Method for preparing rice bran powder by utilizing sectional type steam explosion technology

Abstract

The invention discloses a method for preparing rice bran powder by using a sectional type steam explosion technology, which comprises the following steps: (1) removing impurities from fresh rice bran, immediately spraying a color fixative on the rice bran, uniformly stirring, adding into a steam explosion machine, and carrying out two-section type steam explosion treatment to obtain wet rice bran powder; and (2) drying the wet rice bran powder obtained in the step (1) until the water content is below 10% to obtain the rice bran powder, the steam explosion treatment conditions in the step (1) are as follows: the first section is 0.6 MPalt; the steam pressure is smaller than or equal to 0.8 MPa, and the pressure maintaining time is 1-2 min; in the second stage, the steam pressure is larger than or equal to 0.3 MPa and smaller than or equal to 0.6 MPa, the heat preservation range is 135-160 DEG C, and the pressure maintaining time is 2-5 min. Compared with the prior art, the preparation method has the advantages that the stability of the rice bran can be effectively improved, the taste, sensory characteristics and digestibility of the rice bran are improved, the operation time is short, and the energy consumption is low.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a method for preparing rice bran powder by utilizing a segmented steam explosion technology. Background Art

[0002] Rice is one of the main food crops in my country. According to statistics, in 2020, my country's rice production exceeded 210 million tons, and its main by-product, rice bran, produced more than 12 million tons per year. Rice bran is one of the most nutritious parts of rice, containing 25-40% dietary fiber, 10-20% lipids (75-80% of which are unsaturated fatty acids), 11-17% protein, and a large amount of minerals, vitamins and other bioactive substances, including polyphenols, total flavonoids, γ-oryzanol, squalene, etc. However, due to the presence of fat and lipoxygenase, rice bran will quickly become rancid after rice milling, so the lipoxygenase must be immediately passivated through a stabilization process.

[0003] At present, common stabilization methods are extrusion and high-temperature enzyme inactivation. The extrusion method mainly inactivates enzymes through high temperature, high pressure and high shear during the extrusion process. It has the advantages of rapid processing, short time consumption and is suitable for large-scale production. However, due to the high temperature during the extrusion process, the nutritional loss of rice bran is serious, and due to the high pressure, the rice bran is severely compacted, has a high hardness, poor taste and poor edibility. In addition, the rice bran has a high content of insoluble dietary fiber and is not easy to digest by the human body. The above factors have led to the fact that extruded stabilized rice bran is often used as livestock feed and is not easily processed into food for human absorption. High temperature and wet heat enzyme inactivation combined with color preservatives can greatly improve the storage stability of rice bran and maintain the original color of rice bran, but the subsequent wet milling and drying processes are complicated, time-consuming and energy-intensive.

[0004] Steam explosion is a technology that uses the steam ejection principle to pre-treat materials through an explosion process. Although steam explosion technology has certain potential in the treatment of rice bran stability, the current steam explosion technology often requires the assistance of subsequent crushing treatment technology to achieve the ideal stabilization effect. This not only increases the processing time, but also makes the process operation more complicated and energy consumption increases accordingly. Therefore, it is particularly important to explore a more efficient, energy-saving and stabilization method that can maintain the nutritional value of rice bran. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the present invention aims to provide a stabilization and ultrafine grinding treatment method that is efficient, energy-saving and can maintain the nutritional value of rice bran, so as to overcome the defects of serious nutritional loss, long processing time, high energy consumption and complex subsequent processes in the stabilization process of rice bran in the prior art. By optimizing the steam explosion treatment technology, the stabilization of rice bran is achieved, and its sensory quality and nutritional value are improved at the same time, providing a new way for the deep processing and utilization of rice bran. The present invention uses steam explosion treatment to quickly penetrate steam molecules into the interior of plant tissues, high-temperature passivation of the activity of quality fission enzymes, and secondly, the steam is released instantly, so that the internal energy of the steam is converted into mechanical energy and acts on the cell layers of biomass tissues, thereby physically decomposing the raw materials with less energy. Two-stage steam explosion can simultaneously achieve ultrafine grinding treatment and rice bran stabilization, and the subsequent drying time is short, the whole set of treatment time is short, the energy consumption is low, and the nutrient release rate is high.

[0006] To achieve the above object, the present invention provides a method for preparing rice bran powder using segmented steam explosion technology, comprising the following steps:

[0007] (1) after the fresh rice bran impurities removal, immediately spray the rice bran with a color retaining agent and stir, then add it into a steam explosion machine, carry out a two-stage steam explosion process, and obtain the rice bran wet powder;

[0008] (2) drying the rice bran wet powder obtained in step (1) to a water content of less than 10% to obtain the rice bran powder;

[0009] The steam explosion treatment conditions in step (1) are: in the first stage, 0.6MPa<steam pressure≤0.8MPa, and the pressure maintenance time is 1-2min; in the second stage, 0.3MPa≤steam pressure≤0.6MPa, the insulation range is 135-160°C, and the pressure maintenance time is 2-5min.

[0010] Furthermore, the color protecting agent in step (1) is an organic acid solution with a concentration of 0.1-0.5wt%, and the citric acid concentration in the organic acid solution is ≥0.05wt%. The organic acid can be citric acid or a mixture of multiple acids including citric acid. When the organic acid is a mixture of multiple acids, as an example, the organic acid includes citric acid and at least one acid selected from malic acid, tartaric acid, acetic acid, and ascorbic acid.

[0011] Usually, the pH of the color protecting agent in the above ratio is 2.1-3.5.

[0012] According to a specific embodiment of the present invention, the pH of the color preservative is 2.1-2.5 and the concentration is 0.1-0.2 wt %. According to a specific embodiment of the present invention, the mass ratio of the rice bran to the color preservative is 2:1-3:1.

[0013] Preferably, the drying condition in step (2) is ≤ 60°C.

[0014] Compared with the prior art, the method for preparing rice bran powder of the present invention has the following advantages:

[0015] 1. The present invention is a new type of rice bran processing technology that integrates crushing and enzyme inactivation: utilizing the characteristics of steam explosion, a two-stage steam explosion method is adopted to firstly rapidly penetrate steam molecules into the plant tissue, greatly reduce the particle size of rice bran, and inactivate part of lipase. Secondly, the rice bran is subjected to steam explosion treatment again. Since the particle size is greatly reduced, high-temperature and high-humidity steam can more easily and evenly penetrate into all parts of the rice bran plant structure, and the activity of lipase can be inactivated according to the target requirements. At the same time, the particle size of rice bran will be further reduced, and the rice bran will not produce adverse phenomena such as browning due to the overheating effect, which promotes the release of active ingredients and improves the edibility of rice bran and the bioavailability of active ingredients.

[0016] 2. The present invention does not require a subsequent crushing process to assist steam explosion, and the two-stage steam explosion has low energy consumption, short operation time, and high nutrient release rate.

[0017] 3. It is preferred to add less water (30-50wt%) during the whole process, which can significantly shorten the subsequent drying time and further reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Residual lipase activity in rice bran powder

[0019] Figure 2 Average particle size of rice bran powder

[0020] Figure 3 Rice bran pink color

[0021] Figure 4 Release amount and release enhancement rate of polyphenols and flavonoids from rice bran powder during simulated digestion

[0022] Table 1 Sensory evaluation criteria and scoring table for rice bran powder samples DETAILED DESCRIPTION

[0023] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0024] Example 1

[0025] (1) Fresh rice bran was cleaned of impurities, and the rice bran was immediately sprayed with a color preservative (citric acid: ascorbic acid: distilled water = 0.5:0.5:1000 by mass, pH = 2.5) and stirred evenly, wherein the mass ratio of rice bran: color preservative was 3:1.

[0026] (2) Steam explosion: the rice bran obtained in step (1) is added into a steam explosion machine, and the rice bran is subjected to steam explosion treatment to obtain rice bran wet powder; the steam explosion treatment conditions are: in the first stage, the steam pressure is 0.7 MPa, and the pressure maintenance time is 1 min; in the second stage, the steam pressure is 0.3 MPa, the temperature holding range is 135° C., and the pressure maintenance time is 2 min.

[0027] (3) Drying: Drying the rice bran wet powder obtained in step (2) at a drying temperature of 60° C. for 4 h until the water content is reduced to below 10%, and sieving through 200 mesh to obtain rice bran powder.

[0028] The rice bran powder obtained in Example 1 is recorded as S1.

[0029] Example 2

[0030] (1) Fresh rice bran is cleaned of impurities, and the rice bran is immediately sprayed with a color preservative (citric acid: distilled water = 1:1000 by mass, pH = 2.2) and stirred evenly, wherein the mass ratio of rice bran: color preservative is 2:1.

[0031] (2) Steam explosion: the rice bran obtained in step (1) is added into a steam explosion machine, and the rice bran is subjected to steam explosion treatment to obtain rice bran wet powder; the steam explosion treatment conditions are: in the first stage, the steam pressure is 0.7 MPa, and the pressure maintenance time is 1 min; in the second stage, the steam pressure is 0.6 MPa, the temperature holding range is 160° C., and the pressure maintenance time is 5 min.

[0032] (3) Drying: Drying the rice bran wet powder obtained in step (2) at a drying temperature of 60° C. for 3 h until the water content is reduced to below 10%, and sieving through 200 mesh to obtain rice bran powder.

[0033] The rice bran powder obtained in Example 2 is recorded as S2.

[0034] Example 3

[0035] (1) Fresh rice bran is cleaned of impurities, and the rice bran is immediately sprayed with a color preservative (citric acid: ascorbic acid: distilled water = 1:1:1000 by mass, pH = 2.1) and stirred evenly, wherein the mass ratio of rice bran: color preservative is 3:1.

[0036] (2) Steam explosion: the rice bran obtained in step (1) is added into a steam explosion machine, and the rice bran is subjected to steam explosion treatment to obtain rice bran wet powder; the steam explosion treatment conditions are: in the first stage, the steam pressure is 0.8 MPa, and the pressure maintenance time is 2 min; in the second stage, the steam pressure is 0.6 MPa, the temperature holding range is 160° C., and the pressure maintenance time is 5 min.

[0037] (3) Drying: Drying the rice bran wet powder obtained in step (2) at a drying temperature of 60° C. for 4 h until the water content is reduced to below 10%, and sieving through 200 mesh to obtain rice bran powder.

[0038] The rice bran powder obtained in Example 3 is recorded as S3.

[0039] Comparative Example

[0040] (1) Fresh rice bran was cleaned of impurities, and the rice bran was immediately sprayed with a color preservative (citric acid: ascorbic acid: distilled water = 0.5:0.5:1000 by mass, pH = 2.5) and stirred evenly, wherein the mass ratio of rice bran: color preservative was 2:1.

[0041] (2) steam explosion: adding the rice bran obtained in step (1) into a steam explosion machine, and performing steam explosion treatment on the rice bran to obtain rice bran wet powder; the steam explosion treatment conditions are: steam pressure of 0.8 MPa, pressure maintenance time of 2 min, to obtain rice bran powder;

[0042] (3) Drying: Drying the rice bran wet powder obtained in step (3) at a drying temperature of 60° C. for 4 h until the water content is reduced to below 10%, and sieving through 200 mesh to obtain rice bran powder.

[0043] The rice bran powder obtained in the comparative example is recorded as S4.

[0044] Performance test experiment:

[0045] The rice bran powder prepared in the examples and comparative examples was subjected to the following performance tests.

[0046] 1. Lipase activity

[0047] A 2.0 g rice bran powder sample was mixed with 10 mL PBS buffer (0.1 mol / L, pH 7.0) and ultrasonically shaken at 25°C for 40 min. After centrifugation, 0.2 mL of the supernatant was mixed with 0.2 mL of solution A and 3 mL of solution B to obtain a mixture. Solution A was prepared by dissolving 40 mg of p-nitrophenyl laurate in 12 mL of isopropanol, and solution B was prepared by dissolving 0.4 g of Triton X-100 and 0.1 g of gum arabic in 90 mL PBS (0.1 mol / L, pH 7.0). The mixture was shaken at 37°C for 20 min and then boiled for 5 min. After centrifugation at 9600 × g for 10 min, the absorbance of the supernatant was measured at 410 nm using a spectrophotometer. The blank control consisted of 0.2 mL of boiled supernatant, 0.2 mL of solution A and 3 mL of solution B. The residual lipase activity was expressed as the relative activity (%) relative to fresh rice bran. Figure 1As shown, the residual lipase activity of the rice bran powder prepared by the two-stage steam explosion technology in the embodiment is significantly reduced compared with the rice bran powder prepared by the one-stage steam explosion, thereby significantly improving the storage stability of the rice bran powder.

[0048] 2. Granularity

[0049] 1.0 g of rice bran powder sample was dispersed in 10 mL of distilled water and ultrasonically vibrated for 10 min. The particle size distribution of the rice bran sample was measured using a laser particle size analyzer and the corresponding particle size parameters were obtained. The Span value (average particle size) of the particle size distribution was determined according to the following formula:

[0050] Span=(D 90 -D 10 ) / D 50

[0051] Where D 10 , D 50 and D 90 These are the equivalent volume diameters at cumulative volumes of 10%, 50% and 90% respectively.

[0052] like Figure 2 As shown, the rice bran powder prepared in the embodiment and the comparative example has a good particle size distribution, and the average particle size reaches micron level.

[0053] 3. Color difference

[0054] The chromaticity values ​​of different rice bran powders were measured using a colorimeter. Before the measurement, the equipment was calibrated with a standard white calibration plate and a light trap, and E-CG0 was used as a blank control. Chromaticity is expressed in the form of CIE color parameters, L * is brightness, with a scale from black (0) to white (100); a * is redness (+) and greenness (-); b * is yellowness (+) and blueness (-). The total color difference ΔE is calculated as follows:

[0055]

[0056] Where:

[0057] L0, a0, b0——L of fresh rice bran * value, a * Value and b * value;

[0058] L * 、a * 、b * ——L of rice bran powder prepared in Example or Comparative Example * value, a * Value and b * value.

[0059] like Figure 3 As shown, the difference in the pink color of rice bran prepared in Example 3 is relatively large. The difference in the pink color of rice bran prepared in other examples and comparative examples is small. The reason may be that the second stage steam explosion in Example 3 adopts the maximum pressure, temperature and time, so that the degree of Maillard browning reaction is the most intense.

[0060] 4. Release rate of polyphenols and flavonoids from rice bran in an in vitro simulated digestion model

[0061] In vitro simulated digestion:

[0062] Gastric juice is prepared with 0.25g porcine pepsin, 0.5g NaCl, 1.8mL HCl and 250mL distilled water. Accurately weigh 1.0g rice bran powder and mix with 10mL gastric juice, place in a 37℃ water bath, and digest for 3h. After digestion, take 1.5mL digestion solution and add 0.14mL NaOH (40g / L) to terminate the digestion reaction. Centrifuge for 15min and take the supernatant to obtain gastric digestion solution.

[0063] Adjust the pH of 10.0g / L pancreatic enzyme solution to 7.5 with 0.1M NaHCO3 to obtain simulated intestinal fluid. Accurately weigh 1.0g rice bran powder and mix with 10ml intestinal fluid, and digest for 1h in a 37℃ water bath. Immediately after digestion, inactivate the enzyme in a 100℃ water bath for 5min. Centrifuge for 15min and aspirate the supernatant, which is the intestinal digestion fluid.

[0064] (1) Determination of free polyphenol content: Folin- The content of free polyphenols was determined by the method. Take 0.3 mL of 10-fold diluted gastric digestive juice and mix it with 2.25 mL of Folin phenol reagent (10%). After shaking for 5 minutes, add 2.25 mL of Na2CO3 (60 g / L). After reacting for 90 minutes at room temperature (25°C) in the dark, immediately measure the absorbance value at 760 nm. The standard curve was drawn based on the standard gallic acid solution, and the results were expressed as gallic acid equivalents (mg GAE / g DM) per 100 grams of dry matter.

[0065] The calculation formula of polyphenol release enhancement rate ΔR is:

[0066]

[0067] Where R0 is the polyphenol release of fresh rice bran, and R1 is the polyphenol release of rice bran powder.

[0068] (2) Determination of free flavonoid content: 0.5 mL of gastric digestive juice was mixed with 150 μL of NaNO2 (50 g / L), 150 μL of AlCl3 (100 g / L) and 3 mL of distilled water. After reacting at room temperature (25°C) for 10 min, 1 mL of NaOH (40 g / L) was added and the absorbance was measured at 510 nm. The content of free total flavonoids was expressed as catechin equivalent per 100 g of dry matter (mg catechin eq / 100 g DM). A standard curve was drawn based on the standard catechin solution to calculate the content of flavonoids in the digestive juice.

[0069] The calculation formula for the flavonoid release enhancement rate ΔR' is:

[0070]

[0071] Where R'0 is the flavonoid release of fresh rice bran, and R'1 is the flavonoid release of rice bran powder.

[0072] like Figure 4 As shown, compared with the comparative example, the rice bran powder prepared in the embodiment retains polyphenols and flavonoids to a greater extent, is more conducive to the retention of bioactive substances, and has better nutritional value of rice bran. Using intestinal digestive juice instead of gastric digestive juice to measure the free polyphenol content and free flavonoid content, similar results as above can be obtained.

[0073] 5. Sensory evaluation of rice bran

[0074] The evaluation members consisted of 9 persons. Under the premise of not affecting each other, the rice bran powder prepared in Examples 1-3 and the comparative example was subjected to sensory evaluation of color, smell and taste. The specific evaluation indicators are shown in Table 1.

[0075] Table 1 Sensory evaluation criteria and scoring table for rice bran powder samples

[0076]

[0077]

[0078] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing rice bran powder using segmented steam explosion technology, characterized in that: The method comprises the following steps: (1) after the fresh rice bran impurity removal, immediately spray the rice bran with a color retaining agent and stir, then add it into a steam explosion machine, carry out a two-stage steam explosion process, and obtain the rice bran wet powder; (2) drying the rice bran wet powder obtained in step (1) to a water content of less than 10% to obtain the rice bran powder; The steam explosion treatment conditions in step (1) are: in the first stage, 0.6MPa<steam pressure≤0.8MPa, and the pressure maintenance time is 1-2min; in the second stage, 0.3MPa≤steam pressure≤0.6MPa, the insulation range is 135-160°C, and the pressure maintenance time is 2-5min.

2. The method according to claim 1, characterized in that The color protecting agent in step (1) is an organic acid solution with a concentration of 0.1-0.5wt%, and the citric acid concentration in the organic acid solution is ≥0.05wt%.

3. The method according to claim 2, characterized in that The organic acid includes citric acid and at least one acid selected from malic acid, tartaric acid, acetic acid and ascorbic acid.

4. The method according to claim 2, characterized in that The pH of the color protecting agent is 2.1-3.

5.

5. The method according to claim 2, characterized in that The color protecting agent has a pH of 2.1-2.5 and a concentration of 0.1-0.2 wt %.

6. The method according to claim 1, characterized in that The mass ratio of the rice bran to the color preservative is 2:1-3:

1.

7. The method according to claim 1, characterized in that The drying condition in step (2) is ≤ 60°C.

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