Defatting black rice embryo preparation process based on density floatation method

Abstract

The application discloses a defatted black rice embryo preparation process based on a density flotation method and belongs to the technical field of rice deep processing. The preparation process comprises the following steps: (1) shelling; (2) rice milling; (3) defatting; (4) density flotation; (5) sample recovery; and (6) drying. The defatted black rice embryo is prepared by simultaneously realizing defatting, bran embryo separation and anthocyanin reservation by treating a black rice bran embryo mixture with a low-polarity lipophilic solvent with suitable density. The process has the advantages of simple steps, good bran embryo separation effect, high rice embryo yield and product comprehensive recovery rate, recyclable solvent, effective reservation of anthocyanin and enrichment of trace nutrients such as gamma-aminobutyric acid, and suitability for wide range of popularization. The obtained product has the advantages of regular appearance, good stability (low fat content and lipase activity, and low rancidity), and high nutritional value (rich in polyphenols, anthocyanin and gamma-aminobutyric acid, etc.). The application has important significance for promoting the deep processing and high-value utilization of black rice.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rice deep processing, and particularly relates to a defatted black rice embryo preparation process based on a density flotation method. BACKGROUND

[0002] Rice (Oryza sativa L.) is an important staple food crop, and its total yield accounts for the third place in the world grain crop yield. More than half of the world's population takes rice as staple food. Black rice is a special rice variety, and its grains (i.e., black rice) are mainly black, rich in anthocyanins, dietary fiber, vitamins, minerals and proteins and other nutrients, has valuable food and medicinal value and wide nutritional and health care effects, and is praised as "blood-enriching rice" and "longevity rice". With the increasing attention of people to healthy diet, black rice and its processed products are increasingly favored by the market and consumers.

[0003] The anatomical structure of rice mainly includes a husk (rice hull), a bran layer (a total name of pericarp, seed coat and aleurone layer), an embryo and an endosperm from outside to inside, wherein the husk is an inedible part and mainly composed of cellulose, hemicellulose and lignin; the bran layer is rich in nutrients such as oil, dietary fiber, protein, polysaccharide, vitamins and minerals; the rice embryo contains rich trace nutrients such as γ-aminobutyric acid, folic acid, tocopherol, glutathione and oryzanol; the bran layer and the rice embryo are important aggregation sites of rice nutrients; and the endosperm of the daily consumed milled rice is mainly composed of starch and a small amount of protein. In the past long period of time, consumers mainly pay attention to the taste and appearance of rice, prefer to select milled rice with endosperm as the absolute main component, and ignore the nutritional value of the bran layer and the rice embryo, resulting in a long-term over-processing phenomenon of rice, and thus a large amount of by-products such as broken rice, rice bran and rice embryo are generated, which not only causes great resource waste, but also causes loss of a large amount of nutrients and environmental pollution problems. According to the estimation, the loss rate of rice in the processing link is as high as 20% in China, and nearly 3.5 million tons of rice are lost every year, 40 million tons of rice hull, 30 million tons of broken rice and 14 million tons of rice bran are generated, and the value-added processing of rice and the high-value utilization of by-products have great potential.

[0004] Rice embryo is an important component of rice, located at the bottom of brown rice grain, containing plumule, hypocotyl, radicle and cotyledon, accounting for about 2%-3% of the mass of paddy. Rice embryo is an important rice processing by-product. During the whitening and peeling process of brown rice, most of the rice embryo falls off and is mixed with the pericarp (pericarp, seed coat, aleurone layer, etc.) to form rice bran. China produces about 4 million tons of rice embryo every year. Rice embryo is one of the most nutrient-dense parts of paddy, rich in nutrients such as carbohydrates, proteins, lipids, vitamins, minerals, and bioactive compounds such as gamma-aminobutyric acid, glutathione, oryzanol, and phytosterols. It is known as "God-given nutrient source" and has high utilization value in food, medicine and cosmetics. However, for a long time, rice embryo has been mixed with rice bran during the milling process and has not been fully developed and utilized separately. The main reason is the difficulty of separating bran and embryo and the quality deterioration caused by high free fatty acid content.

[0005] Currently, the separation and preparation methods of rice embryo or rice germ mainly include wet rinsing separation and dry mechanical separation. Wet rinsing separation is to rinse the bran and broken rice by placing the bran and broken rice treated in a certain way in water. However, this method has limited separation effect and is easy to cause loss of nutrients, and is not suitable for black rice containing a large amount of water-soluble anthocyanins. Dry mechanical separation mainly separates rice embryo by wind selection, rolling and screening processes according to the differences in specific gravity, wind area, suspension speed and oil content of each component in bran and broken rice. However, this method requires special equipment, and the product has high fat content and lipase activity, which is difficult to store. Related research mainly concentrated in the mid-1980s to around 2005, and there were few related reports in the past two decades. The closely related documents include application numbers CN201710082763.9, CN202111546946.4 and CN202223604613.5. However, generally speaking, due to the relatively small amount of rice embryo, the tight combination of bran and embryo, and the high oil content, the separation and preparation of rice embryo generally has the problems of low efficiency, high energy consumption, complex equipment and process, unstable product, etc. The separation and preparation of black rice embryo have not been reported. Therefore, it is of great significance to explore new (black) rice embryo preparation process for the high-quality development of rice deep processing industry. SUMMARY

[0006] In order to overcome the limitations of the traditional preparation method of rice embryos in the prior art and the deficiencies of the preparation process of black rice embryos, the purpose of the present application is to provide a defatted black rice embryo preparation process based on density flotation method, which simultaneously realizes defatting, bran embryo separation and anthocyanin retention by treating (defatting and density flotation) black rice bran embryo mixture with a low-polarity lipophilic solvent with appropriate density, so as to obtain defatted black rice embryos. The method has simple steps, good separation effect, high comprehensive recovery rate, and the solvent can be recycled, which can effectively avoid the instability problem caused by high oil content, and can effectively retain anthocyanins and enrich trace nutrients such as gamma-aminobutyric acid, which has positive significance for realizing the deep processing and high-value utilization of black rice.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A defatted black rice embryo preparation process based on density flotation method, comprising the following steps:

[0009] (1) Dehulling: preferably full, uniform and suitable moisture content black rice paddy, remove the hull of the paddy, to obtain black rice brown rice;

[0010] (2) Rice milling: mill the black rice brown rice obtained in step (1), collect black rice bran containing black rice embryos, i.e. bran embryo mixture;

[0011] (3) Defatting: defat the bran embryo mixture obtained in step (2) with a low-polarity lipophilic solvent with appropriate density, control the solid-liquid ratio, defatting time and stirring speed;

[0012] (4) Density flotation: after defatting, the mixture obtained in step (3) is allowed to float for a period of time, so that the black rice embryos and black rice bran float on the solvent and sink in the solvent respectively due to the difference in density;

[0013] (5) Sample recovery: collect the black rice embryos on the upper layer of the solvent, the black rice bran on the lower layer and the rice bran oil extract in step (4), further rotary evaporate the solvent and obtain rice bran oil;

[0014] (6) Drying: dry the black rice embryos on the upper layer and the black rice bran on the lower layer obtained in step (5) to obtain defatted black rice embryos and defatted black rice bran.

[0015] Preferably, in step (1), the moisture content of the black rice paddy is controlled at 13-16% w / w, and the hull of the paddy is removed by a huller; the huller includes but is not limited to rubber roller huller, sand disc huller and centrifugal huller;

[0016] Further preferably, in step (1), the moisture content of the black rice paddy is controlled at 14-15% w / w, and the huller is an MLGT20 type pressure measure rubber roller huller, and the dehulling rate should be ≥ 90%.

[0017] Preferably, in step (2), the milling is carried out using a rice mill, including but not limited to rubbing-off type, rubbing-cutting type and mixed type rice mill, and the milling degree of black rice (yield of bran-embryo mixture) is controlled at 3% to 12% w / w;

[0018] Further preferably, the rice mill is a PCM-20A rubbing-off type rice mill (kitchen rice mill), and the milling degree of black rice (yield of bran-embryo mixture) is controlled at 4% to 10% w / w, and further at 4% to 7% w / w;

[0019] Preferably, in step (3), the low-polarity lipophilic solvent should have good degreasing ability while retaining the anthocyanins in the bran-embryo mixture, and the density thereof is between the densities of black rice bran and black rice embryo, the solid-liquid ratio is 1 g: 50 mL to 1 g: 5 mL, the degreasing time is 10 to 90 min, and the stirring speed is 100 to 1000 rpm;

[0020] Further preferably, in step (3), the density of the low-polarity lipophilic solvent is 1.20 to 1.50 g / cm 3 (preferably 1.30 to 1.50 g / cm 3 , and further preferably 1.30 to 1.40 g / cm 3 ), the solid-liquid ratio is 1 g: 10 mL, the degreasing time is 45 to 60 min, and the stirring speed is 300 to 600 rpm;

[0021] Further preferably, in step (3), the low-polarity lipophilic solvent is a mixed solvent of dichloromethane, dichloroethane and trichloromethane in any combination of one or more thereof;

[0022] Further preferably, in step (3), the low-polarity lipophilic solvent is a mixed solvent obtained by mixing n-hexane and carbon tetrachloride in a certain proportion to obtain a density of 1.20 to 1.50 g / cm 3 (preferably 1.30 to 1.50 g / cm 3 , and further preferably 1.30 to 1.40 g / cm 3 ).

[0023] Further preferably, in step (3), the low-polarity lipophilic solvent is dichloromethane;

[0024] Preferably, in step (4), the standing and floating time is 10 to 60 min, and attention should be paid to the observation of the residual black rice embryo in the black rice bran, and if there is obvious residue, the system can be stirred again to further separate the black rice embryo from the black rice bran, and further standing and floating;

[0025] Further preferably, in step (4), the standing time of the floatation is 30-45 min.

[0026] Preferably, in step (5), the sample recovery method is: recovering the upper layer black rice embryo with a sieve strainer (40-100 mesh) by filtration, recovering the lower layer black rice bran and the rice bran oil solvent extract by suction filtration (double circle qualitative filter paper, -0.1 MPa), and recovering the solvent and the rice bran oil by rotary evaporation (40-60℃, -0.1 MPa).

[0027] Further preferably, in step (5), the sample recovery method is: recovering the upper layer black rice embryo with a sieve strainer (60-100 mesh) by filtration, recovering the lower layer black rice bran and the rice bran oil solvent extract by suction filtration (double circle qualitative filter paper, -0.1 MPa), and recovering the solvent and the rice bran oil by rotary evaporation (40-50℃, -0.1 MPa).

[0028] Preferably, in step (6), the drying step is: naturally evaporating the black rice embryo in a fume hood until no obvious solvent residue is left, and then drying the black rice embryo in an oven at 40-60℃ for 30-90 min.

[0029] Further preferably, in step (6), the drying step is: naturally evaporating the black rice embryo in a fume hood until no obvious solvent residue is left, and then drying the black rice embryo in an oven at 45-60℃ for 30-60 min.

[0030] Preferably, in step (6), if a small amount of black rice bran floats on the upper layer of the solvent during the density floatation in step (4), the black rice bran is collected together in step (5), dried, and then sieved to obtain defatted black rice embryo, and the small amount of black rice bran is combined with the black rice bran collected in step (5).

[0031] Further preferably, the sieving is sieving through a 40-60 mesh sieve.

[0032] A defatted black rice embryo, a defatted black rice bran, and a rice bran oil prepared by the above preparation process.

[0033] The defatted black rice embryo prepared by the above technical solution has a yield of 3.63%-11.60% (relative to the bran-embryo mixture, the same below), the defatted black rice bran has a yield of 67.88%-80.45%, the rice bran oil has a yield of 12.17%-15.13%, the comprehensive recovery rate is 92.87%-99.51%, the solvent recovery rate is 68.33%-87.00%, the yield of the defatted black rice embryo, the comprehensive recovery rate, and the solvent recovery rate are high.

[0034] The defatted black rice embryo prepared by the above technical solution has a regular and uniform appearance, and macroscopically presents uniform black and white flat granular particles, and microscopically presents a visual impression similar to the section of a raw oyster. Figure 3);In the embodiment (Table 3), the fat content of the defatted black rice embryo is 1.69% to 2.02%, the lipase activity is 5.50 to 6.19 mg / g, which is significantly lower than that of black rice and black rice bran, and the acid value does not increase significantly after 60 days of storage at room temperature, and the stability is good; the anthocyanin content of the defatted black rice embryo is 4.12 to 6.58 mg / g, the gamma-aminobutyric acid content is 21.02 to 28.37 mg / 100g, and the total phenol content is 9.60 to 11.89 mg GAE / g DW, which is significantly higher than that of black rice, indicating that the above nutrient components are enriched in the defatted black rice embryo, and the defatted black rice embryo has high nutritional value;

[0035] The technical principle of the present application is as follows: Figure 2 According to the difference in the relative density of bran embryos, the bran embryo mixture is treated with a low-polarity lipophilic solvent with a density between the two, and under the action of gravity, the black rice bran with high density sinks, and the black rice embryo with low density floats, achieving bran embryo separation, while the low-polarity lipophilic solvent effectively extracts rice bran oil and retains anthocyanin, improving the oxidation stability and nutritional value of the product.

[0036] The present application has the following advantages and effects compared with the prior art:

[0037] (1) The present application uses solvent density flotation method to effectively separate black rice embryo and rice bran under the action of gravity, while extracting rice bran oil (the main factor causing unstable mass of rice bran and rice embryo) and retaining anthocyanin (the main functional factor of black rice and its processed products). The simultaneous defatting, bran embryo separation and anthocyanin retention based on solvent density flotation method is a significant beneficial effect that the prior art methods do not have.

[0038] (2) The process steps of the present application are simple, the bran embryo separation effect is good, the rice embryo yield and the comprehensive recovery rate of the product are high, the solvent can be recycled, and defatted black rice embryo, defatted black rice bran and rice bran oil are obtained at the same time, which is suitable for wide promotion. In specific embodiments, the defatted black rice embryo yield is 3.63% to 11.60% (relative to the bran embryo mixture, the same below), the defatted black rice bran yield is 67.88% to 80.45%, the rice bran oil yield is 12.17% to 15.13%, and the comprehensive recovery rate is 92.87% to 99.51%, and the solvent recovery rate is 68.33% to 87.00%;

[0039] (3) The present application prepares defatted black rice embryo with regular morphology, good stability (low fat content and lipase activity, not prone to rancidity), and high nutritional value (rich in functional factors such as polyphenols, anthocyanins and gamma-aminobutyric acid), and the separation and preparation process of black rice embryo is rarely reported.

[0040] (4) Compared with traditional dry mechanical separation, the required instruments and tools of the present application are simple, without the need for custom-made special mechanical equipment, and synchronous defatting can be achieved; compared with (water) wet rinsing separation, the present application can be particularly applied to black rice germ separation, without causing loss of characteristic nutritional components anthocyanins;

[0041] (5) The present application provides a simple bran, germ and oil separation method, which lays a good process and raw material foundation for further enrichment and preparation of characteristic functional active factors of each part (such as anthocyanins / dietary fiber in black rice bran, vitamins / γ-aminobutyric acid in germ, and oryzanol / plant sterols in rice bran oil), which is of great significance to promote the deep processing and high-value utilization of black rice. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a process flow diagram of the present application;

[0043] Figure 2 is a schematic diagram of the bran and germ separation principle based on density flotation method;

[0044] Figure 3 is the macroscopic and microscopic morphology diagram of defatted black rice germ obtained from Examples 1-6 (corresponding to (A)-(F)). DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and beneficial effects of the present application clearer and more apparent, the exemplary embodiments of the present disclosure will be described in more detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, and the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein.

[0046] In the examples, the fat content was determined according to GB 5009.6-2016; the lipase activity was determined according to GB / T5523-2008; the anthocyanin content was determined by pH differential method according to the method of Pang et al. (Reference 1), and the anthocyanin content was expressed as milligram equivalent of cyanidin-3-O-glucoside (Cy 3-Glu) per gram of sample; the total phenol content was determined by Folin-Ciocalteu method according to the method of Zhang (Reference 2) and Hu Ting (Reference 3) using gallic acid as a standard, and the total phenol content was expressed as milligram equivalent of gallic acid per gram of sample dry weight, i.e. mg GAE / g DW; the γ-aminobutyric acid content was determined by colorimetric detection kit (Wuhan Elabscience Biotechnology Co., Ltd., Item No.: E-BC-K852-M) according to the operating instructions.

[0047] Reference 1: Pang Y., Ahmed S., Xu Y., Beta T., Zhu Z., Shao Y., Bao J. Bound phenolic compounds and antioxidant properties of whole grain and bran of white, red and black rice [J]. Food Chemistry, 2018, 240: 212-221.

[0048] Reference 2: Zhang M.W., Zhang R.F., Zhang F.X., Liu R.H. Phenolic Profiles and Antioxidant Activity of Black Rice Bran of Different Commercially Available Varieties [J]. Journal of Agricultural and Food Chemistry, 2010, 58(13): 7580-7587.

[0049] Reference 3: Hu T, Wang X, Geng KZ, et al. Effects of ultrafine grinding on the composition and activity of polyphenols in black rice bran [J / OL]. Modern Food Science and Technology, 1-9. https: / / doi.org / 10.13982 / j.mfst.1673-9078.2024.12.0068.

[0050] The process flow chart of the present application is shown in Figure 1 .

[0051] Example 1

[0052] A defatted black rice embryo preparation process based on density flotation method, comprising the following steps:

[0053] (1) Dehulling: preferably full, uniform, and moisture content of 15% w / w black rice paddy, using MLGT20 type pressure weight rubber roller huller to remove the hull of the paddy, controlling the dehulling rate at 90%, to obtain black rice brown rice;

[0054] (2) Rice milling: using PCM-20A rubbing-off type rice mill to select 7 fraction grinding degree to mill the black rice brown rice obtained in step (1), 320g each time, controlling the grinding degree (furfuraceous embryo mixture yield) at about 7% w / w, collecting black rice bran containing black rice embryo (furfuraceous embryo mixture);

[0055] (3) Defatting: 10.00 g of the bran-embryo mixture obtained in step (2) was weighed into a 250 mL three-necked flask, 100 mL of dichloroethane was added, and the mixture was stirred at room temperature at 300 rpm for 1.0 h;

[0056] (4) Density floatation: After defatting, the mixture obtained in step (3) was allowed to stand for 30 min, so that the black rice embryos and black rice bran floated on the solvent and sank in the solvent, respectively;

[0057] (5) Sample recovery: The black rice embryos on the solvent were recovered by filtering with a 60-mesh sieve strainer, and the rice bran oil solvent extract (filtrate) and the lower layer of black rice bran (filter cake) were recovered by vacuum filtration (double-circle qualitative filter paper, -0.1 MPa). Dichloroethane and rice bran oil were further recovered by rotary evaporation (50°C, -0.1 MPa);

[0058] (6) Drying: The black rice embryos and black rice bran obtained in step (5) were naturally volatilized to dryness in a fume hood, and then dried in an oven at 50°C for 60 min to obtain defatted black rice embryos and defatted black rice bran.

[0059] The defatted black rice embryos, defatted black rice bran, and rice bran oil obtained in Example 1 had a yield of 5.63%, 80.45%, and 13.43%, respectively, and the comprehensive recovery rate was 99.51%, and the solvent (dichloroethane) recovery rate was 87.00%.

[0060] The defatted black rice embryos obtained in Example 1 had a fat content of 1.80%, a lipase activity of 5.79 mg / g, an anthocyanin content of 4.34 mg / g, a γ-aminobutyric acid content of 21.02 mg / 100 g, a total phenol content of 9.76 mg GAE / g DW, and a regular and uniform morphology (A). Figure 3

[0061] Example 2

[0062] A defatted black rice embryo preparation process based on the density floatation method, comprising the following steps:

[0063] (1) Dehulling: Preferably, the black rice grains with a moisture content of 14% w / w were dehulled by using an MLGT20 type presser roller rubbing machine to control the dehulling rate at 90%, to obtain black rice brown rice;

[0064] (2) Rice milling: The black rice brown rice obtained in step (1) was milled by using a PCM-20A rubbing type rice mill at a milling degree of 7%, 160 g at a time, and the milling degree (bran-embryo mixture yield) was controlled at about 7% w / w, and the black rice bran containing black rice embryos (bran-embryo mixture) was collected;

[0065] ​(3) Defatting: 10.00 g of the bran-embryo mixture obtained in step (2) was weighed, 100 mL of dichloromethane was added, and the mixture was uniformly mixed and then defatted at room temperature for 1.0 h under magnetic stirring at 600 rpm;

[0066] (4) Density flotation: After defatting, the mixed system obtained in step (3) was allowed to stand for 30 min, so that the black rice embryos and black rice bran floated on and sank under the solvent, respectively;

[0067] (5) Sample recovery: The black rice embryos on the solvent layer were recovered by filtration using a 60-mesh sieve strainer, and the rice bran oil solvent extract (filtrate) and the lower layer of black rice bran (filter cake) were recovered by vacuum filtration (double-circle qualitative filter paper, -0.1 MPa). Dichloromethane and rice bran oil were further recovered by rotary evaporation (45°C, -0.1 MPa);

[0068] (6) Drying: The black rice embryos and black rice bran obtained in step (5) were respectively dried in a fume hood until no obvious solvent residue was observed, and then dried in an oven at 50°C for 60 min to obtain defatted black rice embryos and defatted black rice bran.

[0069] According to Example 2, the defatted black rice embryo, defatted black rice bran, and rice bran oil yield were 10.42%, 75.23%, and 12.17%, respectively, and the comprehensive recovery rate was 97.81%, and the solvent (dichloromethane) recovery rate was 68.33%.

[0070] The fat content of the defatted black rice embryo obtained by Example 2 was 1.79%, the lipase activity was 5.50 mg / g, the anthocyanin content was 4.26 mg / g, the γ-aminobutyric acid content was 23.86 mg / 100 g, the total phenol content was 10.66 mg GAE / g DW, and the morphology was regular and uniform Figure 3 (B).

[0071] Example 3

[0072] A defatted black rice embryo preparation process based on the density flotation method, comprising the following steps:

[0073] (1) Dehulling: Preferably, the black rice paddy with a moisture content of 14% w / w was dehulled using an MLGT20 type presser roller huller to control the dehulling rate at 90%, and black rice brown rice was obtained;

[0074] (2) Rice milling: The black rice brown rice obtained in step (1) was milled using a PCM-20A rubbing type rice mill at a milling degree of 5 minutes, 160 g was milled each time, and the milling degree (bran-embryo mixture yield) was controlled at about 4% w / w, and the black rice bran containing black rice embryos (bran-embryo mixture) was collected;

[0075] (3) Defatting: 10.00 g of the bran mixture obtained in step (2) was weighed, 100 mL of chloroform was added, and the mixture was uniformly mixed and then defatted at room temperature with magnetic stirring at 500 rpm for 1.0 h;

[0076] (4) Density flotation: After defatting, the mixed system obtained in step (3) was allowed to stand for 45 min, so that the black rice embryos and black rice bran were separated due to the difference in density under the driving of gravity;

[0077] (5) Sample recovery: The upper layer of black rice embryos (containing a small amount of black rice bran) was recovered by filtering with a 60-mesh sieve strainer, and the rice bran oil solvent extract (filtrate) and the lower layer of black rice bran (filter cake) were recovered by vacuum filtration (double-circle qualitative filter paper, -0.1 MPa). Further rotary evaporation (40°C, -0.1 MPa) was used to recover chloroform and rice bran oil;

[0078] (6) Drying and sieving: The black rice embryos (containing a small amount of black rice bran) and black rice bran obtained in step (5) were respectively dried in a fume hood until no obvious solvent residue was observed, and then dried in an oven at 45°C for 60 min. A small amount of black rice bran was removed by sieving through a 40-mesh sieve (undersize), and defatted black rice embryos (retained fraction) and defatted black rice bran were prepared.

[0079] It should be noted that, due to the relatively large density of chloroform (1.48 g / cm 3 ), a small amount of black rice bran floated on the upper layer of the solvent during the density flotation process in step (4). In step (5), it was filtered out together, dried, and then sieved through a 40-mesh sieve to obtain defatted black rice embryos, and a small amount of black rice bran was combined with the black rice bran recovered in step (5).

[0080] Through Example 3, the defatted black rice embryos, defatted black rice bran, and rice bran oil yield were 11.33%, 70.04%, and 12.90%, respectively, and the comprehensive recovery rate was 94.26%, and the solvent (chloroform) recovery rate was 79.30%.

[0081] The fat content of the defatted black rice embryos obtained by Example 3 was 2.02%, the lipase activity was 5.84 mg / g, the anthocyanin content was 6.58 mg / g, the γ-aminobutyric acid content was 27.21 mg / 100 g, the total phenol content was 11.89 mg GAE / g DW, and the morphology was regular and uniform Figure 3 (C).

[0082] Example 4

[0083] A defatted black rice embryo preparation process based on the density flotation method, comprising the following steps:

[0084] (1) Hulling: Preferably, black rice grains with fullness, uniformity, and moisture content of 15% w / w were used. The hulling was performed using an MLGT20 type presser roller huller to remove the hulls of the rice grains, and the hulling rate was controlled at 90%. The black rice husked rice was obtained.

[0085] (2) Milling: The black rice husked rice obtained in step (1) was milled using a PCM-20A rubbing-off type rice mill with a milling degree of 7 divisions. Each time, 160 g of the black rice husked rice was milled, and the milling degree (the yield of the bran-embryo mixture) was controlled at about 7% w / w. The black rice bran (bran-embryo mixture) containing black rice embryos was collected.

[0086] (3) Defatting: 10.00 g of the bran-embryo mixture obtained in step (2) was weighed, and 100 mL of a mixed solvent of dichloroethane and dichloromethane at a volume ratio of 1:1 was added. After mixing, the defatting was performed at room temperature for 1.0 h with magnetic stirring at 450 rpm.

[0087] (4) Density flotation: After the defatting was completed, the mixed system obtained in step (3) was allowed to stand for 45 min, so that the black rice embryos and the black rice bran were floated on the solvent and sank in the solvent, respectively.

[0088] (5) Sample recovery: The black rice embryos on the solvent layer were recovered by filtering with a 100-mesh sieve strainer, and the rice bran oil solvent extract (filtrate) and the lower layer black rice bran (filtrate cake) were recovered by vacuum filtration (double-circle qualitative filter paper, -0.1 MPa). Further, the solvent and the rice bran oil were recovered by rotary evaporation (50°C, -0.1 MPa).

[0089] (6) Drying: The black rice embryos and the black rice bran obtained in step (5) were naturally volatilized to dryness in a fume hood, and then dried in an oven at 50°C for 60 min to obtain defatted black rice embryos and defatted black rice bran.

[0090] Through Example 4, the defatted black rice embryo, the defatted black rice bran, and the rice bran oil yield were 6.51%, 78.87%, and 12.70%, respectively, and the comprehensive recovery rate was 98.08%, and the solvent (mixed solvent of dichloroethane and dichloromethane) recovery rate was 74.33%.

[0091] The fat content of the defatted black rice embryo obtained through Example 4 was 1.94%, the lipase activity was 6.19 mg / g, the anthocyanin content was 4.03 mg / g, the γ-aminobutyric acid content was 21.02 mg / 100 g, the total phenol content was 9.85 mg GAE / g DW, and the morphology was regular and uniform. Figure 3 (D).

[0092] Example 5

[0093] A defatted black rice embryo preparation process based on a density flotation method, comprising the following steps:

[0094] (1) Hulling: Preferably, the black rice grains with fullness, uniformity and moisture content of 14% w / w were dehulled by using MLGT20 type presser roller huller to remove the hulls of the rice grains, and the dehulling rate was controlled at 90%, to obtain the black rice husked rice;

[0095] (2) Milling: The black rice husked rice obtained in step (1) was milled by using PCM-20A rubbing-off type rice mill with a milling degree of 7%, 160 g each time, and the milling degree (the yield of bran-embryo mixture) was controlled at about 7% w / w, to collect the black rice bran (bran-embryo mixture) containing black rice embryos;

[0096] (3) Defatting: 10.00 g of the bran-embryo mixture obtained in step (2) was weighed, 100 mL of a mixed solvent of dichloroethane and chloroform with a volume ratio of 1:1 was added, and the mixture was uniformly mixed and then stirred at room temperature at 600 rpm for 45 min;

[0097] (4) Density flotation: After defatting, the mixed system obtained in step (3) was allowed to stand for 45 min, so that the black rice embryos and the black rice bran were respectively floated on the solvent and sunk in the solvent;

[0098] (5) Sample recovery: The black rice embryos on the solvent were recovered by using a 60-mesh sieve strainer, and the bran oil solvent extract (filtrate) and the lower layer black rice bran (filtrate) were recovered by vacuum filtration (double-circle qualitative filter paper, -0.1 MPa), and further rotary evaporation (45°C, -0.1 MPa) was performed to recover the solvent and the bran oil;

[0099] (6) Drying: The black rice embryos and the black rice bran obtained in step (5) were respectively naturally volatilized in a fume hood until no obvious solvent residue was observed, and then were placed in an oven at 60°C for 30 min, to obtain defatted black rice embryos and defatted black rice bran.

[0100] Through Example 5, the defatted black rice embryo, the defatted black rice bran and the bran oil yield were 10.66%, 67.88% and 14.33% respectively, the comprehensive recovery rate was 92.87%, and the solvent (dichloroethane and chloroform) recovery rate was 81.17%.

[0101] The fat content of the defatted black rice embryo obtained through Example 5 was 1.82%, the lipase activity was 5.93 mg / g, the anthocyanin content was 4.12 mg / g, the γ-aminobutyric acid content was 21.93 mg / 100 g, the total phenol content was 9.60 mg GAE / g DW, and the morphology was regular and uniform (E). Figure 3 Example 6

[0102] A defatted black rice embryo preparation process based on the density flotation method, comprising the following steps:

[0103]

[0104] ​(1) Dehulling: Select plump, uniform black rice paddies with a moisture content of 15% w / w, and use an MLGT20 type roller huller to remove the hulls of the rice paddies, controlling the dehulling rate to 90%, to obtain black rice brown rice.

[0105] (2) Rice milling: Use a PCM-20A wiping rice milling machine to mill the black rice brown rice obtained in step (1) at a milling degree of 7. Mill 320g each time, control the milling degree (yield of bran-embryo mixture) at about 7% w / w, and collect the black rice bran (bran-embryo mixture) containing black rice embryos.

[0106] (3) Degreasing: Weigh 10.00g of the bran mixture obtained in step (2), add 100mL of a 1:1 mixture of dichloromethane and trichloromethane, mix evenly, and then degrease at 500rpm magnetic stirring at room temperature for 60min.

[0107] (4) Density flotation: After defatting, let the mixture obtained in step (3) stand for 30 minutes so that the black rice germ and black rice bran float on the solvent and sink below the solvent, respectively.

[0108] (5) Sample recovery: The upper black rice germ was filtered and the solvent was recovered by using a 60-mesh sieve strainer. The rice bran oil solvent extract (filtrate) and the lower black rice bran (filter cake) were recovered by vacuum filtration (double-ring qualitative filter paper, -0.1MPa). Further rotary evaporation (50℃, -0.1MPa) was carried out to recover the solvent and rice bran oil.

[0109] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally dried in a fume hood until there is no obvious solvent residue, and then placed in a 50℃ oven for 60 minutes to prepare defatted black rice germ and defatted black rice bran.

[0110] In Example 6, the yields of defatted black rice germ, defatted black rice bran, and rice bran oil were 11.33%, 71.09%, and 15.13%, respectively, with a comprehensive recovery rate of 97.54% and a solvent (dichloromethane and trichloromethane) recovery rate of 76.00%.

[0111] The defatted black rice germ obtained in Example 6 had a fat content of 1.69%, lipase activity of 5.97 mg / g, anthocyanin content of 4.20 mg / g, γ-aminobutyric acid content of 28.37 mg / 100g, and total phenol content of 9.83 mg GAE / gDW. It also exhibited a regular and uniform morphology. Figure 3 (F)).

[0112] Example 7

[0113] Solvent selection and density determination in density flotation:

[0114] (1) Solvent selection:

[0115] Accurately weigh 1.0 g of black rice bran containing black rice embryos (7th grinding degree) into a 15 mL sample bottle (14 parts), and add 10 mL of petroleum ether, n-hexane, cyclohexane, carbon tetrachloride, diethyl ether, dichloromethane, dichloroethane, ethanol, ethyl acetate, isopropyl alcohol, chloroform, acetone, methanol, and water, respectively. Stir at 600 rpm at room temperature for 1.0 h, and then stand for about 1.0 h to observe the phenomenon of the extraction system. Then transfer all the extract into a centrifuge tube, and centrifuge at 8000 rpm for 3.0 min to observe the phenomenon of the extract.

[0116] The results show that the black rice embryos float on the upper layer of the dichloromethane, dichloroethane, and chloroform extraction systems, and the bran embryo mixture floats on the upper layer of the carbon tetrachloride extraction system. The bran embryo mixture sinks in the solvent in the remaining solvent extraction systems. After centrifugation, it is found that the extracts of the petroleum ether, n-hexane, cyclohexane, carbon tetrachloride, diethyl ether, dichloromethane, dichloroethane, ethyl acetate, chloroform, and acetone extraction systems have no obvious purple or red color, and the extracts of ethanol, isopropyl alcohol, methanol, and water show the typical red or purple-black color of anthocyanins. The above results suggest that dichloromethane, dichloroethane, and chloroform can be used as bran embryo separation solvents, and can retain the characteristic nutritional ingredient anthocyanin.

[0117] (2) Determination of the density of the density floatation solvent:

[0118] To determine the suitable solvent density for bran embryo separation, n-hexane and carbon tetrachloride were mixed in a certain proportion to prepare gradient density solvents with densities of 1.10-1.50 g / cm 3 (25°C), and then the operation was carried out according to the conditions and parameters described in Example 2, except that dichloromethane was replaced by the above gradient density solvents, and the sieving step described in Example 3 step (6) was added if necessary. The bran embryo floatation separation effect of different density solvents was investigated with the defatted black rice embryo yield as the evaluation index, and the results are shown in Table 1.

[0119] Table 1 Bran embryo floatation separation effect of different density solvents

[0120]

[0121] The results (Table 1) show that solvents with densities in the range of 1.20-1.50 g / cm 3 can achieve a certain bran embryo separation effect, and the defatted black rice embryo yield is between 3.63% and 11.60%. The bran embryo separation effect is best when the solvent density is 1.30, 1.35, and 1.40 g / cm 3 . When the solvent density is lower than 1.30 g / cm 3 , the black rice embryos have a tendency to suspend or sink, and when the solvent density is lower than 1.20 g / cm 3, the bran-embryo mixture all sinks in the solvent lower layer, and the black rice embryo cannot be obtained; correspondingly, when the solvent density is higher than 1.40 g / cm 3 , the black rice bran has a suspension or floating tendency, and a certain amount of black rice bran is mixed in the subsequently collected black rice embryo, and a sieving step as described in step (6) of Example 3 needs to be added. Further verification is carried out according to the conditions and parameters described in Example 1 by using dichloromethane with a density of 1.325 g / cm 3 , and the yield of defatted black rice embryo is 10.68%. The above results show that the bran-embryo separation density flotation solvent density should be between 1.20-1.50 g / cm 3 , preferably 1.30-1.40 g / cm 3 , and further preferably dichloromethane with a density of 1.325 g / cm 3 .

[0122] Comparative Example 1

[0123] The difference between Example 2 and Comparative Example 1 is that n-hexane is used instead of dichloromethane in step (3).

[0124] Comparative Example 2

[0125] The difference between Example 2 and Comparative Example 2 is that methanol is used instead of dichloromethane in step (3).

[0126] Comparative Example 3

[0127] The difference between Example 2 and Comparative Example 3 is that the grinding degree (bran-embryo mixture yield) is controlled at 14.80% in step (2).

[0128] According to the processes described in Examples 1-6 and Comparative Examples 1-3, the yield of defatted black rice embryo, the yield of defatted black rice bran, the yield of rice bran oil, the comprehensive recovery rate and the solvent recovery rate are shown in Table 2.

[0129] Table 2 Bran-embryo separation effect data comparison of examples and comparative examples

[0130]

[0131] As can be seen from Table 2, according to the design spirit of the present application, Examples 1-6 can all achieve bran-embryo separation to obtain defatted black rice embryo, especially when the solvent density is between 1.30-1.50 g / cm 3The intact black rice embryo in the rice bran embryo mixture can be almost completely recovered, and the yield can reach more than 10% (Examples 2, 3, 5, and 6). In Comparative Examples 1 and 2, n-hexane and methanol are respectively used to replace the solvent described in Example 2, and the results show that the black rice embryo is all settled under the solvent, and the separation of the rice bran embryo cannot be achieved, and the extract of the methanol defatted floating system is purple black, and the yield of the rice bran oil (solvent extract residue) is significantly higher, indicating that a large amount of anthocyanins and other substances are extracted, which will lead to the loss of nutritional ingredients in the product (defatted rice bran). In Comparative Example 3, a rice bran embryo mixture with a higher grinding degree is used, and the yield of the defatted black rice embryo is significantly lower than that of Example 2, which may be because the structure of the intact rice embryo is damaged when the grinding degree is higher, resulting in a decrease in the amount of the rice embryo floating in the density flotation process. The comprehensive recovery rate of the products of Examples 1-6 can all reach more than 90% (92.87%-99.51%), and the solvent recovery rate is also in a considerable range (68.33%-87.00%).

[0132] According to the processes described in Examples 1-6 and Comparative Example 3, the data of the stability and nutritional index of the defatted black rice embryo, such as the fat content, lipase activity, anthocyanin, γ-aminobutyric acid, and total phenol content, are shown in Table 3.

[0133] Table 3 Stability and nutritional index data of the defatted black rice embryo prepared in Examples and the control samples thereof

[0134]

[0135] As can be seen from Table 3, according to the design spirit of the present application, the fat content and lipase activity of the defatted black rice embryo obtained in Examples 1-6 are significantly lower than those of the black rice and black rice bran. Lipase-mediated lipid hydrolysis is an important factor causing oxidation and rancidity and quality deterioration of grain processing products, and therefore the defatted black rice embryo obtained by using the process of the present application has better oxidation stability than the black rice and black rice bran, and is beneficial to long-term preservation. In terms of nutritional index, the contents of anthocyanin, γ-aminobutyric acid, and total phenol of the defatted black rice embryo are all greatly improved compared with those of the black rice (since anthocyanin and phenols mainly exist in the skin layer, the contents of these two components in the black rice bran are still higher than those in the defatted black rice embryo). The content of γ-aminobutyric acid in the defatted black rice embryo is also greatly improved compared with that in the black rice bran, which is because γ-aminobutyric acid mainly exists in the rice embryo, and is a water-soluble nutritional element, which is less dissolved in the solvent defatting and density flotation process, and is better retained in the defatted black rice embryo. The above results show that the defatted black rice embryo obtained by the process of the present application has good stability and high nutritional value.

[0136] In summary, the application provides a simple, efficient and multi-benefit defatted black rice embryo preparation process based on the density flotation principle, realizes bran embryo separation, effectively avoids product stability problems caused by fat and lipase, retains active factors anthocyanins, and obtains defatted black rice embryos with high stability (low fat content and lipase activity) and high nutritional value (rich in polyphenols, anthocyanins and gamma-aminobutyric acid), thereby expanding technical experience for deep processing and high-value utilization of rice, especially black rice.

[0137] The above embodiment is a preferred embodiment of the application, but the embodiments of the application are not limited to the above embodiment, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the application should be equivalent replacement methods, and are all included in the protection scope of the application.

Claims

1. A process for preparing defatted black rice germ based on density flotation, characterized in that, Includes the following steps: (1) Dehulling: Select plump, uniform black rice grains with appropriate moisture content, remove the hulls of the rice grains to obtain black rice brown rice; (2) Rice milling: The black rice brown rice obtained in step (1) is milled, and the black rice bran containing black rice germ is collected, i.e., bran-germ mixture; (3) Degreasing: The bran-embryo mixture obtained in step (2) is degreased with a low-polarity lipophilic solvent of suitable density, and the material-liquid ratio, degreasing time and stirring speed are controlled; the density of the low-polarity lipophilic solvent is between that of black rice bran and black rice embryo, the material-liquid ratio is 1 g: 50 mL to 1 g: 5 mL, the degreasing time is 10 to 90 min and the stirring speed is 100 to 1000 rpm; (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for a period of time for flotation, so that the black rice germ and black rice bran float on the solvent and sink below the solvent respectively due to their different densities; (5) Sample recovery: Collect the upper black rice germ, lower black rice bran and rice bran oil extract of the solvent in step (4) respectively, and further recover the solvent by rotary evaporation to obtain rice bran oil; (6) Drying: The upper black rice germ and the lower black rice bran obtained in step (5) are dried thoroughly to obtain defatted black rice germ and defatted black rice bran.

2. The process for preparing defatted black rice germ based on density flotation according to claim 1, characterized in that: In step (3), the density of the low-polarity lipophilic solvent should be between 1.20 and 1.50 g / cm³. 3 The material-to-liquid ratio is 1 g: 10 mL, the degreasing time is 45–60 min, and the stirring speed is 300–600 rpm.

3. The process for preparing defatted black rice germ based on density flotation according to claim 1, characterized in that: In step (3), the low-polarity lipophilic solvent is a mixture of one or more of dichloromethane, dichloroethane, and chloroform, or has a density of 1.20–1.50 g / cm³. 3 A mixed solvent of n-hexane and carbon tetrachloride.

4. The process for preparing defatted black rice germ based on density flotation according to any one of claims 1 to 3, characterized in that: In step (1), the moisture content of the black rice is controlled at 13% to 16% w / w; In step (2), the yield of the bran-embryo mixture is controlled to be between 3% and 12% w / w.

5. The defatted black rice germ preparation process based on density flotation according to claim 4, characterized in that: In step (1), the moisture content of the black rice paddies is controlled at 14%–15% w / w, and the dehulling rate is ≥90%. In step (2), the yield of the bran-embryo mixture is controlled at 4% to 10% w / w.

6. The process for preparing defatted black rice germ based on density flotation according to any one of claims 1 to 3, characterized in that: In step (4), the settling and flotation time is 10 to 60 minutes. Attention should be paid to observing the residue of black rice germ in black rice bran. If there is obvious residue, the system should be stirred again to further separate the two, and then settling and flotation should be carried out again. In step (5), the conditions for rotary evaporation are 40–60 °C and -0.1 MPa; In step (6), the drying step is as follows: the black rice germ is naturally evaporated until there is no obvious solvent residue, and then placed in 40-60 ℃ to dry for 30-90 min.

7. The defatted black rice germ preparation process based on density flotation according to claim 6, characterized in that: In step (4), the settling and flotation time is 30 to 45 minutes; In step (5), the conditions for rotary evaporation are 40–50 °C and -0.1 MPa; In step (6), the drying step is as follows: the black rice germ is naturally evaporated until there is no obvious solvent residue, and then placed in 45-60 ℃ to dry for 30-60 min.

8. The process for preparing defatted black rice germ based on density flotation according to any one of claims 1 to 3, characterized in that: In step (6), if a small amount of black rice bran floats on the solvent during the density flotation process in step (4), it is collected together in step (5), dried, and then sieved to obtain defatted black rice germ. The small amount of black rice bran obtained is combined with the black rice bran collected in step (5).

9. A defatted black rice germ, defatted black rice bran, and rice bran oil prepared by the preparation process described in any one of claims 1 to 8.

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