02 "Resistant starch in starch and plant matrix digestion method".

[0050] (5) Determination of in vitro digestibility of brown rice: The rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) of brown rice with different pretreatments were determined. The relative contents of RDS, SDS, and RS were calculated according to formulas (1)-(3):

[0051] (1)

[0052] (2)

[0053] (3)

[0054] Where: G0, G 20 G 120 The values ​​represent the glucose release (mg) of the samples at 0, 20, and 120 min of reaction, respectively; 0.9 is the glucose-starch conversion factor.

[0055] (6) X-ray diffraction determination of brown rice: After the brown rice was pulverized, it was passed through an 80-mesh sieve. The brown rice powder was then placed on a grooved glass plate, flattened, and measured using an X-ray diffraction (XRD) instrument. The scanning conditions were: voltage 40 kV, current 40 mA, Cu-Kα radiation (λ = 0.154 nm), scanning angle 2θ = 5°-50°, step size 0.01°, and scanning speed 2° / min. The relative crystallinity was calculated using Jade 6.5 software.

[0056] (7) Gelatinization characteristics of brown rice flour: Brown rice was pulverized by a hammer mill and then passed through a 100-mesh sieve to prepare brown rice flour. The gelatinization characteristics were determined using a Rapid Visco Analyzer (RVA). 3.0 g of brown rice flour was accurately weighed and thoroughly mixed with 25 mL of distilled water before immediate measurement. The measurement procedure was as follows: initial heating to 50 °C and holding for 1 min, then heating to 95 °C at 12 °C / min and holding for 2.5 min, followed by cooling to 50 °C at 12 °C / min and holding for 2 min.

[0057] (8) Thermal properties of brown rice flour: Accurately weigh 4.0 mg of brown rice flour into a crucible, add 10 μL of distilled water, mix thoroughly, seal, and let stand overnight at room temperature to equilibrate. Use a blank crucible as a blank control, and analyze the thermal properties of the sample using a differential scanning calorimeter (DSC). The heating range is 25-120℃, and the heating rate is 10℃ / min.

[0058] (9) Texture characteristics of brown rice: After the brown rice was cooked and cooled to room temperature, three grains of brown rice were randomly selected each time and analyzed using a texture analyzer. The instrument parameters were set as follows: probe model P / 36R, pre-test speed 5.00 mm / s, test speed 0.50 mm / s, post-test speed 5.00 mm / s, trigger force 5.0 g, interval between two compressions 5 s, and compression degree 75%. Each sample was measured 10 times, and the average value was used for subsequent analysis.

[0059] (10) Determination of the cooking characteristics of brown rice:

[0060] Optimal cooking time determination: The glass plate-white core method was used. 10g of brown rice sample was accurately weighed, soaked in deionized water at room temperature for 10 minutes, drained, and then boiled in boiling water for 15 minutes. Afterward, 10 grains of brown rice were taken out every 1 minute, placed between two glass plates, and gently pressed for observation. The cooking time when all brown rice grains showed no white core was the optimal cooking time.

[0061] Water absorption rate determination: Accurately weigh 5g of brown rice sample, soak it in deionized water at room temperature for 10 min, drain the water, add it to 100mL of boiling water, cook for the above-mentioned optimal cooking time, remove the residual water on the surface, cool to room temperature and weigh accurately, and calculate the water absorption rate according to formula (4):

[0062] (4)

[0063] Volume expansion rate determination: Accurately weigh 5g of brown rice sample, determine its volume before cooking using the water displacement method, then process the sample according to the water absorption rate determination method described above. After processing, determine its volume after cooking using the water displacement method as well, and calculate the volume expansion rate according to formula (5):

[0064] (5)

[0065] Solid loss rate: After treating brown rice according to the water absorption rate determination method, the cooked brown rice grains were removed, and the surface residue of the rice grains was rinsed several times with a small amount of deionized water. The cooking water and rinsing water were combined and transferred to a pre-weighed beaker. The beaker was then dried in an oven at 103±2℃ until constant weight. The mass of solids in the rice water was calculated, and the solid loss rate was calculated according to formula (6):

[0066] (6)

[0067] (11) Sensory quality determination: The sensory quality of brown rice with different pretreatments was evaluated in accordance with the recommended national standard GB / T 15682-2008 "Sensory evaluation method for cooking and eating quality of rice and paddy".

[0068] The above experimental data should be repeated at least three times, so that... Data were analyzed using SPSS 24.0 software, and the Duncan test was used to test for statistical significance. A p-value < 0.05 was considered statistically significant. Data processing and plotting were performed using Origin 2023 and Jade 6.5.

[0069] II. Results Statistics

[0070] (1) Effects of different pretreatments on brown rice bran

[0071] The composition and content of dietary fiber are shown in Table 1:

[0072] Table 1. Dietary fiber content (dry basis) of brown rice with different pretreatments

[0073] sample TDF / % SDF / % IDF / % UBR <![CDATA[4.90±0.04 a ]]> <![CDATA[1.23±0.01 d ]]> <![CDATA[3.67±0.05 a ]]> MWBR <![CDATA[4.89±0.02 a ]]> <![CDATA[1.35±0.05 c ]]> <![CDATA[3.54±0.03 b ]]> WS-MWBR <![CDATA[4.89±0.02 a ]]> <![CDATA[1.68±0.08 b ]]> <![CDATA[3.21±0.03 c ]]> MW-CWIBR <![CDATA[4.91±0.03 a ]]> <![CDATA[1.89±0.06 a ]]> <![CDATA[3.02±0.01 d ]]>

[0074] Note: Different letters in the same column indicate significant differences (p < 0.05), the same applies below.

[0075] Dietary fiber analysis showed no significant difference in TDF content among UBR, MWBR, WS-MWBR, and MW-CWIBR. Compared with UBR, the TDF content of other pretreatment groups showed no significant change (p>0.05), but the SDF and IDF contents differed significantly (p<0.05). This indicates that microwave treatment did not change the TDF content in brown rice, but it altered its form. Compared with MWBR, the SDF content of brown rice after water treatment was further increased. This is because in the MW-CWI process, water molecules can penetrate into the intermolecular gaps of brown rice dietary fiber, disrupting some glycosidic bonds and promoting the conversion of insoluble fiber to soluble fiber. The thermal effect of microwaves further intensifies the breakdown of fiber molecules, causing more IDF to be converted into SDF. The synergistic effect of the two treatments significantly increased the SDF content and decreased the IDF content, reducing its hindering effect on water absorption and starch gelatinization during rice cooking, thereby improving the texture of brown rice.

[0076] Microscopic morphology and interfacial structure characteristics of brown rice:

[0077] Scanning electron microscopy results of brown rice bran after different pretreatments are as follows: Figure 1 As shown in (AD), the cortex surface (A1, A2) of UBR exhibits a continuous, dense, and smooth sheet-like structure without obvious damage or depressions; the cortex and endosperm interface (A3, A4) are tightly bonded without gaps, a structural feature consistent with the natural state of untreated brown rice. The cortex surface (B1, B2) of MWBR shows large-area damage, wrinkles, and cracks; in the cross-section (B3-B4), the cortex is fragmented and detached, and the interface between the cortex and endosperm is disrupted. This is because the thermal effect of microwaves causes rapid vaporization of internal moisture in the brown rice, and the resulting vapor pressure directly damages the dense structure of the cortex. The cortex surface (C1, C2) of WS-MWBR shows localized damage and wrinkles, but the degree of damage is weaker than that of MWBR; slight gaps appear at the cortex and endosperm interface (C3, C4). This indicates that water spray pretreatment softens the cortex by absorbing water beforehand, reducing the vapor pressure impact during microwave heating, thereby mitigating the degree of structural damage. The cortical surfaces (D1, D2) of the MW-CWIBR exhibit only slight localized depressions, and the cortical structure remains relatively intact. However, significant and uniform gaps are formed at the cortical-endosperm interface (D3, D4). The MW-CWI process, through repeated water absorption and dehydration, allows the cortex to absorb water uniformly and gradually soften, enabling microwave energy to act more gently on the cortical-endosperm interface. This promotes a moderate weakening of the interfacial bonding, ultimately creating gaps that facilitate water penetration.

[0078] (2) Effects of pretreatment on the structure and digestibility of brown rice flour

[0079] The changes in the composition and crystal structure of brown rice starch are shown in Table 2:

[0080] Table 2. TSC, AC and RSC content in brown rice flour (dry basis)

[0081] sample TSC / % AC / % RSC / % UBR <![CDATA[71.94±0.21 a ]]> <![CDATA[15.71±0.12 a ]]> <![CDATA[2.47±0.09 d ]]> MWBR <![CDATA[71.88±0.30 a ]]> <![CDATA[15.68±0.20 b ]]> <![CDATA[6.54±0.12 c ]]> WS-MWBR <![CDATA[71.74±0.17 a ]]> <![CDATA[15.55±0.11 c ]]> <![CDATA[12.80±0.13 b <!-- 5 -->]]> MW-CWIBR <![CDATA[72.02±0.13 a ]]> <![CDATA[15.47±0.17 d ]]> <![CDATA[15.87±0.17 a ]]>

[0082] Table 2 shows that different pretreatment methods had no significant effect on the TSC content of brown rice (p > 0.05). This is mainly because microwave pretreatment alters the aggregated structure of starch, while circulating water pretreatment promotes microwave energy conduction and avoids starch degradation caused by local overheating. Neither pretreatment changed the chemical composition of starch, so there was no significant difference in TSC content among the pretreatment groups (p > 0.05). The pretreatment methods had a significant difference in effect on AC content (p < 0.05), showing a decreasing trend. This is related to the synergistic effect of microwave-induced starch molecule recombination and pretreatment. The thermal effect of microwave treatment destroys the crystalline structure of starch granules, causing some amylose molecules to dissolve from the inside of the granules and combine with lipids to form starch-lipid complexes, resulting in a decrease in the detection value of free amylose. MWBR only loosens the surface structure of starch granules, and the amount of amylose dissolved is not large, so its content decreases the least. MW-CWIBR, on the other hand, constructs a moisture gradient through MW-CWI, allowing microwave energy to be uniformly transferred to the inside of starch granules, enabling more complete recombination of the internal structure of starch granules. The reduction in amylose content can decrease the hardness of brown rice after cooking, improving its texture. After pretreatment, the RSC content significantly increased (p < 0.05), with MW-CWIBR showing significantly higher levels than other treatment groups. During the microwave cooling stage, starch molecular chains rearranged under the influence of a moisture gradient to form a dense crystalline structure, promoting the formation of indigestible RS3-type starch.

[0083] XRD patterns of brown rice with different pretreatments are as follows: Figure 2 As shown, all treatment groups exhibited characteristic peaks at 2θ≈15°, 17°, 18°, and 23°, consistent with the typical characteristics of starch type A crystal structure. A weak absorption peak appeared at 2θ≈20°, corresponding to the V-shaped crystal structure of the starch-lipid complex, indicating that naturally occurring lipids in brown rice formed a complex with starch. However, the characteristic peak intensities varied significantly among different samples, indicating that starch crystallinity and crystal size were affected, leading to changes in diffraction intensity. Crystallinity measurements showed that the crystallinities of UBR, MWBR, WS-MWBR, and MW-CWIBR were 36.8%, 28.2%, 34.3%, and 36.0%, respectively. Compared to UBR, the circulating water treatment slightly reduced crystallinity because the uniformly permeated water alleviated microwave thermal stress, and multiple short-duration microwave treatments avoided concentrated damage to the crystallizing region from continuous high temperatures, ultimately preserving a more complete ordered structure.

[0084] In vitro digestion characteristics analysis:

[0085] Table 3 shows the effects of different pretreatment methods on the in vitro digestibility of brown rice.

[0086] Table 3. In vitro digestibility of brown rice with different pretreatments (dry basis)

[0087] sample RDS / % SDS / % RS / % UBR <![CDATA[46.78±0.30 a ]]> <![CDATA[23.74±0.12 d ]]> <![CDATA[1.78±0.10 d ]]> MWBR <![CDATA[37.63±0.25 b ]]> <![CDATA[29.91±0.14 c ]]> <![CDATA[5.43±0.11 c ]]> WS-MWBR <![CDATA[27.87±0.18 c ]]> <![CDATA[35.35±0.13 b ]]> <![CDATA[10.69±0.10 b ]]> MW-CWIBR <![CDATA[20.92±0.26 d ]]> <![CDATA[40.82±0.15 a ]]> <![CDATA[12.85±0.14 a ]]>

[0088] The results showed that MW-CWI significantly altered the in vitro digestibility of brown rice flour, significantly increasing RDS content (p<0.05) and SDS and RS content (p<0.05). Compared to traditional conductive heating, the internal heat effect generated by microwave heating caused specific reconstruction of the internal structure of brown rice grains, hindering the catalytic hydrolysis of starch molecules by amylase. Water, as a heat transfer medium, promoted the formation of microwave-induced starch-lipid complexes. The uniform water gradient constructed by circulating water permeation ensured uniform microwave energy transmission, avoiding excessive starch degradation caused by localized overheating. Simultaneously, it promoted the formation of porous structures on the surface of starch granules. While these porous structures improved water absorption efficiency, they also formed physical barriers, delaying the penetration of amylase into the starch granules. Furthermore, MW-CWI caused repeated water absorption and dehydration of brown rice grains, promoting the expansion of amorphous regions within the starch granules and partially disrupting the crystalline structure, forming more indigestible crystalline structures and further reducing RDS content.

[0089] Compared with UBR, MWBR, WS-MWBR, and MW-CWIBR all showed significantly higher SDS and RS contents (p<0.05), with SDS contents of 23.74%, 29.91%, 35.35%, and 40.82%, respectively. The digestibility was in the order of MW-CWIBR > WS-MWBR > MWBR > UBR. The increased SDS content was mainly due to the gradient modification of starch structure by pretreatment, transforming the starch structure from "easily digestible and rapidly digestible" to "slowly digestible." Microwave treatment caused localized gelatinization and structural damage to starch granules, with some starch chains forming moderately ordered crystalline structures during subsequent rearrangement. Because its crystallinity was higher than that of amorphous RDS but lower than that of RS, this structure could be slowly hydrolyzed by amylases, ultimately exhibiting the characteristics of SDS. WS-MW, through prehydration, caused the starch granules to expand prematurely, providing more sufficient molecular fluidity for microwave-induced starch structural recombination, thus improving the efficiency of forming moderately crystalline structures. MW-CWI, through dynamic moisture transfer via circulating water infiltration, makes the moisture distribution inside starch granules more uniform, the starch chain rearrangement more orderly, and the proportion of medium crystallinity structure maximized, thereby further increasing the SDS content.

[0090] The increased RS content is mainly due to the combined effect of microwave thermal effect and water transfer, which promotes starch chain rearrangement to form a denser and more ordered crystalline structure. This highly crystalline structure can form a stronger physical barrier, significantly resisting the catalytic hydrolysis of amylase. As a water-soluble dietary fiber, RS, in addition to lowering the glycemic index, can also be fermented by microorganisms in the large intestine to produce short-chain fatty acids, improving the gut microbiota structure. This gives MW-CWIBR multiple functions, including blood sugar regulation, weight management, and gut health protection.

[0091] (3) Effects of different pretreatments on the physicochemical properties of brown rice

[0092] The changes in gelatinization properties are shown in Table 4:

[0093] Table 4. Gelatinization characteristics of brown rice under different pretreatments

[0094] sample Peak viscosity / cP Final viscosity / cP Disintegration value / cP Resurrection Value / cP UBR <![CDATA[2894±32 a ]]> <![CDATA[3281±66 a ]]> <![CDATA[1274±72 a ]]> <![CDATA[1661±50 a ]]> MWBR <![CDATA[3117±26 b ]]> <![CDATA[3414±75 b ]]> <![CDATA[1074±51 b ]]> <![CDATA[1371±47 b ]]> WS-MWBR <![CDATA[3258±22 c ]]> <![CDATA[3556±51 c ]]> <![CDATA[814±12 c ]]> <![CDATA[1112±82 c ]]> MW-CWIBR <![CDATA[3478±19 d ]]> <![CDATA[4210±27 d ]]> <![CDATA[104±7 d ]]> <![CDATA[836±26 d ]]>

[0095] As shown in Table 4, the peak viscosity (3478±19 cP) and final viscosity (4210±27 cP) of MW-CWIBR were significantly higher than those of the other three groups (p<0.05), indicating that MW-CWI treatment had the best effect on improving starch swelling and paste stability. The circulating water, through intermittent replenishment, formed uniform and dense moisture channels in the brown rice bran layer, thus avoiding the particle cracking and uneven moisture distribution problems caused by single soaking with WS-MWBR. Simultaneously, microwave treatment further disrupted the A-type crystalline structure of starch, enhanced the fluidity of starch chains, promoted uniform swelling of starch particles, and prevented aggregation, ultimately resulting in a significant increase in viscosity.

[0096] The disintegration value reflects the shear resistance of starch paste at high temperatures. A lower disintegration value indicates stronger thermal stability of the starch paste. The disintegration value of the MW-CWIBR treatment group was significantly lower than the other three groups (p<0.05), a 92% reduction compared to UBR. This indicates that MW-CWI treatment significantly enhances the thermal stability of starch granules, making them less prone to disintegration during heating. Microwave treatment can cause partial pregelatinization of starch granules, forming a stable gel structure, thereby reducing the disintegration value. In this invention, on the one hand, the circulating water penetration during the MW-CWI process ensures uniform microwave energy conduction, avoiding localized overheating that could lead to starch granule breakage and reducing the disordered breakage of starch chains under shear. On the other hand, microwave treatment induces partial gelatinization and rearrangement of starch molecules, forming a cross-linked structure. The circulating water penetration further promotes the interaction between starch and lipids / proteins, forming starch-lipid complexes. These complexes can fill the gaps between starch granules, enhancing their rigidity and forming a more stable gel network, further resisting structural damage caused by high-temperature shear. Ultimately, this makes the starch paste less prone to disintegration at high temperatures, significantly enhancing its thermal stability.

[0097] The retrogradation value reflects the degree of recrystallization of amylose after cooling. A lower value indicates a weaker ability of amylose molecules to rearrange and form crystals, resulting in a lower risk of hardening and deterioration in product quality during storage. Table 4 shows that the retrogradation value of the MWBR group was significantly lower (p<0.05). Microwave treatment can cause amylose molecules to rearrange, forming a structure that is less prone to crystallization, thus reducing the retrogradation value. The retrogradation values ​​of WS-MWBR and MW-CWIBR continued to decrease (p<0.05), with the MW-CWIBR group showing a 63.1% reduction compared to UBR. This is because the circulating water permeation pretreatment fully hydrates the starch granules, and the starch-lipid complex formed after microwave heating effectively inhibits the re-aggregation of amylose molecules. Simultaneously, the B-type retrogradation crystal structure induced by the composite treatment is stable and not easily rearranged, thus significantly inhibiting starch retrogradation and providing favorable conditions for extending the shelf life of brown rice products.

[0098] The changes in thermal properties are shown in Table 5:

[0099] Table 5 Thermal properties of brown rice with different pretreatments

[0100] sample Starting temperature / ℃ Peak temperature / °C End temperature / ℃ Enthalpy (J / g) UBR <![CDATA[64.5±0.3 a ]]> <![CDATA[72.3±0.4 a ]]> <![CDATA[82.4±0.1 a ]]> <![CDATA[9.37±0.21 a ]]> MWBR <![CDATA[66.4±0.4 b ]]> <![CDATA[73.8±0.6 b ]]> <![CDATA[83.7±0.2 b ]]> <![CDATA[6.74±0.14 b ]]> WS-MWBR <![CDATA[67.2±0.2 c ]]> <![CDATA[74.5±0.5 c ]]> <![CDATA[84.9±0.4 c ]]> <![CDATA[5.81±0.11 c ]]> MW-CWIBR <![CDATA[68.6±0.3 d ]]> <![CDATA[76.4±0.4 d ]]> <![CDATA[85.8±0.2 d ]]> <![CDATA[4.59±0.15 d ]]>

[0101] Thermal properties are core indicators reflecting the stability of the crystalline structure and gelatinization energy requirements of brown rice starch. The effects of pretreatment on the arrangement and crystalline state of starch molecules are directly revealed by measuring the initial gelatinization temperature, peak gelatinization temperature, final gelatinization temperature, and enthalpy using DSC. Table 5 shows the influence of different pretreatment methods on the thermal properties of brown rice flour. Compared with UBR, MWBR, WS-MWBR, and MW-CWIBR all significantly altered the initial gelatinization temperature, peak gelatinization temperature, final gelatinization temperature, and gelatinization enthalpy change of starch (p<0.05). The increase in gelatinization temperature indicates that the internal structure of the starch granules becomes more compact after pretreatment, requiring higher temperatures to disrupt the crystalline regions and initiate the gelatinization process. UBR's starch crystallization regions exist in a naturally loose state with weak intermolecular forces, requiring a lower melting temperature. MWBR, through volumetric heating, creates cracks on the surface of starch granules and induces partial gelatinization and rearrangement of starch molecular chains, increasing the density of the crystalline regions and thus raising the gelatinization temperature. WS-MWBR's static moisture replenishment further promotes starch-lipid and starch-protein interactions. These complexes, together with the dense crystalline regions, enhance the binding force between starch molecules, causing the gelatinization temperature to rise continuously. MW-CWIBR's dynamic moisture penetration effect makes the starch crystalline regions reconstructed more uniformly and denser, and moisture, as a heat transfer medium, strengthens intermolecular cross-linking, ultimately achieving the highest gelatinization temperature.

[0102] Enthalpy reflects the total amount and integrity of starch crystallization zones. UBR starch crystals have an intact structure with no obvious damage, hence the highest enthalpy. MWBR only partially destroys A-type crystals, leaving more residual crystallization zones, resulting in a limited decrease in enthalpy. In WS-MWBR, the soaking treatment loosens the cortex, promoting water penetration, and the microwaves more thoroughly destroy the crystallization zones, further reducing the enthalpy. In MW-CWIBR, circulating water penetration achieves uniform water distribution, allowing microwave energy to act evenly on each starch granule. The crystallization zones are fully destroyed and reorganized into B-type crystals, reducing the total amount of residual crystallization zones, hence the lowest enthalpy.

[0103] Changes in texture properties:

[0104] The textural properties of cooked brown rice after different pretreatments are as follows: Figure 3 As shown, all treatments significantly reduced the hardness of brown rice. Figure 3 A) Adhesion ( Figure 3 C) Adhesion ( Figure 3 D) and chewing ( Figure 3 F). MW-CWIBR exhibited the lowest hardness, decreasing by 53.4% ​​compared to UBR. This is attributed to the formation of gaps between the bran and endosperm due to the penetration of circulating water, resulting in a looser grain structure and significantly reduced hardness. The absolute value of the adhesiveness of MW-CWIBR increased by 188.9% compared to UBR, indicating that MW-CWI treatment promotes the dissolution of amylose, enhancing the adhesion of the rice grain surface after cooking, thus exhibiting more significant negative adhesiveness. Water spray pretreatment improved the elasticity of brown rice, with MW-CWIBR showing a 16.4% increase in elasticity compared to UBR, but there was no significant difference between MWBR and WS-MWBR (p > 0.05). Furthermore, UBR exhibited the highest chewiness, while MW-CWIBR showed a 19.1% decrease in chewiness compared to UBR, indicating that compared to the other two pretreatments, MW-CWI is more conducive to the softening of brown rice grains through water absorption, thus improving texture.

[0105] (4) Effects of different pretreatments on the cooking and eating quality of brown rice

[0106] The results of the brown rice cooking quality test are shown in Table 6:

[0107] Table 6. Cooking quality of brown rice with different pretreatments

[0108] sample Optimal cooking time / min Water absorption rate / % Volume expansion rate / % Solid loss rate / % Sensory rating UBR <![CDATA[28.5±1.0 a ]]> <![CDATA[232.6±2.4 d ]]> <![CDATA[248.9±2.5 d ]]> <![CDATA[3.21±0.08 d ]]> <![CDATA[57.12±0.2 d ]]> MWBR <![CDATA[25.4±0.8 b ]]> <![CDATA[257.8±3.2 c ]]> <![CDATA[310.5±3.0 c ]]> <![CDATA[3.34±0.06 c ]]> <![CDATA[64.14±0.4 c ]]> WS-MWBR <![CDATA[23.6±0.5 c ]]> <![CDATA[298.2±3.5 b ]]> <![CDATA[360.7±2.8 b ]]> <![CDATA[3.47±0.03 b ]]> <![CDATA[72.75±0.1 b ]]> MW-CWIBR <![CDATA[21.4±0.6 d ]]> <![CDATA[310.4±2.8 a ]]> <![CDATA[410.8±4.1 a ]]> <![CDATA[3.58±0.07 a ]]> <![CDATA[80.47±0.5 a ]]>

[0109] Different pretreatment methods significantly affected the optimal cooking time, water absorption rate, volume expansion rate, solids loss rate, and sensory score of brown rice (p < 0.05). Compared with UBR, the optimal cooking time of MWBR, WS-MWBR, and MW-CWIBR was significantly shortened (p < 0.05). This is because UBR has a dense bran and intact endosperm starch crystals, resulting in high resistance to water and heat penetration and prolonged cooking time; while after treatment, gaps are formed between the bran and endosperm, providing a rapid water penetration channel. At the same time, the starch crystal structure is more easily gelatinized after microwave modification, thus shortening the cooking time. The water absorption rate and volume expansion rate of MW-CWIBR were increased by 33.5% and 64.9% respectively compared with UBR, significantly higher than the other two treatment groups. After cooking, the solids loss rate increased in all treatment groups. This is because the starch granules became looser after pretreatment, allowing some amylose and soluble sugars to dissolve during cooking. However, due to the relatively intact cortex structure, the solids loss rate increased slightly while maintaining improved cooking quality. The sensory score of MW-CWIBR was significantly higher than that of UBR and markedly higher than other treatment groups (p < 0.05). Sensory score and textural characteristics ( Figure 3 Directly related to this, MW-CWIBR's low hardness, high elasticity, and stickiness make the rice grains softer, stickier, and more palatable after steaming. The shortened optimal steaming time reduces the risk of over-gelatinization of the rice grains, further improving the edible quality of brown rice.

[0110] Based on the above experimental research and analysis, this invention addresses the core problems of low cooking efficiency and rough texture caused by the dense bran of brown rice by proposing the MW-CWI pretreatment technology. This technology, through the synergistic effect of thermal effects and moisture gradients, creates uniform physical gaps and moisture penetration channels at the bran-endosperm interface without damaging the integrity of the bran, significantly improving the physicochemical properties and eating quality of brown rice. Brown rice treated with the MW-CWI process achieves effective conversion of IDF to SDF without changing the TDF content. Simultaneously, the starch molecules inside the brown rice undergo orderly recombination under microwave induction, increasing the resistant starch (RS) content to 15.87% and the slow-digesting starch (SDS) content to 40.82%, giving the product excellent glycemic control potential. Furthermore, the MW-CWI technology enhances the thermal stability of starch granules and effectively inhibits starch retrogradation. In terms of eating quality, MW-CWIBR significantly improved water absorption efficiency. Compared with the untreated group, the hardness of brown rice was reduced by 53.4%, and its elasticity and stickiness were significantly enhanced. The optimal cooking time was shortened to 21.4 minutes, and the sensory score was improved to 80.47 points.

[0111] The MW-CWI pretreatment technology of this invention not only retains the nutritional advantages of brown rice itself, but also improves its cooking characteristics and eating quality. It is also characterized by high efficiency, greenness, no chemical residues, and easy large-scale promotion, providing theoretical support and practical reference for the innovation and industrial application of brown rice pretreatment technology.

[0112] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment, characterized in that, Includes the following steps: Step 1: Adjust the initial moisture content of the brown rice raw material; Step 2: Spray deionized water evenly onto the surface of the brown rice after Step 1, stir well, and then place it in a constant temperature and humidity chamber for 60 minutes. Step 3: Spread the brown rice processed in Step 2 into a single layer and microwave it. Step 4: Repeat steps 2 and 3 to obtain the processed brown rice.

2. The method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment according to claim 1, characterized in that, In step one, the initial moisture content of the brown rice raw material is adjusted to 13.0 ± 0.1%.

3. The method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment according to claim 1, characterized in that, In step two, the amount of water sprayed in a single application is 1.0% of the mass of the brown rice.

4. The method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment according to claim 1, characterized in that, The temperature and humidity chamber mentioned in step two is 25℃ and 85% relative humidity.

5. The method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment according to claim 1, characterized in that, In step three, the microwave processing power is 450 W, and the processing time for a single cycle is 30 s.

6. The method for improving the cooking quality of brown rice through microwave combined with circulating water permeation pretreatment according to claim 1, characterized in that, Step four involves repeating the operations of steps two and three for a total of four cycles.

7. Brown rice prepared by the method according to any one of claims 1-6.

8. The use of brown rice obtained by the method of any one of claims 1-6 or the brown rice of claim 7 in the preparation of low glycemic index whole grain foods.

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