A method for processing high-value brown rice

Abstract

This invention relates to a high-value brown rice processing method, belonging to the field of grain deep processing technology. The high-value brown rice processing method of this invention includes: placing brown rice into a rice milling machine, controlling the bran removal rate of each pass to 0.5-2.0% by adjusting the milling current and running time, so that the bran removal rate reaches 20-25%; collecting rice and bran from each pass, and calculating the milling loss rate for each pass; selecting brown rice and rice from odd or even passes, and measuring the bran retention, nutrient content, and quality characteristics to determine the optimal milling rate; then measuring the metal element content, alkyl resorcinol, and phytic acid content of the bran from each pass before the optimal milling loss rate, and performing significance analysis; determining the layered structure and layer markers of the bran based on the main enrichment areas, and dividing it into different structural layers; and finally, collecting the bran from different structural layers for subsequent high-value utilization based on the milling loss rate corresponding to each structural layer.

Description

Technical Field

[0001] This invention relates to a high-value brown rice processing method, belonging to the field of grain deep processing technology. Background Technology

[0002] More than half of the world's population relies on rice as their staple food. Brown rice (caryopsis) is obtained after the rice grains have been hulled; it refers to the portion of the rice grain that is retained except for the husk. It is a complete fruit, similar in shape to a rice grain, generally long and slender or oval. Figure 1 As shown, brown rice consists of the pericarp, seed coat, nucellus, outer endosperm, endosperm, and embryo. The pericarp, seed coat, and nucellus are collectively called the cortex; the endosperm is the main part consumed by people and is also the most important component of rice. It can be divided into the outer endosperm (aleurone layer, sub-aleurone layer) and starch cells. Among them, the proteins in the cortex and intermediate layers fluoresce red-yellow after being stained with Rhodamine B; the aleurone cell walls fluoresce blue after being stained with fluorescent whitening agents; and the contents of aleurone cells and the starch in starch cells fluoresce green after being stained with FITC. Brown rice is milled to remove the cortex, outer endosperm, and embryo to obtain the commonly used polished rice.

[0003] However, the composition and nutrient distribution in the various structural layers of brown rice are extremely uneven: the pericarp mainly contains plant fiber, inositol phosphate, ash, etc., which are not easily digested and absorbed by the human body; the exocarp is composed of transversely arranged elongated thick-walled cells with wavy end walls. In mature brown rice, the thin-walled cells of the exocarp have died, and the tissue has collapsed into a sponge-like structure; the mesocarp is composed of several layers of transversely arranged elongated cells, with a loose and irregular structure; the endocarp has a layer of neatly arranged cells with thick cell walls, called transverse cells, and the layer of cells below the transverse cells elongates only longitudinally during the maturation process, becoming slender, called tubular cells; the seed coat contains a large amount of phytates and pigments, and has little nutritional value; the nucellus is aged nucellar tissue that adheres to the seed coat and is difficult to distinguish; its main components are plant fiber and phytates, etc. The seed coat and nucellus are high in phytic acid, which has a strong chelating ability with metal ions, making it difficult for the body to absorb trace elements such as calcium, iron, and zinc. In the outer endosperm, the aleurone layer cells are filled with aleurone grains, containing a large amount of proteinaceous aleurone grains, fat, vitamins, enzymes, and trace elements such as calcium, iron, zinc, potassium, selenium, and magnesium in the form of organic salts, which are easily absorbed by the body. The sub-aleurone layer, located just inside the aleurone layer, is somewhat similar in shape to aleurone cells and also contains a significant amount of protein and fat. The endosperm is composed of starch cells, which are larger than the aleurone layer cells, and their lumens are mainly filled with starch grains and a small amount of protein bodies. The closer to the interior of the endosperm, the larger the starch grains become. The embryo, located on the ventral stem, is oval-shaped and slightly sunken; its nutritional composition is similar to that of the aleurone layer, containing a significant amount of fat, protein, and vitamins.

[0004] Milling loss rate refers to the percentage reduction in the mass or volume of brown rice, and it is an indicator of the degree to which brown rice is milled. However, in modern rice processing, in order to increase storage stability, sensory characteristics, and eating quality to cater to the market, the industry commonly suffers from "over-milling," that is, pursuing excessive milling and increasing the milling loss rate. This not only increases processing losses but also causes the complete loss of nutrients in the rice bran and leads to problems such as an increased rate of broken rice. The national standard GB / T1354-2018, promulgated in 2019, formally proposed the definitions and judgment criteria for "refined milling" and "appropriate milling," emphasizing "moderate" processing. However, existing research suggests that the scope of "appropriate milling" is still relatively conservative and does not apply to the optimal milling reduction rate for specific varieties. In 2020, the Grain and Oil Nutrition Branch of the Chinese Cereals and Oils Association released the "White Paper on Rice Nutritional Loss Processing and Taste," stating that the domestic rice industry currently suffers from a serious problem of over-processing, wasting valuable grain resources and energy, which is detrimental to national food security and leads to many problems such as reduced rice taste and nutritional imbalance. In 2020, the Chinese Nutrition Society pointed out in the "Dietary Guidelines for Chinese Residents" that excessive processing of rice leads to a significant loss of dietary fiber and B vitamins.

[0005] Current processing technologies, besides milling, also include physical or biological methods to treat brown rice, improving its textural properties for direct consumption. Among physical methods, soaking softens the bran layer structure and shortens cooking time, but its drawbacks include a longer processing time and susceptibility to microbial contamination. Physical methods can be combined with pressure methods, using ultra-high pressure to disrupt the surface structure of brown rice, allowing water to penetrate more quickly under pressure and shortening processing time. However, this requires high precision and stability from the high-pressure equipment, making its widespread adoption in actual production difficult. Methods such as ultrasound, microwave, plasma, and infrared radiation create tiny pores on the surface of brown rice, facilitating water diffusion and starch gelatinization, reducing hardness. However, increasing power increases the damage to brown rice, and large-scale processing is relatively expensive. Furthermore, none of these methods address the antagonistic effect of phytic acid in the bran layer on the human body's mineral intake.

[0006] Biological methods, such as fermentation, germination, and enzymatic treatment, are relatively mild. Fermentation and germination utilize beneficial bacteria or enzymes produced by the rice's own metabolism to reduce the density of its structure. The addition of exogenous enzymes like cellulase and pectinase can also shorten cooking time and increase water absorption by approximately three times. Adding exogenous enzymes during the germination process, working synergistically with endogenous enzymes, results in a looser surface structure, a softer internal texture, and easier starch release during cooking, achieving a comprehensive improvement in both hardness and viscosity, effectively enhancing the quality characteristics of brown rice. The addition of phytase can also address the issue of phytic acid. However, besides being costly, biological methods are time-consuming, prone to microbial contamination, and require strict environmental conditions.

[0007] Furthermore, rice bran is a good source of low-allergenic protein, unsaturated fatty acids, dietary fiber, minerals, γ-aminobutyric acid (GABA), oryzanol, and polyphenols. Its antioxidant, hypoglycemic, and anti-tumor nutritional benefits have been extensively studied and confirmed. However, rice bran is prone to rancidity and unpleasant odors during processing and storage. Additionally, its poor palatability due to the outer layer makes it difficult to digest. Moreover, the high phytic acid content in the seed coat and nucellus can lead to mineral loss if ingested excessively. Therefore, rice bran is often used as animal feed or discarded, resulting in resource waste, environmental pollution, and hindering the sustainable development of agriculture and processing industries. Currently, the main application of rice bran is in the feed industry, with only 10%–15% of rice bran resources being fully utilized for extracting rice bran protein, rice bran oil, and rice bran dietary fiber; however, its utilization efficiency remains low.

[0008] Therefore, moderate processing of rice and efficient utilization of rice processing by-products are the future development trends of the rice processing industry, and also key directions for deeper and lower-carbon sustainable development of the entire rice industry chain. Summary of the Invention

[0009] In view of the defects and shortcomings of the existing technology, the present invention provides a high-value brown rice processing method, which can not only obtain high-quality polished rice, but also make high-value utilization of rice bran.

[0010] The purpose of this invention is to provide a high-value brown rice processing method, the method comprising the following steps:

[0011] (1) Perform multi-stage milling of brown rice

[0012] Brown rice is placed in a rice milling machine. The milling current and running time are adjusted to control the bran removal rate of 0.5-2.0% for each pass, and the bran removal rate reaches 20-25%. The rice and bran after each pass are collected separately, and the milling loss rate for each pass is calculated.

[0013] (2) Determine the optimal rolling reduction rate

[0014] Select brown rice and rice obtained from the odd-numbered or even-numbered milling process in step (1), and determine the bran retention rate, nutrient content, and quality characteristics respectively. Based on the comprehensive quality of bran retention rate, quality characteristics, and nutrient content, determine the optimal rice milling rate.

[0015] (3) Determine the stratified markers for each rice bran layer before the optimal milling reduction rate.

[0016] The metal element content, alkyl resorcinol content, and phytic acid content of rice bran before the optimal milling reduction rate were determined and significance analysis was performed. Based on the main enrichment areas of metal elements, alkyl resorcinol, and phytic acid, the layered structure and layer markers of rice bran were determined and divided into different structural layers.

[0017] (4) High-value utilization of rice bran

[0018] Based on the reduction rate corresponding to different structural layers determined in step (3), rice bran of different structural layers is collected for subsequent high-value utilization.

[0019] In one implementation, the bran removal rate in step (1) refers to the mass ratio of rice bran to the feed amount, and is calculated as follows:

[0020] i represents the number of channels.

[0021] In one implementation, the reduction rate in step (1) is calculated as follows:

[0022] i represents the number of channels.

[0023] In one embodiment, the nutrient content in step (2) includes protein content, fat content, starch content and ash content.

[0024] In one implementation, the quality characteristics described in step (2) include taste value, texture and gelatinization characteristics.

[0025] In one implementation, step (2) refers to the comprehensive quality based on bran retention, quality characteristics and nutrient content, specifically: selecting rice with a bran retention that meets the "suitable for milling" standard of the national standard GB / T 1354-2018, and with a nutrient content that tends to be stable and quality characteristics that are optimal.

[0026] In one embodiment, the metallic elements in step (3) include P, K, Mg, Ca, Fe, Al, Zn, Na, Cu, and Ni.

[0027] In one implementation, step (3) of determining the layered structure of rice bran is specifically based on the significant differences in the metal element content of each layer of rice bran, which is used to distinguish different biological structural layers, and the main enriched metal elements are marked as markers of the structural layer.

[0028] In one embodiment, the collection of rice bran with different structural layers in step (4) for subsequent high-value utilization can specifically be as follows: ① First milling to a milling loss rate of 2.06% to obtain exo-mesocarp bran, which can be used as feed raw material; ② Second milling to a milling loss rate of 7.40% to obtain endocarp-seed coat-nucleus bran rich in phytic acid, which can be used as raw material for making heavy metal adsorption particles; ③ Third milling to a milling loss rate of 13.64% to obtain aleurone bran, which can be used to make functional food additives or to extract high-quality rice bran protein, rice bran oil raw materials, etc.

[0029] In one embodiment, step (3) may also be: measuring the particle size of each rice bran before the optimal reduction rate, and determining different structural layers and corresponding reduction rates based on the particle size distribution.

[0030] In one embodiment, the particle size determination specifically involves using a Microtrac 3500 particle size analyzer to determine the particle size distribution of rice bran. The specific parameters are: suction type (0.25–2000 μm, dry method, reflection mode, particle shape set to irregular); each sample is measured 2–5 times, and the average value is taken; the particle size distribution data is obtained using the system's built-in software, and a particle size distribution map is plotted.

[0031] Another object of the present invention is to provide an application of the method described above in the field of brown rice processing.

[0032] The effective effects of this invention are as follows:

[0033] This invention provides a high-value-added brown rice grading and processing method that effectively solves the common problem of "over-milling" in current brown rice processing. Once the optimal milling reduction rate for a particular variety of brown rice is determined, it can be applied to the mass production of "suitable-milled rice" of that variety, reducing processing losses caused by excessive milling and lowering processing costs. Furthermore, it can guide the production of "suitable-milled rice" with higher and more balanced nutritional value, while maintaining better cooking properties and taste. Consuming "suitable-milled rice" as a staple food can avoid blood sugar problems caused by excessive consumption of refined rice and mineral loss caused by excessive consumption of brown rice. This invention also enables the high-value utilization of brown rice processing byproducts through grading and milling, maximizing the use of brown rice resources and increasing economic benefits. Finally, it provides a reference for subsequent research on grain grading and processing. Attached Figure Description

[0034] Figure 1 Fluorescence observation image of a complete brown rice slice;

[0035] Figure 2 This is a graph showing the changes in the appearance quality of rice with different husk retention rates after double-dyeing in Example 1.

[0036] Figure 3 A graph showing the trend of rice processing precision (husk retention rate) under different milling reduction rates;

[0037] Figure 4 The graph shows the trend of changes in the nutritional components of rice under different milling reduction rates; (A) is ash content; (B) is fat content; (C) is protein content; (D) is starch content.

[0038] Figure 5 Rice taste scores (appearance score, taste score, and overall score) are calculated for different milling reduction rates.

[0039] Figure 6 The textural properties (hardness, elasticity, and hardness / viscosity) of rice under different milling reduction rates;

[0040] Figure 7 The gelatinization characteristics (viscosity) of rice under different milling reduction rates;

[0041] Figure 8 Pearson correlation heatmap for nutritional quality and edible quality of rice under different milling reduction rates;

[0042] Figure 9 This is a particle size distribution diagram of rice bran under different milling reduction rates. Detailed Implementation

[0043] Measurement methods involved in the embodiments of the present invention

[0044] 1. Machining accuracy

[0045] The determination was performed using the eosin Y-methylene blue staining method as specified in GB / T 5502-2018 "Grain and Oil Inspection - Inspection of Rice Processing Precision".

[0046] (1) Preparation of staining solution: Prepare 500 ml each of 0.2 wt% eosin Y solution and methylene blue solution using 80% ethanol, then prepare the eosin Y-methylene blue staining stock solution at a 1:1 ratio. Store at room temperature and protected from light. The eosin Y-methylene blue staining solution is prepared by mixing 80% ethanol and eosin Y-methylene blue staining stock solution at a 1:1 ratio and should be prepared fresh before use.

[0047] (2) Staining: Select 10g of rice from each batch and... After cleaning the evaporating dish, add 15 ml of staining agent, shake well, let stand for 2 minutes, and then pour out the staining solution.

[0048] (3) Elution: Add 15ml of 80% ethanol, shake well and let stand for 1min, then elute three times.

[0049] (4) Measurement: The dyed and dried sample is placed in the JMJT-12 rice processing precision testing instrument, the image is collected, and the automatic calculation and analysis are performed to measure the peel retention degree. The average value of the two measurements is taken.

[0050] 2. Determination of protein content, fat content, starch content, and ash content

[0051] Take 500g of rice from each batch, grind it into rice flour, pass it through a 100-mesh sieve, seal it, and store it at -20℃ for later use.

[0052] (1) Protein content: The Kjeldahl method was used for determination according to GB 5009.5-2016 "National Food Safety Standard - Determination of Protein in Food". 1g of rice flour sample was placed in a digestion tube, and 0.2g of copper sulfate, 3g of potassium sulfate, and 10ml of sulfuric acid were added. The mixture was then digested in a digestion furnace. When the temperature in the digestion furnace reached 420℃, digestion continued for 1 hour. At this point, the liquid in the digestion tube was green and transparent. After cooling, 50ml of water was added, and the mixture was automatically added, distilled, titrated, and the titration data recorded using an automatic Kjeldahl nitrogen analyzer (prepared with sodium hydroxide solution, hydrochloric acid or sulfuric acid standard solution, and boric acid solution containing mixed indicator A or B). Finally, the protein content was calculated using the measured results.

[0053] (2) Fat content: The Soxhlet extraction method was used in accordance with GB 5009.6-2016 "National Food Safety Standard - Determination of Fat in Food". 2g of rice flour sample was placed in a filter paper tube, and defatted cotton soaked in ether was placed inside to prevent powder leakage. The filter paper tube was placed in the extraction tube of the Soxhlet extractor, and a receiving flask dried to constant weight was connected. Anhydrous ether or petroleum ether was added through the upper end of the extractor condenser to two-thirds of the flask's volume. The mixture was heated in a water bath, and the anhydrous ether or petroleum ether was continuously refluxed for extraction for 6 hours. Then, the receiving flask was removed, and the anhydrous ether or petroleum ether was recovered. When 1-2mL of solvent remained in the receiving flask, it was evaporated to dryness in a water bath, and then dried at 100℃±5℃ for 1 hour. After cooling in a desiccator for 0.5 hours, it was weighed. The above operation was repeated until constant weight was achieved (until the difference between two weighings did not exceed 2mg). Finally, the fat content was calculated using the measured results.

[0054] (3) Starch content: The determination was performed using the enzymatic hydrolysis method in GB 5009.9-2016 "National Food Safety Standard - Determination of Starch in Food". 2g of rice flour sample was placed in a funnel containing folded slow-speed filter paper. First, the fat was removed in five portions using 50mL of petroleum ether or diethyl ether. Then, soluble sugars were thoroughly washed away in portions using 100mL of 85% ethanol to ensure complete removal of any interfering soluble sugars. The ethanol was filtered off, and the residue was transferred to a 250mL beaker. The filter paper was washed with 50mL of water, and the washings were added to the beaker. The beaker was heated in a boiling water bath for 15 minutes to gelatinize the starch. The mixture was cooled to below 60℃, and 20mL of amylase solution was added. The mixture was kept at 55℃ for 1 hour with constant stirring. Then, one drop of this solution was added to one drop of iodine solution; no blue color should appear. If a blue color appeared, the mixture was heated again to gelatinize, and another 20mL of amylase solution was added. The mixture was kept at this temperature until the addition of iodine solution did not produce a blue color. Heat to boiling, cool, transfer to a 250 mL volumetric flask, add water to the mark, mix well, filter, and discard the initial filtrate. Take 50.00 mL of the filtrate, place it in a 250 mL Erlenmeyer flask, add 5 mL of hydrochloric acid (1+1), attach a reflux condenser, reflux in a boiling water bath for 1 h, cool, add 2 drops of methyl red indicator, neutralize to neutral with sodium hydroxide solution (200 g / L), transfer the solution to a 100 mL volumetric flask, wash the Erlenmeyer flask, add the washings to the 100 mL volumetric flask, add water to the mark, mix well, and set aside.

[0055] Pipette 5.00 mL of alkaline copper tartrate solution A and 5.00 mL of alkaline copper tartrate solution B (already standardized) into a 150 mL Erlenmeyer flask. Add 10 mL of water and two glass beads. Add the sample solution dropwise into the Erlenmeyer flask through a burette, heating to boiling within 2 minutes. Maintain the boiling state and continue titrating at a rate of one drop every two seconds until the blue color just fades. Record the volume of sample solution consumed. Perform the same procedure in triplicate and obtain the average volume consumed. Finally, calculate the starch content using the measured results.

[0056] (4) Ash content: Refer to GB 5009.4-2016 "National Food Safety Standard - Determination of Ash in Food" for the determination of total ash in food. Take 2g of rice flour sample into a quartz crucible or porcelain crucible. First, heat it on a hot plate with a small flame to fully carbonize the sample until there is no smoke. Then, place it in a high-temperature furnace and ignite it at 550℃±25℃ for 4 hours. Cool it to about 200℃, take it out, and place it in a desiccator to cool for 30 minutes. If carbon particles are found in the ignition residue before weighing, add a little water to the sample to moisten it and loosen the clumps. Evaporate the water and ignite it again until there are no carbon particles, indicating that the ash is complete before weighing. Repeat the ignition until the difference between the two weighings does not exceed 0.5mg to obtain constant weight. Finally, calculate the ash content using the measured results.

[0057] 3. Taste value, texture, and gelatinization characteristics

[0058] (1) Texture and taste value of cooked rice: First, referring to the preparation of small-batch rice samples in GB / T 15682-2008 "Sensory Evaluation Method for Cooking and Eating Quality of Rice and Grain in Grain and Oil Inspection", 10g of different types of rice were weighed into steaming dishes, washed quickly within 5 minutes, drained, and then soaked in 15ml of distilled water for 30 minutes. The rice was then steamed in a steamer for 20 minutes and then simmered for 10 minutes. After being air-dried and cooled outdoors for 100 minutes, the texture and taste value were measured using a TA-XT plus texture analyzer and a SATAKE STA1B rice taste meter.

[0059] (2) Gelatinization characteristics: Using a Swedish RVA TecMaster rapid viscosity meter, running Thermocline, program std1 (hold at 50℃ for 1 min, then at 12℃·min) was selected. -1 Rise to 95℃, maintain at 95℃ for 2.5 min, at a rate of 12℃·min -1 The temperature was lowered to 50°C and maintained at 50°C for 1.4 minutes. The stirrer was set to a speed of 960 r / min for the first 10 seconds. -1 Then maintain at 160 r·min -1 Add 3g of rice flour to a small aluminum cylinder containing 25.0ml of distilled water, and stir vigorously up and down 10 times with a small propeller to form a suspension; leave the propeller inside the cylinder, insert the aluminum cylinder into the RVA rotating tower, press the rotating tower, and start the test.

[0060] 4. Particle size determination method

[0061] Add 3g of rice flour to a beaker containing 25.0ml of distilled water and stir until a suspension is formed. The particle size distribution of the wheat bran was determined using a Microtrac 3500 particle size analyzer. Specific parameters were: suction type (0.02–2000μm, wet method, reflectance mode, particle shape set to irregular). Each sample was measured twice, and the average value was taken. Particle size distribution data were acquired using the system's built-in software, and a particle size distribution map was plotted.

[0062] 5. Phenolic acid composition and trace element determination

[0063] (1) Rice bran phenolic acid composition: Accurately weigh 20 mg of sample, hydrolyze it in the dark for 2 h in the presence of nitrogen using 10 mL of 2.0 mol / L NaOH, add 100 μL of 1 mg / mL 3,4,5-trimethoxycinnamic acid as an internal standard, neutralize the extract to pH 2 with 6 mol / L hydrochloric acid, and then extract twice with 3 times the volume of ethyl acetate. Combine the extracts, concentrate them, and dry them with nitrogen. Finally, redissolve the extract in 0.4 mL of 50% methanol solution, filter it through a 0.45 μm organic microfiltration membrane, and collect the filtrate for liquid chromatography analysis. Liquid chromatography conditions: C18 column (5 mm, 250 × 4.6 mm); detector: UV detector; detection wavelength: 320.8 nm; mobile phase A: acetonitrile; mobile phase B: acetate buffer solution at pH 4.6; injection rate: 0.8 mL / min; column temperature: 35 ℃; linear ratio of mobile phases A to B: 0–24 min, from 15 / 85 to 35 / 65; 24–24.5 min, from 35 / 65 to 60 / 40; 24.5–29 min, from 60 / 40 to 15 / 85; 29–34 min, maintain a 15 / 85 ratio for 5 min.

[0064] (2) Trace element composition of rice bran: The trace element composition of rice bran was determined by inductively coupled plasma mass spectrometry in GB 5009.268-2016 "National Food Safety Standard - Determination of Multiple Elements in Food". 0.5 g of rice bran sample was weighed into the inner container of the microwave digestion apparatus, 10 ml of nitric acid was added, the container was covered and left for 1 hour, the lid was tightened, and the digestion was carried out according to the standard operating procedure of the microwave digester (digestion conditions: 0-5 min, from 0℃ to 120℃; 5-10 min, constant temperature at 120℃; 10-15 min, from 120℃ to 150℃; 15-25 min, constant temperature at 150℃; 25-30 min, from 150℃ to 190℃; 30-50 min, constant temperature at 190℃). After cooling, remove the container, slowly open the lid to release the gas, rinse the inner lid with a small amount of water, place the digestion container on a temperature-controlled heating plate or in an ultrasonic water bath, heat at 100℃ for 30 min or ultrasonically degas for 2 min, dilute with water to 50 ml, mix well and set aside. Perform a blank test simultaneously. Use inductively coupled plasma mass spectrometry (ICP-MS) to determine trace elements in rice bran. (ICP-MS operating conditions: RF power 1500W; high-salt / concentric nebulizer; plasma gas flow rate 15 L / min; sampling cone / cutoff cone nickel / platinum; cone carrier gas flow rate 0.80 L / min; sampling depth 8–10 mm; auxiliary gas flow rate 0.40 L / min; peak jumping acquisition mode; helium flow rate 4–5 L / min; automatic detection mode; nebulizer temperature 2℃; 1–3 measurement points per peak; sample rise rate 0.3 r / s; 2–3 repetitions.)

[0065] 6. Alkyl resorcinol determination

[0066] The determination of alkylresorcinol was performed according to LS / T 3244-2015 "Whole Wheat Flour". 1 g of rice bran was weighed into a 50 ml centrifuge tube, 40 ml of ethyl acetate was added, and the mixture was extracted at room temperature with shaking for 48 h. After centrifugation at 3000 r / min for 10 min, the supernatant was transferred to a 50 ml centrifuge tube, dried under nitrogen, and reconstituted with 1 ml of ethyl acetate for later use. 10 μL of the supernatant was accurately transferred, 2 ml of diazonium salt working solution was added, and the mixture was incubated at room temperature in the dark for 1 h. The alkylresorcinol content was detected at a wavelength of 520 nm, and the content was calculated based on the working standard curve.

[0067] Example 1

[0068] A method for grading and processing high-value brown rice, the method comprising the following steps:

[0069] (1) Multi-stage milling of brown rice: 100 kg of fresh Yongyou 13 brown rice is milled in a Kumi Saino sand roller rice mill. The bran removal rate is precisely controlled by controlling the milling current and running time. i represents the number of passes; the first twelve passes are threshed at a 1% hulling rate; the last four passes are threshed at a 2% hulling rate, resulting in a reduction rate of... The rice bran and rice were removed to approximately 20% reduction. The bran and rice from each processing stage were collected separately, and the reduction rate for each stage was calculated, as shown in Table 1.

[0070] Table 1 Brown Rice Milling Parameters

[0071]

[0072] (2) Screening the optimal milling reduction rate of brown rice

[0073] Brown rice, two-stage rice, four-stage rice, six-stage rice, eight-stage rice, ten-stage rice, twelve-stage rice, fourteen-stage rice, sixteen-stage rice, eighteen-stage rice, and twenty-stage rice were selected. The processing precision (bain retention) of each rice stage under the corresponding reduction rate was measured. The results are as follows: Figure 2 (Eosin-methylene blue dye can stain the bran of brown rice blue and the germ layer purplish-red.) Figure 3 As shown, all twelve grades of rice met the national standard for "suitable for milling"; the nutritional components (including protein content, fat content, starch content, and ash content) were as follows. Figure 4 As shown, after twelve passes, the increase in starch content tends to level off, while the ash, protein, and fat contents still show a significant decrease; the quality (including taste value, texture, gelatinization characteristics, etc.) results are as follows. Figure 5 , 6 As shown in Figure 7, after twelve cooking times, the increase in taste score tends to level off; the texture of the 12-cooked rice is optimal (the increase in elasticity tends to level off; hardness and hardness / viscosity tend to be minimal); the gelatinization characteristics are excellent after ten cooking times; Figure 8It can be seen that the nutritional quality and edible quality of this rice variety are basically related. Therefore, among the rice varieties selected with a 2% bran removal rate, the 12th-grade rice has the highest overall quality, and the optimal milling reduction rate for this rice variety is determined to be 13.64%.

[0074] (3) Determine the stratification markers for each rice bran layer before the optimal reduction rate.

[0075] The metal element content, alkyl resorcinol content, and phytic acid content of each rice bran were determined and significance analysis was performed. Based on the main enrichment areas of metal elements, alkyl resorcinol, and phytic acid, the layered structure of the rice bran was determined. The results are shown in Table 2.

[0076] Table 2. Trace elements and contents of alkyl resorcinol and phytic acid in rice bran with different milling reduction rates.

[0077]

[0078]

[0079] Note: Each lowercase letter indicates a significant difference (p < 0.05) between different samples.

[0080] Table 2 shows that the differences in metal element content between the first and second milling processes are all significant, indicating that the two processes belong to different structural layers. Rice bran is milled from the outside in with a 1% reduction rate. Based on the structure of brown rice, the first milling process determines that the rice bran belongs to the outer layer, i.e., the outer bran. Al is mainly enriched in the first milling process and can be used as a marker for the outer bran. The metal element content between the second and third milling processes is mostly significantly different, indicating that the second milling process belongs to the mesocarp layer. Fe is enriched in the second milling process and can be used as a marker for the mesocarp layer. The differences in metal element content between the third and fourth milling processes are not significant, and the fourth and... The fifth layer of rice bran showed a significant difference in metal content, therefore the third and fourth layers can be identified as the endocarp layer. Alkyl resorcinol is mainly distributed in the third and fourth layers of rice bran, and is therefore identified as a marker of the endocarp layer. The fifth and sixth layers of rice bran showed no significant difference in metal content, while the sixth and seventh layers showed a significant difference. Therefore, the fifth and sixth layers can be identified as the seed coat and nucellus layers, and Mg is mainly enriched in these two layers, which can be used as markers of the seed coat-nucellus layer. The last six layers can be identified as the aleurone layer, and Cu can be used as its marker. By dividing the rice bran into layers based on the above markers, the biological structural layer to which each layer of rice bran belongs can be obtained.

[0081] (4) High-value utilization of rice bran

[0082] Based on the milling reduction rate corresponding to different structural layers in step (3), different rice bran can be collected to facilitate subsequent high-value utilization. For example, it can be milled through three milling processes: ① First milling to a milling reduction rate of 2.06% to obtain exo-mesocarp bran, which can be used as feed raw material; ② Second milling to a milling reduction rate of 7.40% to obtain endocarp-seed coat-nucleus bran rich in phytic acid, which can be used as raw material for making heavy metal adsorption particles; ③ Third milling to a milling reduction rate of 13.64% to obtain aleurone bran, which can be used to make functional food additives or to extract high-quality rice bran protein, rice bran oil raw materials, etc.

[0083] Example 2

[0084] (1) Same as step (1) in Example 1;

[0085] (2) Same as step (1) in Example 1;

[0086] (3) Particle size was measured for each rice bran before the optimal reduction rate, and the results are as follows: Figure 9 As shown, the phenomenon of multiple peaks in particle size during the grinding process is due to the different mechanical properties of different structural layers of brown rice. The outer layer and the middle layer are loosely bonded and easily detach and separate. The energy required to pulverize them is only 1 / 4 of the energy required to break the middle layer and the aleurone layer, making them easy to pulverize into small particles. For example, in the first and second grinding processes, it is obvious that the peak at 30μm of the rice bran particle size disappears and the peak at 160μm becomes larger, indicating that the outer layer has detached; that is, the rice bran in the first grinding mainly belongs to the outer layer. From the seventh grinding process onwards, obvious peaks of 4μm and 10μm appear, indicating that these have begun to grind out aleurone particles that are clustered within the cells of the aleurone layer; therefore, the seventh grinding process onwards belongs to the aleurone layer.

[0087] (4) According to step (3), the rice bran is divided into three layers: the outer layer bran, with a corresponding milling loss rate of 0 to 0.97%, which can be used as feed raw material; the middle layer bran, with a corresponding milling loss rate of 0.97 to 7.40%, which can be used as raw material for making heavy metal adsorption granules; and the aleurone layer bran, with a corresponding milling loss rate of 7.40 to 13.64%, which can be used to make functional food additives or to extract high-quality rice bran protein, rice bran oil raw materials, etc.

[0088] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A processing method for high-value brown rice, characterized in that, The method includes the following steps: (1) Perform multiple grading and milling processes on brown rice. Brown rice is placed in a rice milling machine. The milling current and running time of the rice milling machine are adjusted to control the bran removal rate of 0.5-2.0% for each pass, and the bran removal rate reaches 20-25%. The rice and the corresponding bran after each pass are collected separately, and the milling loss rate of each pass is calculated. (2) Determine the optimal rolling reduction rate Brown rice and rice obtained in step (1) with an odd number of milling passes or an even number of milling passes were selected, and the degree of bran retention, nutrient content and quality characteristics were measured respectively. Based on the comprehensive quality of the degree of bran retention, quality characteristics and nutrient content, the optimal milling reduction rate was determined. (3) Determine the stratified markers for each rice bran before the optimal milling reduction rate. The metal element content, alkyl resorcinol content, and phytic acid content of rice bran before the optimal milling reduction rate were determined and significance analysis was performed. Based on the main enrichment areas of metal elements, alkyl resorcinol, and phytic acid content, the layered structure and layer markers of rice bran were determined and divided into different structural layers. (4) High-value utilization of rice bran Based on the reduction rate corresponding to different structural layers determined in step (3), rice bran of different structural layers is collected for subsequent high-value utilization.

2. The method according to claim 1, characterized in that, The nutrient content mentioned in step (2) includes protein content, fat content, starch content and ash content.

3. The method according to claim 1, characterized in that, The quality characteristics mentioned in step (2) include taste value, texture and gelatinization characteristics.

4. The method according to claim 1, characterized in that, The comprehensive quality based on husk retention, quality characteristics and nutrient content mentioned in step (2) specifically refers to selecting rice that meets the "suitable for milling" standard of the national standard GB / T 1354-2018, has a husk retention that is relatively stable, and has the best quality characteristics.

5. The method according to claim 1, characterized in that, The metallic elements mentioned in step (3) include K, Mg, Ca, Fe, Al, Zn, Na, Cu and Ni.

6. The method according to claim 1, characterized in that, Step (3) describes determining the layered structure of rice bran by distinguishing different biological structural layers based on the significant differences in the metal element content of each layer of rice bran, and marking the main enriched metal elements as markers of the structural layer.

7. The method according to claim 1, characterized in that, Step (4) of collecting rice bran with different structural layers for subsequent high-value utilization specifically involves: The product is milled to a reduction rate of 2.06% to obtain pericarp bran, which is used as a feed ingredient. Two milling processes were performed to reduce the milling rate to 7.40%, yielding endocarp-seed coat-nucellus bran rich in phytic acid, which was used as a raw material for making heavy metal adsorption particles. The product is milled three times until the milling loss is 13.64%, resulting in aleurone bran, which can be used to make functional food additives, extract high-quality rice bran protein, or as a raw material for rice bran oil.

8. The method according to claim 1, characterized in that, The calculation method for the reduction rate in step (1) is as follows: ; i represents the number of channels.

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