A method for preparing rice bran oil by coupling rice bran expansion and solid state fermentation

Abstract

The application discloses a method for preparing rice bran oil through puffing and solid-state fermentation of rice bran, and belongs to the technical field of grain and oil processing. The method comprises the following steps: (1) removing impurities from the rice bran, and controlling the initial moisture content to be 8.0%-10.0%; (2) wet puffing to obtain puffed rice bran; (3) inoculating a compound microbial inoculum composed of bacillus subtilis and lactobacillus plantarum to perform solid-state fermentation, and obtaining fermented rice bran; (4) low-temperature drying to obtain fermented modified rice bran; and (5) oil extraction to obtain rice bran oil. Through the segmented coupling process of puffing and solid-state fermentation, the physical wall breaking and biological upgrading are progressively and cooperatively performed, on the basis of inactivating endogenous enzymes and improving storage stability, the compound microbial inoculum is used for targeted degradation of fiber-wrapped tissues, and a mild and weak acidic environment is used for inhibiting oxidative degradation of heat-sensitive active ingredients, so that the rice bran oil extraction rate and the content of gamma-oryzanol are simultaneously improved, and the method is suitable for industrialized production of high-quality functional rice bran oil.

Description

Technical Field

[0001] This invention relates to the field of grain and oil processing technology, and in particular to a method for preparing rice bran oil by coupled solid-state fermentation with rice bran puffing, so as to improve the extraction rate and γ-oryzanol content of rice bran oil. Background Technology

[0002] Rice bran is a major byproduct of rice processing, rich in unsaturated fatty acids, γ-oryzanol, tocopherol, phytosterols, and other functional active ingredients, making it a high-quality raw material for preparing premium edible oils. However, fresh rice bran has extremely high activity of endogenous lipases and lipoxygenases, making it highly susceptible to hydrolysis and oxidative rancidity under normal temperature storage conditions. This leads to a rapid increase in acid value and quality deterioration, making it unsuitable for long-term storage and delayed processing. Therefore, the industry commonly employs extrusion puffing technology for instantaneous high-temperature enzyme inactivation and stabilization of fresh rice bran, which is currently the only rice bran pretreatment method that can be applied on a large scale.

[0003] The single puffing and stabilization process has inherent technical defects, which restricts the improvement of quality and efficiency in the rice bran oil production industry. Pure physical puffing relies solely on mechanical extrusion and instantaneous pressure relief to loosen the material and inactivate enzymes. It can only destroy the surface structure of rice bran, but cannot completely break the dense cellulose and hemicellulose interwoven network inside. A large amount of oil is encapsulated inside the solid fiber matrix, making it difficult to fully extract in subsequent solvent leaching. This results in low oil yield and high residual oil in the leached meal in industrial production. At the same time, the high temperature and high pressure conditions of puffing cause a large amount of heat-sensitive γ-oryzanol in rice bran to undergo thermal degradation and oxidative loss. The finished rice bran oil has low oryzanol content, weak functionality, serious product homogenization, and lack of competitiveness in the high-end market. In addition, the single physical processing method cannot change the encapsulation characteristics of bound oil in rice bran, nor can it achieve the targeted retention and enrichment of functional active ingredients, resulting in low added value of processed products.

[0004] To improve the oil yield and enrich functional components in rice bran oil extraction, existing research has attempted to modify rice bran through microbial fermentation. However, most existing microbial fermentation modification schemes directly ferment virgin rice bran. Due to the high enzyme activity and susceptibility to rancidity and mold growth in virgin rice bran, the raw material stability is poor in the early stages of fermentation. Furthermore, there are issues such as high risk of contamination by other microorganisms in the fermentation system, uncontrollable fermentation cycle, and poor batch stability, making them unsuitable for continuous industrial production. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the oil extraction rate is low, the loss of functional components such as γ-oryzanol is large, and the process stability is poor in the existing rice bran oil production process. The present invention provides a method for preparing rice bran oil by rice bran puffing coupled with solid-state fermentation, and provides the rice bran oil obtained by the method.

[0006] To address the above problems, the present invention proposes the following technical solution: In a first aspect, the present invention provides a method for preparing rice bran oil by coupled solid-state fermentation of rice bran puffing, comprising the following steps: (1) removing impurities from rice bran and controlling the initial moisture content of rice bran to be 8.0% to 10.0% to obtain purified rice bran; (2) performing wet puffing on the purified rice bran to obtain puffed rice bran; (3) inoculating the puffed rice bran with a compound microbial agent for solid-state fermentation to obtain fermented rice bran; wherein the compound microbial agent includes Bacillus subtilis and Lactobacillus plantarum; (4) drying the fermented rice bran to obtain fermented modified rice bran; and (5) extracting the fermented modified rice bran to obtain rice bran oil.

[0007] Preferably, in step (2), saturated steam is first introduced to condition the purified rice bran, followed by extrusion and puffing. After puffing, the temperature is lowered to 35-45°C to obtain puffed rice bran. The pressure of the saturated steam is 0.12-0.18 MPa, the conditioning temperature is 65-75°C, the moisture content of the rice bran after conditioning is 11%-13%, and the conditioning time is 3-5 min.

[0008] Preferably, the material temperature during extrusion puffing is 110–125°C, and the die pressure is 3–8 MPa.

[0009] Preferably, in step (3), the mass ratio of Bacillus subtilis powder to Lactobacillus plantarum powder in the compound microbial agent is 1:1 to 1:1.5; the viable count of the compound microbial agent is not less than 10. 9 The CFU / g, based on the total mass of the compound microbial agent, is added at a rate of 0.2% to 0.5% of the dry weight of the puffed rice bran.

[0010] Preferably, in step (3), the moisture content of the puffed rice bran is adjusted to 18% to 22%, and fermented at 28 to 32°C for 24 to 36 hours; the oxygen volume concentration in the gas phase of the fermentation container is controlled to be 8% to 12%, the carbon dioxide volume concentration is 5% to 8%, and the aeration rate is 0.15 to 0.25 L of sterile air per kilogram of dry weight of puffed rice bran per hour.

[0011] Preferably, in step (4), the material temperature does not exceed 55°C during drying, and the material moisture content is dried to 8.0% to 9.0%.

[0012] Preferably, in step (5), food-grade n-hexane is used as the leaching solvent, the leaching temperature is 50-55°C, and the leaching time is 90-120 min.

[0013] Secondly, the present invention also provides rice bran oil, which is prepared by the method described in any of the above-mentioned methods.

[0014] Compared with the prior art, the technical effects achieved by the present invention include: This invention provides a method for preparing rice bran oil through rice bran puffing coupled with solid-state fermentation, employing a segmented coupled process of wet puffing followed by solid-state fermentation. Wet puffing inactivates endogenous lipases and lipoxygenases, while simultaneously loosening the material and forming a porous network structure, providing a structural substrate for the attachment of fermentation agents and enzyme metabolism. In solid-state fermentation, a composite agent composed of Bacillus subtilis and Lactobacillus plantarum is used to target and degrade the dense cellulose and hemicellulose encapsulation in rice bran, dissociating the bound oil into easily extractable free oil. Simultaneously, the mild, weakly acidic environment created during fermentation inhibits the oxidative degradation of heat-sensitive active ingredients such as γ-oryzanol. This invention utilizes the synergistic effect of puffing and solid-state fermentation steps to simultaneously increase oil extraction rate and γ-oryzanol content, thus solving the technical problems of low oil yield and significant loss of functional components in traditional single puffing processes, as well as the poor stability and difficulty in mass production of direct fermentation processes. This method is suitable for the efficient resource utilization and high-value utilization of rice bran.

[0015] The rice bran oil provided by this invention is produced by the above process. It has sufficient oil extraction, low residual oil in the meal, and functional active ingredients such as γ-oryzanol and vitamin E are selectively retained and enriched during the processing, thus having high functional nutritional value and storage stability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a method for preparing rice bran oil by coupled solid-state fermentation of rice bran, provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Similar component reference numerals in the drawings represent similar components. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0020] It should also be understood that the terminology used in the specification of embodiments of the present invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the present invention. As used in the specification of embodiments of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" are intended to include the plural forms.

[0021] Rice bran is a major byproduct of rice processing, rich in unsaturated fatty acids, γ-oryzanol, tocopherol, and other active ingredients. However, fresh rice bran has high endogenous enzyme activity and is prone to rancidity. Traditional single-stage puffing processes suffer from low oil yield and significant oryzanol loss, while direct fermentation processes have poor stability and are difficult to mass-produce. To address these issues, this invention provides a method for preparing rice bran oil through rice bran puffing coupled with solid-state fermentation. First, the rice bran is wet-puffed to inactivate enzymes, stabilize it, and physically loosen and break down cell walls. Then, solid-state fermentation with a compound microbial agent is used for biological modification and quality improvement, simultaneously increasing both oil extraction rate and oryzanol content. A flowchart of this method is shown below. Figure 1 .

[0022] Specifically, the method of the present invention includes the following steps: (1) Remove impurities from rice bran and control the initial moisture content of rice bran to 8.0% to 10.0% to obtain purified rice bran; (2) The purified rice bran is subjected to wet puffing to obtain puffed rice bran; (3) Inoculate the puffed rice bran with a compound microbial agent and carry out solid-state fermentation to obtain fermented rice bran; (4) The fermented rice bran is dried to obtain fermented modified rice bran; (5) The fermented modified rice bran is extracted to obtain rice bran oil.

[0023] The following provides a detailed explanation of each step.

[0024] In step (1), rice bran obtained from fresh rice processing is selected and subjected to a combination of vibrating sieving and magnetic separation to remove mechanical impurities such as broken rice, bran flakes, straw, mud, sand, and iron filings. Moldy and clump-forming materials are also removed to ensure the purity and processing stability of the fermentation substrate. After impurity removal, the initial moisture content of the rice bran is controlled at 8.0% to 10.0%, for example, 8.0%, 8.5%, 9.0%, 9.5%, and 10.0%. Too low an initial moisture content will make it difficult for the rice bran to absorb water evenly during subsequent puffing and conditioning, resulting in uneven material plasticity. Too high an initial moisture content will exacerbate the enzymatic rancidity of the raw material during storage and waiting for processing, both of which are detrimental to the stable progress of subsequent puffing and fermentation processes. After impurity removal and initial moisture control, the rice bran material is uniformly loose, providing a clean and stable raw material for subsequent wet puffing.

[0025] In step (2), the wet puffing step is as follows: the purified rice bran is sent into the puffing conditioning system, saturated steam is first introduced for conditioning treatment, and then it is sent into the twin-screw extruder for extrusion puffing.

[0026] During the conditioning process, saturated steam with an absolute pressure of 0.12–0.18 MPa (corresponding to a saturated steam temperature of approximately 105–118℃) is introduced. By adjusting the steam flow rate, the temperature of the rice bran after conditioning is controlled at 65–75℃, the moisture content of the rice bran after conditioning is 11%–13%, and the conditioning time is 3–5 minutes. This ensures uniform moisture penetration and consistent plasticity within the rice bran. If the conditioning temperature is too low, the steam will not be able to fully penetrate the rice bran; if the conditioning temperature is too high, starch gelatinization and early loss of oryzanol will easily occur. If the conditioning time is too short, the moisture distribution will be uneven; if it is too long, energy consumption will increase.

[0027] During extrusion puffing, the material temperature in the puffer is controlled at 110–125℃, for example, 110℃, 115℃, or 125℃. The die pressure is 3–8 MPa, for example, 3 MPa, 5 MPa, or 8 MPa. The screw speed is 180–220 r / min, for example, 180 r / min, 200 r / min, or 220 r / min, ensuring an effective residence time of 15–25 s for the material within the machine. Through the synergistic effect of instantaneous high temperature and pressure, mechanical shearing, and controllable residence time, the endogenous lipases and oxidases in rice bran are completely inactivated. It is important to note that the screw speed directly determines the mechanical shearing intensity and the degree of material puffing: if the speed is too low, there will be insufficient shearing, resulting in a dense rice bran structure with low porosity, which is not conducive to the subsequent penetration of fermentation agents and oil dissociation; if the speed is too high, the material will be excessively sheared, resulting in overly fine particles, which can easily cause material caking and reduced air permeability, which is not conducive to the construction of a microaerobic fermentation environment. The material residence time is matched with the temperature and pressure conditions. Within this parameter range, the inactivation rate of endogenous enzymes in rice bran can reach over 99.5%. At the same time, the material forms a uniform porous network structure with a porosity of 42% to 48%, completing the enzyme inactivation stabilization and physical loosening and cell wall breaking of rice bran. This provides an excellent structural substrate basis for subsequent solid-state fermentation microbial community attachment, enzymatic cell wall breaking, and oil dissolution.

[0028] After puffing and discharge, the material is cooled to 35–45°C, such as 35°C, 40°C, or 45°C, to eliminate residual heat and prevent high-temperature residue from affecting the activity of the microbial community in subsequent solid-state fermentation. Cooling methods can include natural air cooling, but are not limited to it; forced ventilation cooling, fluidized bed cooling, and other conventional cooling methods in this field can also be used. Through wet puffing, endogenous lipases and lipoxygenases in rice bran can be completely inactivated, fundamentally solving the problem of rancidity during subsequent storage of rice bran. Simultaneously, the physical loosening and cell wall breaking of the rice bran is completed, forming a porous network structure.

[0029] In step (3), specifically, the solid-state fermentation step of the present invention involves inoculating puffed rice bran with a compound microbial agent for solid-state fermentation to obtain fermented rice bran. The compound microbial agent includes Bacillus subtilis and Lactobacillus plantarum, and the two microbial agents complement each other and synergistically enhance each other's effects during the fermentation process.

[0030] In the compound microbial agent, the mass ratio of Bacillus subtilis powder to Lactobacillus plantarum powder is 1:1 to 1:1.5, for example, 1:1, 1:1.2, or 1:1.5. The viable count of the compound microbial agent is not less than 10. 9 CFU / g; the addition amount, based on the total mass of the compound microbial agent, is 0.2%–0.5% of the dry weight of the puffed rice bran, for example, 0.2%, 0.4%, or 0.5%. Too low an addition amount will result in insufficient enzyme production and incomplete fiber degradation, leading to poor oil release; too high an addition amount will cause an imbalance in the microbial community structure, with excessive microbial metabolism consuming some small-molecule nutrients, thus reducing oil extraction efficiency. The compound microbial agent should be evenly inoculated into the puffed rice bran and thoroughly mixed to ensure uniform adhesion and no localized accumulation of the agent.

[0031] The moisture content of the material is adjusted to 18%–22% using sterile water, for example, 18%, 20%, or 22%. Too low a moisture content hinders bacterial growth and extracellular enzyme diffusion, while too high a moisture content reduces permeability and promotes the growth of unwanted microorganisms. The mixed material is then placed under constant temperature and sealed conditions and fermented at 28–32°C for 24–36 hours. Too low a fermentation temperature slows down bacterial metabolism and prolongs the fermentation cycle, while too high a temperature inhibits bacterial activity or even causes bacterial inactivation. The oxygen volume concentration in the gas phase of the fermentation container is 8%–12%, and the carbon dioxide volume concentration is 5%–8%. The aeration rate is 0.15–0.25 L of sterile air per kilogram of dry puffed rice bran per hour. This micro-oxygen gas environment meets the trace oxygen requirements for Bacillus subtilis enzyme production and metabolism, while also being compatible with the weakly acidic anaerobic growth characteristics of Lactobacillus plantarum, avoiding oxidation of active ingredients caused by excessive oxygen and ensuring stable synergistic metabolism of the complex microbial community.

[0032] During solid-state fermentation, the complex microbial community produces extracellular enzymes such as cellulase and hemicellulase, which target and degrade the rice bran fiber-encapsulated structure, releasing bound oils and providing a structural basis for subsequent leaching and oil extraction. At the same time, the mild and weakly acidic environment formed by the fermentation system can effectively inhibit the oxidative degradation of γ-oryzanol, achieving the targeted retention and enrichment of functional components.

[0033] In step (4), specifically, the drying step of this invention involves sending the fermented rice bran into a low-temperature hot air drying device after solid-state fermentation, strictly controlling the material temperature to not exceed 55°C, and continuously drying until the material moisture content is 8.0%–9.0%, then naturally cooling to room temperature. A drying temperature exceeding 55°C will cause thermal degradation and loss of heat-sensitive active ingredients such as γ-oryzanol and vitamin E; excessively high final moisture content will hinder the penetration of subsequent leaching solvents and oil dissolution, while excessively low moisture content will lead to over-drying and increased energy consumption. After drying, fermented modified rice bran with a loose structure, high oil freeness, and rich oryzanol content is obtained for leaching.

[0034] In step (5), specifically, the leaching oil extraction step of this invention involves feeding fermented modified rice bran into an industrial continuous leaching production line, using food-grade n-hexane as the leaching solvent, a leaching temperature of 50–55°C, and a leaching time of 90–120 minutes to ensure complete oil extraction. If the leaching temperature is too low, the leaching rate will be slow and the oil yield will be low; if the temperature is too high, solvent loss will be significant and some active ingredients may be damaged. If the leaching time is too short, the leaching will be insufficient; if the time is too long, energy consumption and solvent consumption will increase. The mixed oil obtained from leaching is then subjected to negative pressure evaporation and solvent removal treatment to obtain crude rice bran oil. The crude rice bran oil can be further refined through conventional refining processes such as degumming, deacidification, decolorization, and deodorization to obtain rice bran oil.

[0035] In summary, this invention first achieves enzyme inactivation and stabilization of rice bran and physical loosening and cell wall breaking through wet puffing, and then achieves targeted degradation of fiber structure and dissociation of bound oil through solid-state fermentation with compound microbial agents. The physical cell wall breaking and biological quality improvement are connected and synergistically enhanced. Combined with low-temperature drying and leaching oil extraction, the invention ultimately achieves a simultaneous increase in rice bran oil extraction rate and γ-oryzanol content.

[0036] The effectiveness of the method for preparing rice bran oil by rice bran puffing coupled with solid-state fermentation provided by the present invention is verified through the following examples / comparative examples.

[0037] Experimental materials: Fresh rice bran (initial moisture content 9.2%); Bacillus subtilis powder, with an effective viable count ≥102 9 CFU / g; Lactobacillus plantarum bacterial powder, with an effective live bacteria count ≥10. 9 CFU / g; food-grade n-hexane.

[0038] Main equipment: twin-screw extruder; constant temperature sealed solid fermentation tank; low temperature hot air drying equipment; industrial continuous leaching production line; high performance liquid chromatograph (equipped with ultraviolet detector and fluorescence detector); Soxhlet extraction device.

[0039] Example 1 A method for preparing rice bran oil by coupled solid-state fermentation with rice bran puffing includes: (1) Raw material purification: Fresh rice bran is taken and mechanical impurities such as broken rice, straw, mud, sand, and iron filings are removed by sieving and magnetic separation. Moldy and lumpy materials are removed. The initial moisture content of the raw material is 9.2%.

[0040] (2) Steam conditioning: The purified rice bran is conditioned by passing saturated steam with an absolute pressure of 0.12 to 0.18 MPa. The temperature of the rice bran after conditioning is controlled at 70℃, the moisture content is 12%, and the conditioning time is 4 min, so that the moisture penetration of the material is uniform and the plasticity is consistent.

[0041] (3) Extrusion puffing: The conditioned rice bran is fed into a twin-screw extruder, and the material temperature is controlled at 118℃, the die pressure at 5MPa, and the screw speed at 200 r / min. Through instantaneous high temperature and high pressure, the endogenous enzymes in the rice bran are completely inactivated and the cell walls are physically loosened and broken.

[0042] (4) Air cooling: After puffing and discharging, the material is cooled to 40°C by natural air cooling to eliminate residual heat and avoid high temperature residue affecting the activity of subsequent solid-state fermentation microorganisms.

[0043] (5) Solid-state fermentation: Inoculate puffed rice bran with a single Bacillus subtilis powder, with a viable count of ≥10. 9 The amount of CFU / g added is 0.3% of the dry weight of the puffed rice bran; the moisture content of the material is adjusted to 20% with sterile water, and solid fermentation is carried out at 30℃ under a constant temperature, closed micro-aerobic conditions for 30 h.

[0044] (6) Low temperature drying: The fermented material is dried with hot air at 52°C until the moisture content is 8.5%.

[0045] (7) Solvent leaching: food-grade n-hexane was used as solvent, leaching temperature was 52℃ and leaching time was 105 min.

[0046] (8) Desolventizing and refining: The mixed oil obtained by leaching is desolventized by negative pressure evaporation, and the crude oil is refined by degumming, deacidification, decolorization and deodorization processes to obtain rice bran oil.

[0047] Example 2 This embodiment is the same as embodiment 1, except that in step (5), a single Lactobacillus plantarum powder is used instead of Bacillus subtilis powder, while the other process conditions remain unchanged.

[0048] Example 3 This embodiment is the same as Embodiment 1, except that in step (5), a compound bacterial agent of Bacillus subtilis and Lactobacillus plantarum is used, with a mass ratio of 1:1.2, and the viable count of the bacterial agent is ≥10. 9The amount of CFU / g added is 0.3% of the dry weight of the puffed rice bran; the moisture content of the material is adjusted to 20% with sterile water, and solid-state fermentation is carried out at a constant temperature of 30℃ for 30 h; the other process conditions remain unchanged.

[0049] Example 4 This embodiment is the same as Embodiment 3, except that: the mass ratio of Bacillus subtilis to Lactobacillus plantarum in the compound microbial agent is 1:0.9, and the total amount of microbial agent added is 0.15% of the dry weight of puffed rice bran; the other process conditions remain unchanged.

[0050] Example 5 This embodiment is the same as Embodiment 3, except that: the mass ratio of Bacillus subtilis to Lactobacillus plantarum in the compound microbial agent is 1:1.6, and the total amount of microbial agent added is 0.6% of the dry weight of puffed rice bran; the other process conditions remain unchanged.

[0051] Comparative Example 1 This comparative example represents the baseline process without solid-state fermentation, as detailed below: (1) Raw material purification: Fresh rice bran is taken and mechanical impurities such as broken rice, straw, mud, sand, and iron filings are removed by sieving and magnetic separation. Moldy and lumpy materials are removed. The initial moisture content of the raw material is 9.2%.

[0052] (2) Steam conditioning: The purified rice bran is conditioned by passing saturated steam with an absolute pressure of 0.12 to 0.18 MPa. The temperature of the rice bran after conditioning is controlled at 70℃, the moisture content is 12%, and the conditioning time is 4 min, so that the moisture penetration of the material is uniform and the plasticity is consistent.

[0053] (3) Extrusion puffing: The conditioned rice bran is fed into a twin-screw extruder, and the material temperature is controlled at 118℃, the die pressure at 5MPa, and the screw speed at 200 r / min. Through instantaneous high temperature and high pressure, the endogenous enzymes in the rice bran are completely inactivated and the cell walls are physically loosened and broken.

[0054] (4) Air cooling: After the puffed material is discharged, it is cooled to 40°C by natural air cooling to eliminate residual heat and avoid the adverse effects of high temperature on the quality of the material.

[0055] (5) Low temperature drying: The cooled puffed rice bran is dried with hot air at 52°C to a moisture content of 8.5% to obtain dried puffed rice bran.

[0056] (6) Solvent leaching: food-grade n-hexane was used as solvent, leaching temperature was 52℃ and leaching time was 105 min.

[0057] (7) Desolventizing and refining: The mixed oil obtained by leaching is desolventized by negative pressure evaporation, and the crude oil is refined by degumming, deacidification, decolorization and deodorization processes to obtain rice bran oil.

[0058] Comparative Example 2 The only difference between this comparative example and the compound microbial agent fermentation process in Example 3 is that the steam conditioning and extrusion puffing processes are omitted. Specifically, after purification, the moisture content of fresh rice bran is directly adjusted to 20% with sterile water, and then inoculated with a compound microbial agent (Bacillus subtilis and Lactobacillus plantarum in a mass ratio of 1:1.2, with an addition amount of 0.3% of the dry weight of the rice bran). Fermentation is carried out at a constant temperature of 30°C in a sealed, microaerobic environment for 30 hours. Subsequent drying, leaching, and refining are the same as in Example 3.

[0059] Comparative Example 3 The only difference between this comparative example and the compound microbial agent fermentation process in Example 3 is the change in the order of the steps: fermentation first, followed by puffing. Specifically, after the fresh rice bran is purified, the moisture content of the material is adjusted to 20% with sterile water, and then inoculated with a compound microbial agent (Bacillus subtilis and Lactobacillus plantarum in a mass ratio of 1:1.2, with an addition amount of 0.3% of the dry weight of the rice bran). The mixture is then fermented at a constant temperature of 30°C in a closed microaerobic environment for 30 hours. After fermentation, the mixture is fed into a twin-screw extruder, where the material temperature is 118°C, the die pressure is 5 MPa, and the screw speed is 200 r / min for extrusion and puffing. After air cooling, the mixture is dried, extracted, and refined to obtain rice bran oil.

[0060] Performance testing The rice bran oil and extracted meal obtained from the above examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1.

[0061] (1) Rice bran oil extraction rate: Based on the total oil content of the pretreated rice bran raw material, the crude fat content of the raw material was determined by Soxhlet extraction; the actual crude oil obtained by extraction was weighed, and the extraction rate was calculated according to the following formula: Leaching rate = (actual crude oil mass extracted ÷ total oil mass of raw materials) × 100%.

[0062] (2) Residual oil content in the meal: According to GB / T 10359-2008 "Determination of oil content in oilseed cake", the residual oil content of rice bran meal after leaching was determined by Soxhlet extraction. After drying and removing water, the sample was extracted by reflux with petroleum ether. The mass of the extracted oil was weighed and the residual oil content of the meal was calculated.

[0063] (3) γ-Oryzanol content: determined according to LS / T 6121-2017 "Determination of γ-Oryzanol in Vegetable Oils by High Performance Liquid Chromatography". Chromatographic conditions: amino column (250 mm × 4.6 mm, 5 μm), mobile phase: anhydrous ethanol, flow rate: 0.8 mL / min, detection wavelength: 326 nm, column temperature: 40℃, injection volume: 10 μL. The sample was dissolved in isopropanol, ultrasonically extracted, filtered through an organic filter membrane, and then diluted to volume before being tested. The mass fraction of γ-Oryzanol in the finished rice bran oil was calculated using the external standard method standard curve.

[0064] (4) Vitamin E content: determined according to GB / T 26635-2011 "Determination of Tocopherol and Tocotrienol Content in Animal and Vegetable Oils by High Performance Liquid Chromatography". Chromatographic conditions: silica gel column (4.6 mm × 250 mm, 5 μm), mobile phase: n-heptane:tetrahydrofuran = 96:4 (V / V), flow rate 1.0 mL / min, excitation wavelength 298 nm, emission wavelength 325 nm, column temperature 30℃, injection volume 10 μL. The sample was dissolved in n-heptane, vortexed, filtered through an organic filter membrane, separated by a silica gel column, and the total content of α-, β-, γ-, and δ-tocopherols in the finished oil was quantitatively determined by external standard method, which is the total vitamin E content.

[0065] Table 1. Test results of the main properties of rice bran oil prepared in each comparative example and the embodiment. As can be seen from Table 1, each example is generally better than the comparative example in terms of leaching rate, residual oil in meal, and content of active ingredients, with Example 3 showing the best performance in all indicators.

[0066] The rice bran oil in Comparative Example 1 underwent only puffing treatment without solid-state fermentation, and its extraction rate and active ingredient content were lower than those in the other examples. This indicates that although simple puffing can inactivate enzymes, stabilize the material, and physically break down cell walls, it does not completely degrade the fiber-encapsulated structure, resulting in limited oil release. Furthermore, high-temperature treatment can cause the loss of heat-sensitive active ingredients.

[0067] The rice bran oil in Example 1 was produced using a puffing pretreatment coupled with a single Bacillus subtilis fermentation process. Compared to the baseline process without fermentation, the extraction rate was increased, the residual oil was reduced, and the content of active ingredients was also improved to some extent. This indicates that the strain mainly promotes oil release by producing enzymes to degrade the fiber encapsulation structure, but its improvement in the antioxidant environment is limited, thus the increase in active ingredients is relatively small.

[0068] The rice bran oil in Example 2, produced using a puffing pretreatment coupled with a single Lactobacillus plantarum fermentation process, showed a similar extraction rate to that of Example 1, but with a significantly higher content of active ingredients. This indicates that the main advantage of Lactobacillus plantarum lies in creating a weakly acidic fermentation environment that inhibits the oxidation of heat-sensitive components, but its ability to degrade fiber and release oil is inferior to that of Bacillus subtilis.

[0069] The rice bran oil in Example 3, produced using a puffing pretreatment coupled with a specific ratio of compound microbial agent fermentation process, achieved the highest levels of extraction rate, residual oil, and active ingredient content, with improvements significantly exceeding half that of Example 1 using a single microbial strain. This indicates that Bacillus subtilis enhances fiber degradation and oil release, while Lactobacillus plantarum improves the antioxidant environment; the synergistic combination of these two technologies achieves simultaneous and optimal oil extraction and quality improvement.

[0070] In Examples 4 and 5, the ratio or amount of Bacillus subtilis / Lactobacillus plantarum in the compound microbial agent differed, and none of the indicators reached the level of Example 3. Specifically, Example 4 reduced the proportion of Lactobacillus plantarum and decreased the total amount of the microbial agent, resulting in insufficient enzyme production and incomplete fiber degradation. Simultaneously, the weakly acidic antioxidant environment was weaker, thus the leaching rate and active ingredient content were lower than in Example 3. Example 5 increased the proportion of Lactobacillus plantarum and increased the total amount of the microbial agent, but the excessively high proportion of Lactobacillus plantarum caused an imbalance in the microbial community structure. The enzyme production and cell wall breaking effect of Bacillus subtilis were inhibited, and excessive microbial metabolism consumed some small molecule nutrients, leading to a decrease in oil extraction efficiency and a less effective enrichment of active ingredients compared to Example 3. It is evident that the ratio and amount of compound microbial agents have a significant impact on the synergistic effect. Too low or too high a ratio will not achieve the optimal oil extraction and quality improvement effect. Only by controlling it within an appropriate range, such as (Bacillus subtilis / Lactobacillus plantarum ratio of 1:1 to 1:1.5, preferably 1:1.1 to 1:1.3), can the synergistic effect of the two strains be fully utilized.

[0071] Comparative Example 2, which uses a direct solid-state fermentation process without puffing, had the lowest extraction rate and active ingredient content among all groups, but the highest residual oil content. This further illustrates that without puffing pretreatment, the dense structure of rice bran remains intact, making it difficult for microbial agents to penetrate and adhere, thus limiting enzymatic hydrolysis. Simultaneously, endogenous enzymes are not inactivated, resulting in poor fermentation stability, and neither oil nor active ingredients can be effectively retained.

[0072] The rice bran oil in Comparative Example 3, produced using a process sequence of solid-state fermentation followed by puffing, showed slightly better performance than Comparative Example 2, but still significantly lower than the example. This is because high-temperature puffing after fermentation severely degrades the enriched heat-sensitive active ingredients, largely negating the quality-improving effect of the initial fermentation. This verifies the necessity of the puffing-fermentation sequence.

[0073] In summary, the results in Table 1 confirm that the present invention achieves a simultaneous increase in the oil extraction rate and active ingredient content of rice bran oil through a segmented coupled process of first puffing and breaking down the cell walls to inactivate enzymes, followed by solid-state fermentation with compound microbial agents to improve the quality. Moreover, the synergistic effect of the compound microbial agents is significantly better than that of single-strain fermentation and traditional physical processes.

[0074] (v) Accelerated storage stability test To verify the storage stability and retention performance of active ingredients in rice bran oil prepared by different processes, accelerated storage tests at 60℃ were conducted on all comparative and example finished oil products. The oils were stored continuously for 15 and 30 days under sealed, light-protected conditions. Samples were taken and the residual contents of γ-oryzanol and vitamin E were measured. The retention rate of active ingredients was calculated using the following formula: Retention rate = (content after storage / initial content) × 100%. The accelerated storage data for each group are shown in Table 2.

[0075] Table 2. Retention rate of active ingredients in rice bran oil of each group during accelerated storage at 60℃ As shown in Table 2, during the accelerated storage process at 60℃, the retention rate of active ingredients in each component of the rice bran oil generally showed a trend that the examples were better than the comparative examples, with Example 3 exhibiting the best storage stability.

[0076] The rice bran oil in Example 1, produced using a puffing pretreatment coupled with a single Bacillus subtilis fermentation process, showed higher retention rates of γ-oryzanol and vitamin E than the baseline process without fermentation, but the improvement was limited. This indicates that the fermentation effect of Bacillus subtilis has a weak effect on improving the antioxidant system of the oil, and the oxidative degradation of active ingredients is still significant under high-temperature storage.

[0077] The rice bran oil in Example 2 was produced using a puffing pretreatment coupled with a single Lactobacillus plantarum fermentation process. Its active ingredient retention rate was higher than that in Example 1, indicating that the weak acid antioxidant system formed by Lactobacillus plantarum metabolism has a good protective effect on heat-sensitive components and can effectively delay oxidative degradation during storage.

[0078] The rice bran oil in Example 3, produced using a fermentation process coupled with a specific ratio of compound microbial agents after puffing pretreatment, exhibited the highest retention rates of γ-oryzanol and vitamin E under the same storage conditions, significantly superior to the single-strain examples and all comparative examples. This demonstrates that the stable, weakly acidic, antioxidant system synergistically constructed by the compound microbial agents not only enhances oil release but also improves the oil's resistance to high-temperature oxidation and thermal degradation, thereby resulting in optimal storage stability and aging resistance of the finished oil.

[0079] The retention rates of active ingredients in rice bran oil in Examples 4 and 5 were between those in Example 3 and the single-strain examples, but neither reached the level of Example 3. In Example 4, the ratio and amount of compound microbial agent were too low, resulting in insufficient antioxidant protection of the product. Although the proportion and total amount of Lactobacillus plantarum were increased in the process of Example 5, the microbial community structure was unbalanced, and the stability of the antioxidant system of the product was not as good as that in Example 3.

[0080] Comparative Example 1, which used a puffing-only process, had a lower retention rate of active ingredients than the other examples, indicating that puffing alone cannot provide effective antioxidant protection, and that active ingredients degrade rapidly under high-temperature storage. Comparative Example 2, which used a direct fermentation process without puffing, had the lowest retention rate of active ingredients due to the lack of inactivation of endogenous enzymes and poor fermentation stability. Comparative Example 3, which used a fermentation-then-puffing process, had its weakly acidic antioxidant system destroyed during subsequent high-temperature puffing, resulting in a similarly low retention rate of active ingredients.

[0081] In summary, the results in Table 2 further verify that rice bran oil prepared by fermentation with a specific ratio of compound microbial agents can improve its storage stability and protect its heat-sensitive active ingredients. Furthermore, the process sequence of puffing followed by fermentation plays a crucial role in maintaining the oil's antioxidant properties.

[0082] In summary, the method for preparing rice bran oil by combining rice bran puffing pretreatment with solid-state fermentation provided by this invention solves the problems of rice bran rancidity during storage and low oil yield and significant loss of functional components due to single physical processing through a segmented coupling process of "puffing first and then solid-state fermentation". At the same time, it avoids the process defects of poor stability of direct fermentation and thermal degradation of puffing after fermentation, so as to simultaneously improve the oil extraction rate, γ-oryzanol content and storage stability, and realize the efficient resource utilization and high-value utilization of rice bran.

[0083] It should be noted that the above embodiments are merely illustrative descriptions of the present invention using specific strain ratios and process parameters as examples. For different rice bran varieties, origins, and initial qualities, those skilled in the art can determine suitable process parameters for specific situations through a limited number of experiments based on the strain ratios, addition amounts, and process parameter ranges provided in this invention, without departing from the essence of the present invention. The specific equipment models listed in the above embodiments (such as twin-screw extruders, constant-temperature closed fermenters, high-performance liquid chromatographs, etc.) can be reasonably selected and adjusted according to actual production conditions, and are not limited to the specific models listed in the embodiments.

[0084] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0085] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing rice bran oil by coupled solid-state fermentation with rice bran puffing, characterized in that, Includes the following steps: (1) Remove impurities from rice bran and control the initial moisture content of rice bran to 8.0% to 10.0% to obtain purified rice bran; (2) The purified rice bran is subjected to wet puffing to obtain puffed rice bran; (3) Inoculate the puffed rice bran with a compound microbial agent and carry out solid-state fermentation to obtain fermented rice bran; the compound microbial agent includes Bacillus subtilis and Lactobacillus plantarum; (4) The fermented rice bran is dried to obtain fermented modified rice bran; (5) The fermented modified rice bran is extracted to obtain rice bran oil.

2. The method according to claim 1, characterized in that, In the compound microbial agent, the mass ratio of Bacillus subtilis powder to Lactobacillus plantarum powder is 1:1 to 1:1.

5.

3. The method according to claim 1, characterized in that, The viable count of the compound microbial agent is not less than 10. 9 The CFU / g, based on the total mass of the compound microbial agent, is added at a rate of 0.2% to 0.5% of the dry weight of the puffed rice bran.

4. The method according to claim 1, characterized in that, In step (2), saturated steam is first introduced to condition the purified rice bran, followed by extrusion and puffing. After puffing, the temperature is lowered to 35-45°C to obtain puffed rice bran. The pressure of the saturated steam is 0.12-0.18 MPa, the conditioning temperature is 65-75°C, the moisture content of the rice bran after conditioning is 11%-13%, and the conditioning time is 3-5 min.

5. The method according to claim 4, characterized in that, The material temperature during extrusion and expansion is 110–125°C, and the die pressure is 3–8 MPa.

6. The method according to claim 1, characterized in that, In step (3), the moisture content of the puffed rice bran is adjusted to 18%–22%, and fermented at 28–32°C for 24–36 h.

7. The method according to claim 1, characterized in that, In step (3), the oxygen volume concentration in the gas phase inside the fermentation vessel is controlled to be 8% to 12%, the carbon dioxide volume concentration is 5% to 8%, and the aeration rate is 0.15 to 0.25 L of sterile air per kilogram of dry weight of puffed rice bran per hour.

8. The method according to claim 1, characterized in that, In step (4), the material temperature does not exceed 55°C during drying, and the material moisture content is dried to 8.0% to 9.0%.

9. The method according to claim 1, characterized in that, In step (5), food-grade n-hexane is used as the leaching solvent, the leaching temperature is 50-55℃, and the leaching time is 90-120 min.

10. A type of rice bran oil, characterized in that, It is prepared by the method according to any one of claims 1 to 9.

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