Degreased black rice embryo preparation process based on density flotation method

Abstract

The invention discloses a degreased 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) degreasing; (4) density flotation; (5) sample recovery; and (6) drying. According to the method, a low-polarity lipophilic solvent with proper density is used for treating a black rice bran embryo mixture, degreasing, bran embryo separation and anthocyanin retention are synchronously realized, and the degreased black rice embryo is prepared. The process is simple in step, good in bran and embryo separation effect, high in rice embryo yield and product comprehensive recovery rate, recyclable in solvent, capable of effectively retaining anthocyanin and enriching micronutrient elements such as gamma-aminobutyric acid and suitable for large-scale popularization; the obtained product is regular in morphology, good in stability (low in fat content and lipase activity and not prone to rancidification) and high in nutritional value (rich in polyphenol, anthocyanin, gamma-aminobutyric acid and the like). The method disclosed by the invention is of great significance in promoting deep processing and high-value utilization of the black rice.

Description

Technical Field

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

[0002] Rice (Oryza sativa L.) is an important staple food crop, with the total output ranking third in the world's food crop output. More than half of the world's population relies on rice as their staple food. Black rice is a special rice variety, with black grains (i.e. black rice) as the main color. It is rich in nutrients such as anthocyanins, dietary fiber, vitamins, minerals, and protein. It has valuable therapeutic and medicinal value and a wide range of nutritional and health benefits. It is known as "blood-replenishing rice" and "longevity rice". As people pay more attention to healthy diet, black rice and its processed products are increasingly favored by the market and consumers.

[0003] The anatomical structure of rice from the outside to the inside mainly includes the husk (rice husk), bran layer (a general term for pericarp, seed coat, and endosperm), embryo and endosperm. The husk is an inedible part, mainly composed of cellulose, hemicellulose and lignin; the bran layer is rich in nutrients such as oil, dietary fiber, protein, polysaccharides, vitamins, minerals, etc., and the rice germ is rich in micronutrients such as γ-aminobutyric acid, folic acid, tocopherol, glutathione and oryzanol. The bran layer and rice germ are important accumulation sites of rice nutrients; the polished rice consumed daily is the rice endosperm, the main components of which are starch and a small amount of protein. For a long time in the past, consumers have mainly focused on the taste and appearance of rice, and prefer to choose polished rice with endosperm as the absolute main component, ignoring the nutritional value of the bran layer and rice germ, resulting in long-term over-processing of rice, resulting in a large number of by-products such as broken rice, rice bran and rice germ, which not only causes a huge waste of resources, but also loses a large amount of nutrients, while also causing environmental pollution problems. It is estimated that the loss rate in my country's rice processing link is as high as 20%, with nearly 3.5 million tons of rice lost each year, resulting in 40 million tons of rice husks, 30 million tons of broken rice and 14 million tons of rice bran. There is huge potential for value-added processing of rice and high-value utilization of its by-products.

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

[0005] At present, the separation and preparation methods of rice germ or rice germ mainly include wet rinsing separation and dry mechanical separation. The wet rinsing separation is to rinse the bran after a certain treatment in water to remove the bran flakes and broken rice, but this method has limited separation effect, easily causes the loss of nutrients, and is not suitable for black rice containing a large amount of water-soluble anthocyanins; dry mechanical separation is mainly based on the difference in the specific gravity, wind-receiving area, suspension speed and oil content of each component in the bran through air selection, rolling and screening processes to achieve rice germ separation, but this method requires special equipment, and the product has high fat content and lipase activity, and is difficult to store. Related research mainly concentrated on the mid-1980s to around 2005, and there have been few related reports in the past two decades. The closely related patents include application numbers CN201710082763.9, CN202111546946.4 and CN202223604613.5. But in general, due to factors such as relatively low rice germ content, tight combination of bran and germ, and high oil content, the separation and preparation of rice germ generally has problems such as low efficiency, high energy consumption, complex equipment and processes, and unstable products. The separation and preparation of black rice germ has never been reported. Exploring and practicing new (black) rice germ preparation processes is of great significance to the high-quality development of the rice deep processing industry. Summary of the invention

[0006] In order to overcome the limitations of the traditional preparation method of rice germ described in the prior art and the shortcomings of the black rice germ preparation process, the object of the present invention is to provide a defatted black rice germ preparation process based on density flotation, and a low-polarity lipophilic solvent with suitable density is used to process (defatting and density flotation) a black rice bran germ mixture, and defatting, bran germ separation and anthocyanin retention are achieved simultaneously to prepare defatted black rice germ. The method is simple in steps, has good separation effect, high comprehensive recovery rate, and the solvent can be recycled and used, and the product instability problem caused by high oil content can be effectively avoided, and anthocyanins and enriched trace nutrients such as γ-aminobutyric acid can be effectively retained, which has positive significance for helping to realize the deep processing and high value utilization of black rice.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0009] (1) Hulling: Selecting plump, uniform, and moisture-appropriate black rice grains, removing the husks from the rice grains to obtain black rice brown rice;

[0010] (2) rice milling: grinding the black rice and brown rice obtained in step (1) to collect black rice bran containing black rice germs, i.e., a bran-germ mixture;

[0011] (3) degreasing: degreasing the bran-germ mixture obtained in step (2) with a low-polarity lipophilic solvent of suitable density, and controlling the solid-liquid ratio, degreasing time and stirring speed;

[0012] (4) density flotation: after defatting, the mixed system obtained in step (3) is allowed to stand for flotation for a period of time, so that the black rice germ and the black rice bran float on the solvent and sink under the solvent respectively due to their different densities;

[0013] (5) Sample recovery: collecting the black rice germ extract from the upper layer of the solvent, the black rice bran extract from the lower layer, and the rice bran oil extract from the solvent in step (4), and further rotary evaporating the solvent to obtain rice bran oil;

[0014] (6) Drying: The upper layer of black rice germ and the lower layer of black rice bran obtained in the solvent of step (5) are fully dried to obtain defatted black rice germ and defatted black rice bran.

[0015] Preferably, in step (1), the moisture content of the black rice is controlled at 13% to 16% w / w, and the hulling of the rice is performed by using a rice husker; the rice husker includes but is not limited to a rubber roller rice husker, a sand disk rice husker and a centrifugal rice husker;

[0016] Further preferably, in step (1), the moisture content of the black rice is controlled at 14% to 15% w / w, the rice husker is a MLGT20 type pressure roller rice husker, and the hulling rate should be ≥90%;

[0017] Preferably, in step (2), the milling is performed using a rice milling machine; the rice milling machine includes but is not limited to a rubbing type, a grinding type and a mixed type rice milling machine, and the milling degree of black rice and brown rice (yield of bran and germ mixture) is controlled to be 3% to 12% w / w;

[0018] Further preferably, the rice milling machine is a PCM-20A wiping rice milling machine (kitchen rice milling machine), and the grinding degree of black rice and brown rice (yield of bran and germ mixture) is controlled at 4% to 10% w / w; further at 4% to 7% w / w;

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

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

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

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

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

[0024] Preferably, in step (4), the static flotation time is 10 to 60 minutes, and the residual black rice germ in the black rice bran should be observed. If there is obvious residue, the system can be stirred again to further separate the two, and then further static flotation is performed;

[0025] Further preferably, in step (4), the static flotation time is 30 to 45 minutes;

[0026] Preferably, in step (5), the sample recovery method is: using a mesh colander (40-100 meshes) to filter and recover the upper black rice germ of the solvent, suction filtering (double-circle qualitative filter paper, -0.1 MPa) to recover the rice bran oil solvent extract and the lower black rice bran, and rotary evaporation (40-60° C., -0.1 MPa) to recover the solvent and rice bran oil;

[0027] Further preferably, the sample recovery method in step (5) is: using a mesh colander (60-100 meshes) to filter and recover the upper black rice germ of the solvent, suction filtering (double-circle qualitative filter paper, -0.1 MPa) to recover the rice bran oil solvent extract and the lower black rice bran, and rotary evaporation (40-50° C., -0.1 MPa) to recover the solvent and rice bran oil;

[0028] Preferably, in step (6), the drying step comprises: naturally evaporating the black rice germ in a fume hood until no obvious solvent remains, and then drying in an oven at 40 to 60° C. for 30 to 90 min;

[0029] Further preferably, in step (6), the drying step is: naturally volatilizing the black rice germ in a fume hood until no obvious solvent remains, and then placing it in an oven at 45-60° C. to dry 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 flotation process in step (4), it is collected in step (5), and after drying, a screening process is added to obtain defatted black rice germs, and the obtained small amount of black rice bran is combined with the black rice bran collected in step (5).

[0031] More preferably, the screening is through a 40-60 mesh sieve.

[0032] Defatted black rice germ, defatted black rice bran and rice bran oil prepared by the preparation process.

[0033] The defatted black rice germ yield using the above technical scheme is 3.63%-11.60% (relative to the bran germ mixture, the same below), the defatted black rice bran yield is 67.88%-80.45%, the rice bran oil yield is 12.17%-15.13%, the comprehensive recovery is 92.87%-99.51%, the solvent recovery is 68.33%-87.00%, and the defatted black rice germ yield, comprehensive recovery and solvent recovery are high;

[0034] The defatted black rice embryos prepared by the above-mentioned technical solution have a regular and uniform morphology, showing uniform black and white flat particles in the macroscopic view, and showing a visual appearance similar to the cross section of an oyster in the microscopic view ( Figure 3); In the embodiment (Table 3), the fat content of the defatted black rice embryo is 1.69% to 2.02%, and the lipase activity is 5.50 to 6.19 mg / g, which is significantly lower than that of black rice and black rice bran. 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 / gDW, which is significantly higher than that of black rice, indicating that the above-mentioned nutrients are enriched in the defatted black rice embryo, and the defatted black rice embryo has a higher nutritional value;

[0035] The technical principle of the present invention ( Figure 2 ): According to the difference in relative density of bran and germ, a low-polarity lipophilic solvent with density between the two is used to treat the bran-germ mixture. Driven by gravity, the black rice bran with high density sinks and the black rice germ with low density floats, thereby separating the bran and germ. At the same time, the low-polarity lipophilic solvent effectively extracts rice bran oil and retains anthocyanins, thereby improving the oxidative stability and nutritional value of the product.

[0036] Compared with the prior art, the present invention has the following advantages and effects:

[0037] (1) The present invention uses a solvent density flotation method to effectively separate black rice germ and rice bran under gravity drive, and simultaneously extracts rice bran oil (the main factor causing the unstable quality of rice bran and rice germ) and retains anthocyanins (the main functional factor of black rice and its processed products). The simultaneous degreasing, bran germ separation and anthocyanin retention based on the solvent density flotation method are significant beneficial effects not possessed by the prior art methods;

[0038] (2) The process steps of the present invention are simple, the bran-germ separation effect is good, the rice germ yield and the comprehensive recovery rate of the product are high, the solvent can be recycled, and defatted black rice bran and rice bran oil are obtained while obtaining defatted black rice germ, which is suitable for large-scale promotion. In a specific embodiment, the yield of defatted black rice germ is 3.63% to 11.60% (relative to the bran-germ mixture, the same below), the yield of defatted black rice bran is 67.88% to 80.45%, the yield of rice bran oil is 12.17% to 15.13%, 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 invention prepares defatted black rice germ with regular morphology, good stability (low fat content and lipase activity, not easy to become rancid), and high nutritional value (rich in functional factors such as polyphenols, anthocyanins and γ-aminobutyric acid), and black rice germ and its separation and preparation process are rarely reported;

[0040] (4) Compared with the traditional dry mechanical separation, the present invention requires simple instruments and tools, does not require customized special mechanical equipment, and can achieve synchronous degreasing; compared with (water) wet rinsing separation, the present invention can be particularly applied to black rice bran embryo separation without causing the loss of characteristic nutrient anthocyanin;

[0041] (5) The present invention provides a simple method for separating bran, germ and oil, which lays a good foundation for the process and raw materials for further enriching and preparing characteristic functional active factors of each part (such as anthocyanins / dietary fiber in black rice bran, vitamins / γ-aminobutyric acid in germ, oryzanol / phytosterols in rice bran oil, etc.), and is of great significance for promoting the deep processing and high-value utilization of black rice. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a process flow chart of the present invention;

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

[0044] Figure 3 These are the macroscopic and microscopic morphological images of defatted black rice germs obtained in Examples 1-6 (corresponding to (A)-(F)). DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the exemplary embodiments of the present invention will be described in more detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all, and the present invention can be implemented in various forms and should not be limited by the embodiments described here.

[0046] In the embodiments, the fat content is determined according to GB 5009.6-2016; the lipase activity is determined according to GB / T5523-2008; the anthocyanin content is determined by the pH differential method with reference to the method of Pang et al. (reference 1), and the anthocyanin content is expressed as milligram equivalents of cyanidin-3-O-glucoside (Cy 3-Glu) per gram of sample; the total phenol content is determined by the Folin-Ciocalteu method with reference to the method of Zhang (reference 2) and Hu Ting (reference 3) et al. with gallic acid as the standard, and the total phenol content is expressed as milligram equivalents of gallic acid contained in each gram of sample dry weight, i.e., mgGAE / g DW; the γ-aminobutyric acid content is determined by a colorimetric detection kit (Wuhan Elaruite Biotechnology Co., Ltd., catalog number: 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. Boundphenolic 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 MW, Zhang RF, Zhang FX, Liu RHPhenolic Profiles and Antioxidant Activity of Black Rice Bran of Different CommerciallyAvailable Varieties[J]. Journal of Agricultural and Food Chemistry, 2010, 58(13):7580-7587.

[0049] Reference 3: Hu Ting, Wang Xin, Geng Kezan, et al. Effects of ultrafine grinding on the composition and activity of black rice bran polyphenols [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 diagram of the present invention is as follows Figure 1 shown.

[0051] Example 1

[0052] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0053] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 15% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice brown rice;

[0054] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 7-point milling degree to mill the black rice and brown rice obtained in step (1), milling 320 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 7% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0055] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of dichloroethane, mix well, and then degrease at room temperature with magnetic stirring at 300 rpm for 1.0 h;

[0056] (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for 30 min, so that the black rice germ and the black rice bran float on the solvent and sink below the solvent, respectively;

[0057] (5) Sample recovery: The upper layer of black rice germ was filtered and recovered by a 60-mesh colander, 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), and the dichloroethane and rice bran oil were further recovered by rotary evaporation (50° C., -0.1 MPa);

[0058] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 50° C. oven for drying for 60 min to prepare defatted black rice germ and defatted black rice bran.

[0059] According to Example 1, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 5.63%, 80.45% and 13.43% respectively, the comprehensive recovery rate is 99.51%, and the recovery rate of the solvent (ethylene dichloride) is 87.00%.

[0060] The defatted black rice germ obtained by Example 1 has 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 / gDW, and a regular and uniform morphology ( Figure 3 (A)).

[0061] Example 2

[0062] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0063] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 14% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice and brown rice;

[0064] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 7-point milling degree to mill the black rice and brown rice obtained in step (1), milling 160 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 7% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0065] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of dichloromethane, mix well, and then degrease with magnetic stirring at 600 rpm at room temperature for 1.0 h;

[0066] (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for 30 min, so that the black rice germ and the black rice bran float on the solvent and sink below the solvent, respectively;

[0067] (5) Sample recovery: Use a 60-mesh screen colander to filter and recover the upper black rice germ of the solvent, vacuum filter (double-circle qualitative filter paper, -0.1 MPa) to recover the rice bran oil solvent extract (filtrate) and the lower black rice bran (filter cake), and further rotary evaporate (45° C., -0.1 MPa) to recover dichloromethane and rice bran oil;

[0068] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 50° C. oven for drying for 60 min to prepare defatted black rice germ and defatted black rice bran.

[0069] According to Example 2, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 10.42%, 75.23% and 12.17% respectively, the comprehensive recovery rate is 97.81%, and the recovery rate of solvent (dichloromethane) is 68.33%.

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

[0071] Example 3

[0072] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0073] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 14% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice and brown rice;

[0074] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 5-point milling degree to mill the black rice and brown rice obtained in step (1), milling 160 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 4% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0075] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of chloroform, mix well, and then degrease 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) is allowed to stand for 45 minutes to separate the black rice germ and black rice bran under gravity due to their different densities;

[0077] (5) Sample recovery: Use a 60-mesh screen colander to filter and recover the upper black rice germ (containing a small amount of black rice bran) of the solvent, vacuum filter (double-circle qualitative filter paper, -0.1 MPa) to recover the rice bran oil solvent extract (filtrate) and the lower black rice bran (filter cake), and further rotary evaporate (40° C., -0.1 MPa) to recover chloroform and rice bran oil;

[0078] (6) Drying and sieving: The black rice germ (containing a small amount of black rice bran) and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 45° C. oven for drying for 60 min, and a small amount of black rice bran (sieve undersize) is removed through a 40-mesh sieve to prepare defatted black rice germ (sieve retained portion) and defatted black rice bran.

[0079] It should be noted that due to the high density of chloroform (1.48 g / cm 3 ), during the density flotation process in step (4), a small amount of black rice bran floats on the upper layer of the solvent, which is filtered out in step (5), dried and sieved through a 40-mesh sieve to obtain defatted black rice germs, and the small amount of black rice bran is combined with the black rice bran recovered in step (5).

[0080] According to Example 3, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 11.33%, 70.04% and 12.90% respectively, the comprehensive recovery rate is 94.26%, and the recovery rate of the solvent (chloroform) is 79.30%.

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

[0082] Example 4

[0083] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0084] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 15% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice brown rice;

[0085] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 7-point milling degree to mill the black rice and brown rice obtained in step (1), milling 160 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 7% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0086] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of a mixed solvent of dichloroethane and dichloromethane in a volume ratio of 1:1, mix well, and degrease at room temperature with magnetic stirring at 450 rpm for 1.0 h;

[0087] (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for 45 minutes, so that the black rice germ and the black rice bran float on the solvent and sink below the solvent, respectively;

[0088] (5) Sample recovery: The upper layer of black rice germ was filtered and recovered by using a 100-mesh screen colander, 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), and the solvent and rice bran oil were further recovered by rotary evaporation (50° C., -0.1 MPa);

[0089] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 50° C. oven for drying for 60 min to prepare defatted black rice germ and defatted black rice bran.

[0090] According to Example 4, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 6.51%, 78.87% and 12.70% respectively, the comprehensive recovery rate is 98.08%, and the recovery rate of the solvent (mixed solvent of dichloroethane and dichloromethane) is 74.33%.

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

[0092] Example 5

[0093] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0094] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 14% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice and brown rice;

[0095] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 7-point milling degree to mill the black rice and brown rice obtained in step (1), milling 160 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 7% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0096] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of a mixed solvent of dichloroethane and chloroform in a volume ratio of 1:1, mix well, and degrease at room temperature with a magnetic stirring of 600 rpm for 45 min;

[0097] (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for 45 minutes, so that the black rice germ and the black rice bran float on the solvent and sink below the solvent, respectively;

[0098] (5) Sample recovery: The upper layer of black rice germ was filtered and recovered by a 60-mesh screen colander, 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), and the solvent and rice bran oil were further recovered by rotary evaporation (45° C., -0.1 MPa);

[0099] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 60° C. oven for drying for 30 min to prepare defatted black rice germ and defatted black rice bran.

[0100] According to Example 5, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 10.66%, 67.88% and 14.33% respectively, the comprehensive recovery rate is 92.87%, and the recovery rate of solvent (dichloroethane and chloroform) is 81.17%.

[0101] The defatted black rice germ obtained by Example 5 has a fat content of 1.82%, a lipase activity of 5.93 mg / g, an anthocyanin content of 4.12 mg / g, a γ-aminobutyric acid content of 21.93 mg / 100 g, a total phenol content of 9.60 mg GAE / gDW, and a regular and uniform morphology ( Figure 3 (E)).

[0102] Example 6

[0103] A process for preparing defatted black rice germ based on density flotation method comprises the following steps:

[0104] (1) Hulling: Preferably, plump, uniform black rice with a moisture content of 15% w / w is selected, and the rice husk is removed by using a MLGT20 type rubber roller rice husker, and the hulling rate is controlled to be 90% to obtain black rice brown rice;

[0105] (2) rice milling: using a PCM-20A rubbing rice milling machine to select a 7-point milling degree to mill the black rice and brown rice obtained in step (1), milling 320 g each time, controlling the milling degree (yield of bran-germ mixture) to be about 7% w / w, and collecting black rice bran containing black rice germs (bran-germ mixture);

[0106] (3) Degreasing: Weigh 10.00 g of the bran germ mixture obtained in step (2), add 100 mL of a mixed solvent of dichloromethane and chloroform in a volume ratio of 1:1, mix well, and degrease at room temperature with a magnetic stirring of 500 rpm for 60 min;

[0107] (4) Density flotation: After defatting, the mixed system obtained in step (3) is allowed to stand for 30 min, so that the black rice germ and the black rice bran float on the solvent and sink below the solvent, respectively;

[0108] (5) Sample recovery: The upper layer of black rice germ was filtered and recovered by a 60-mesh screen colander, 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), and the solvent and rice bran oil were further recovered by rotary evaporation (50° C., -0.1 MPa);

[0109] (6) Drying: The black rice germ and black rice bran obtained in step (5) are naturally evaporated in a fume hood until no obvious solvent remains, and then placed in a 50° C. oven for drying for 60 min to prepare defatted black rice germ and defatted black rice bran.

[0110] According to Example 6, the yields of defatted black rice germ, defatted black rice bran and rice bran oil are 11.33%, 71.09% and 15.13% respectively, the comprehensive recovery rate is 97.54%, and the recovery rate of solvent (dichloromethane and chloroform) is 76.00%.

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

[0112] Example 7

[0113] Density flotation solvent selection and density determination:

[0114] (1) Choice of solvent:

[0115] Accurately weigh 1.0g of black rice bran containing black rice germ (7 points grinding degree) and place it in a 15mL sample bottle (14 parts), add 10mL of petroleum ether, n-hexane, cyclohexane, carbon tetrachloride, ether, dichloromethane, dichloroethane, ethanol, ethyl acetate, isopropanol, chloroform, acetone, methanol, and water respectively, defatting with magnetic stirring at 600rpm at room temperature for 1.0h, let it stand for about 1.0h after defatting, and observe the phenomenon of the extraction system; then transfer all the extracts to a centrifuge tube, centrifuge at 8000rpm for 3.0min, and observe the phenomenon of the extract.

[0116] The results showed that the black rice germ floated on the upper layer of the dichloromethane, dichloroethane and chloroform extraction systems, the bran-germ mixture of the carbon tetrachloride extraction system floated on the solvent, and the bran-germ mixture of the other solvent extraction systems sank below the solvent; after centrifugation, it was found that the extracts of petroleum ether, n-hexane, cyclohexane, carbon tetrachloride, ether, dichloromethane, dichloroethane, ethyl acetate, chloroform and acetone extraction systems had no obvious purple or red color, and the ethanol, isopropanol, methanol and water extracts showed the typical red or purple-black color of anthocyanins. The above results suggest that dichloromethane, dichloroethane and chloroform can be used as solvents for separating bran and germ, and can retain the characteristic nutrient anthocyanins.

[0117] (2) Determination of density of flotation solvent:

[0118] In order to determine the appropriate solvent density for bran and germ separation, n-hexane and carbon tetrachloride were mixed in a certain proportion to prepare densities of 1.10-1.50 g / cm 3 The process was then carried out according to the conditions and parameters described in Example 2, except that dichloromethane was replaced by the above-mentioned gradient density solvent, and a sieving step as described in step (6) of Example 3 was added when necessary. The bran germ flotation separation effect of different density solvents was evaluated by taking the yield of defatted black rice germ as an evaluation index. The results are shown in Table 1.

[0119] Table 1 The yield of defatted black rice germ by flotation of solvents with different densities

[0120]

[0121] The results show (Table 1) that the density range is 1.20~1.50g / cm 3 The solvents can achieve a certain effect of separating bran and germ, the yield of defatted black rice germ is between 3.63% and 11.60%, and the solvent density is 1.30, 1.35 and 1.40 g / cm 3 The separation effect of bran and germ is best when the solvent density is lower than 1.30g / cm 3 When the black rice germs are suspended or sink, the solvent density is lower than 1.20 g / cm 3When the bran-germ mixture is completely sunk to the lower layer of the solvent, no black rice germ can be obtained; accordingly, the solvent density is higher than 1.40 g / cm 3 When the black rice bran has a tendency to suspend or float, the black rice germs collected subsequently are mixed with a certain amount of black rice bran, and a sieving step as described in step (6) of Example 3 needs to be added. 3 The dichloromethane was tested according to the conditions and parameters described in Example 1, and the yield of defatted black rice germ was 10.68%. The above results show that the density of the flotation solvent for separation of bran germ should be between 1.20 and 1.50 g / cm 3 , preferably with a density of 1.30 to 1.40 g / cm 3 , and the preferred density is 1.325 g / cm 3 of dichloromethane.

[0122] Comparative Example 1

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

[0124] Comparative Example 2

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

[0126] Comparative Example 3

[0127] The difference from Example 2 is that the grinding degree (yield of bran and germ mixture) in step (2) is controlled at 14.80%.

[0128] According to the process described in Examples 1-6 and Comparative Examples 1-3, the yield of defatted black rice germ, 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 Comparison of bran-embryo separation effect data of embodiments and comparative examples

[0130]

[0131] As can be seen from Table 2, according to the design spirit of the present invention, Examples 1-6 can all achieve separation of bran germs to obtain defatted black rice germs, especially when the solvent density is between 1.30 and 1.50 g / cm 3When (Examples 2, 3, 5, 6), the complete black rice germ in the bran-germ mixture can be almost completely recovered, and the yield can reach more than 10%. Comparative Examples 1 and 2 use n-hexane and methanol to replace the solvent described in Example 2 respectively, as a result, the black rice germs all sink under the solvent, and the bran-germ separation cannot be achieved, and the color of the methanol defatting flotation system extract is purple-black, and the yield of rice bran oil (solvent extract rotary evaporation residue) is significantly higher, indicating that a large amount of anthocyanins and other substances are extracted, which will lead to the loss of nutrients in the product (defatted rice bran); Comparative Example 3 uses a bran-germ mixture with a higher grinding degree, and its defatted black rice germ yield is significantly lower than that of Example 2, which may be because the complete rice germ structure is destroyed when the grinding degree is higher, resulting in a reduction in the amount of rice germ floating during the density flotation process. The comprehensive recovery rate of the products of Examples 1-6 can 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 stability and nutritional index data of defatted black rice germ, such as 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 defatted black rice germ prepared in Example 3 and its control sample

[0134]

[0135] As can be seen from Table 3, according to the design spirit of the present invention, the fat content and lipase activity of the defatted black rice germ obtained in Examples 1-6 are significantly lower than those of black rice and black rice bran. Lipase-mediated lipid hydrolysis is an important factor causing oxidative rancidity and quality deterioration of processed cereal products. Therefore, the defatted black rice germ obtained by the process of the present invention has better oxidative stability than black rice and black rice bran, which is conducive to long-term maintenance; in terms of nutritional indicators, the anthocyanin, γ-aminobutyric acid content and total phenol content of the defatted black rice germ are all significantly improved compared to black rice (since anthocyanins and phenols are mainly present in the cortex, the content of these two components in black rice bran is still higher than that of the defatted black rice germ). The γ-aminobutyric acid content of the defatted black rice germ is also greatly improved compared to the black rice bran, because γ-aminobutyric acid is mainly present in the rice germ, and is a water-soluble nutrient element. It is less dissolved during solvent defatting and density flotation, and is better retained in the defatted black rice germ. The above results show that the defatted black rice germ obtained by the process of the present invention has good stability and high nutritional value.

[0136] In summary, the present invention provides a simple, efficient and multi-benefit defatted black rice germ preparation process based on the density flotation principle, which realizes the separation of bran and germ while effectively avoiding the product stability problem caused by fat and lipase, retains the active factor anthocyanin, and obtains defatted black rice germ with high stability (low fat content and lipase activity) and high nutritional value (rich in polyphenols, anthocyanins and γ-aminobutyric acid), which expands the technical experience for the deep processing and high-value utilization of rice, especially black rice.

[0137] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A process for preparing defatted black rice germ based on density flotation method, characterized in that: The following steps are involved: (1) Hulling: Select full, uniform black rice with appropriate moisture content, remove the rice husk, and obtain black rice brown rice; (2) rice milling: grinding the black rice and brown rice obtained in step (1) to collect black rice bran containing black rice germs, i.e., a bran-germ mixture; (3) degreasing: degreasing the bran-germ mixture obtained in step (2) with a low-polarity lipophilic solvent of suitable density, controlling the solid-liquid ratio, degreasing time and stirring speed; (4) density flotation: after defatting, the mixed system obtained in step (3) is allowed to stand for flotation for a period of time, so that the black rice germ and the black rice bran float on the solvent and sink under the solvent respectively due to their different densities; (5) Sample recovery: collecting the black rice germ extract from the upper layer of the solvent, the black rice bran extract from the lower layer, and the rice bran oil extract from step (4), and further rotary evaporating the solvent to obtain rice bran oil; (6) Drying: The upper layer of black rice germ and the lower layer of black rice bran obtained in the solvent of step (5) are fully dried to obtain defatted black rice germ and defatted black rice bran.

2. The defatted black rice germ preparation process based on density flotation method according to claim 1, characterized in that: In step (3), the density of the low-polarity lipophilic solvent is between the density of black rice bran and black rice germ, the solid-liquid ratio is 1g:50mL to 1g:5mL, the degreasing time is 10 to 90min, and the stirring speed is 100 to 1000rpm.

3. The defatted black rice germ preparation process based on density flotation method 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 / cm 3 The material-liquid ratio is 1 g:10 mL, the degreasing time is 45 to 60 min, and the stirring speed is 300 to 600 rpm.

4. The defatted black rice germ preparation process based on density flotation method according to claim 1, characterized in that: In step (3), the low polarity lipophilic solvent is one or a mixed solvent of any combination of dichloromethane, dichloroethane and chloroform, or a solvent having a density of 1.20 to 1.50 g / cm 3 A mixed solvent of n-hexane and carbon tetrachloride.

5. The process for preparing defatted black rice germ based on density flotation method according to any one of claims 1 to 4, 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-germ mixture is controlled to be between 3% and 12% w / w.

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

7. The process for preparing defatted black rice germ based on density flotation method according to any one of claims 1 to 4, characterized in that: In step (4), the time of standing flotation is 10 to 60 minutes, and the residual black rice germ in the black rice bran should be observed. If there is obvious residue, the system is stirred again to further separate the two, and then further standing flotation is performed; In step (5), the rotary evaporation conditions are 40-60° C., −0.1 MPa; In step (6), the drying step is: naturally volatilizing the black rice germ until no obvious solvent remains, and then placing it at 40-60° C. and drying for 30-90 minutes.

8. The process for preparing defatted black rice germ based on density flotation method according to claim 7, characterized in that: In step (4), the static flotation time is 30 to 45 minutes; In step (5), the rotary evaporation conditions are 40-50° C., −0.1 MPa; In step (6), the drying step is: naturally volatilizing the black rice germ until no obvious solvent remains, and then placing it at 45-60° C. and drying for 30-60 minutes.

9. The process for preparing defatted black rice germ based on density flotation method according to any one of claims 1 to 4, characterized in that: In step (6), if a small amount of black rice bran floats on the upper layer of the solvent during the density flotation process in step (4), it is collected together in step (5), and after drying, a screening process is added to obtain defatted black rice germs, and the obtained small amount of black rice bran is combined with the black rice bran collected in step (5).

10. Defatted black rice germ, defatted black rice bran and rice bran oil prepared by the preparation process according to any one of claims 1 to 9.

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