Method for multi-stage extraction of dietary fibers in bean dregs

Abstract

The invention discloses a method for multi-stage extraction of dietary fibers in bean dregs, and belongs to the technical field of biomass material extraction. The method comprises the following steps: washing bean dregs with water and carrying out enzymolysis treatment to obtain enzymolysis bean dregs; dietary fibers are extracted from the enzymolysis bean dregs through alkaline leaching, leaching liquid obtained through alkaline leaching is settled through alcohol, soluble dietary fibers are obtained, and filter residues obtained through alkaline leaching are insoluble dietary fibers; the preparation method comprises the following steps: sequentially carrying out hydrothermal treatment and DES solvent treatment on insoluble dietary fibers to obtain nano cellulose; carrying out oxidation treatment on the nanocellulose to obtain oxidized nanocellulose; according to the method, soluble dietary fibers in the bean dregs can be extracted, and insoluble dietary fibers can be fully extracted and utilized to obtain polysaccharides and micro-nano cellulose with high additional value, so that agricultural and sideline product wastes are fully utilized, the processing additional value of the agricultural and sideline product wastes is improved, and the pollution to the environment is reduced.

Description

Technical Field

[0001] The invention relates to a method for extracting dietary fiber from bean dregs, in particular to a method for multi-stage extraction of dietary fiber from bean dregs, and belongs to the technical field of biomass material extraction. Background Art

[0002] Okara is a byproduct of soy products. It is a high-quality byproduct rich in various nutrients, such as dietary fiber (DF), polysaccharides, isoflavones, small molecule peptides, etc. Although okara has high nutritional value, it has high water content, strong beany smell, difficult storage and easy to deteriorate and spoil. Further processing requires a lot of cost, resulting in low comprehensive utilization rate and added value, causing waste of resources and environmental pollution. The dietary fiber content in okara is as high as 50-70%, which is composed of a small amount of soluble dietary fiber (about 10%) (Soluble dietary fiber, SDF) and a large amount of insoluble dietary fiber (about 90%) (Insoluble dietary fiber, IDF). Dietary fiber is a plant component and is the "seventh nutrient" after vitamins, water, fat, carbohydrates, protein and minerals. It has the function of balancing human nutrition, regulating body functions, and has significant therapeutic and preventive functions for constipation, diabetes and obesity. It is favored by people who care about health and weight loss. People's pursuit of high-quality dietary fiber has promoted the research and development of dietary fiber.

[0003] At present, a large number of experts and scholars have explored the extraction and utilization of SDF in soybean dregs. Acid method, alkali method, enzymatic method and physical method are often used to extract SDF from soybean dregs, and then applied to the food field, such as biscuits, ham sausage, baking and other processing, to enhance its nutritional value. IDF is mainly composed of cellulose, hemicellulose and lignin. When applied to the food field, it has a significant impact on the processing characteristics, sensory quality and stability of food, and is not suitable for direct application in the food processing field. At present, it is often modified by physical methods (such as ultrasound, homogenization, ball milling, etc.), chemical methods (acid hydrolysis, oxidation, etc.) and biological methods (cellulose enzymatic hydrolysis), but the modification effect is not good and the modification cost is high. Therefore, there are few studies on the extraction and application of IDF in soybean dregs. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide a method for multi-stage extraction of dietary fiber from bean dregs. The method uses bean dregs as raw materials, can not only extract its soluble dietary fiber, but also can fully extract and utilize its insoluble dietary fiber, and obtain polysaccharides and high value-added micro-nano cellulose in steps, thereby achieving full utilization of agricultural and sideline product waste, improving its processing added value, and reducing pollution to the environment.

[0005] In order to achieve the above technical purpose, the present invention provides a method for extracting dietary fiber from bean dregs in multiple stages, which comprises the following steps:

[0006] S1: washing and enzymolyzing the okara to obtain enzymolyzed okara;

[0007] S2: the enzymatically hydrolyzed bean dregs are subjected to alkali leaching to extract dietary fiber, the leaching solution obtained by the alkali leaching is subjected to alcohol precipitation to obtain soluble dietary fiber, and the filter residue obtained by the alkali leaching is insoluble dietary fiber;

[0008] S3: the insoluble dietary fiber is sequentially subjected to hydrothermal treatment and DES solvent treatment to obtain nanocellulose;

[0009] S4: The nanocellulose is subjected to oxidation treatment to obtain oxidized nanocellulose.

[0010] The multi-stage method for extracting dietary fiber from bean dregs of the present invention, first pre-treats the bean dregs, mainly removing the protein components therein, adopts water washing combined with enzymolysis, water washing can remove low molecular weight water-soluble proteins and water-soluble impurities, and other non-water-soluble proteins and impurities with larger molecular weights are treated with enzymolysis to fully remove the protein in the bean dregs, and first uses alkali leaching to extract dietary fiber on the basis of removing protein, and the alkali leaching method extracts mainly soluble dietary fiber (SDF), while insoluble dietary fiber (IDF) is first treated with hydrothermal method combined with DES solvent, and the hydrothermal treatment process can convert lignin and hemicellulose in IDF into polysaccharides for recovery, and the remaining is micro-nano cellulose, and micro-nano cellulose is hydrolyzed with DES solvent, and micron-scale nanocellulose can be broken into nano-scale cellulose, and these celluloses are oxidized to obtain oxidized nanocellulose. The method truly realizes the efficient extraction and resource utilization of dietary fiber in bean dregs, and the quality of the obtained soluble dietary fiber and oxidized nanocellulose is good, and the added value is high.

[0011] As a preferred solution, the enzyme used in the enzymatic hydrolysis treatment is a neutral protease. As a more preferred solution, the conditions of the enzymatic hydrolysis treatment are: the enzyme mass content in the system is 0.1-0.3%, the enzymatic hydrolysis temperature is 37-40° C., and the enzymatic hydrolysis time is 20-40 min. Under the preferred conditions, the efficient degradation and removal of protein can be promoted, which is beneficial to the subsequent extraction of dietary fiber.

[0012] As a preferred solution, the conditions for alkali leaching are: alkali solution mass concentration of 2% to 4%, leaching temperature of 60 to 90° C., and leaching time of 50 to 90 min. As a more preferred solution, the alkali solution includes NaOH solution and / or Na2CO3 solution. Under the preferred alkali leaching conditions, water-soluble dietary fiber can be fully dissolved and extracted.

[0013] As a preferred solution, the hydrothermal treatment conditions are: hydrothermal temperature of 150-200° C., and hydrothermal time of 30-60 min. Under the preferred hydrothermal conditions, impurities such as lignin and hemicellulose can be decomposed to produce polysaccharides, thereby improving the purity of the final extract nanocellulose.

[0014] As a preferred solution, the DES solvent is composed of choline chloride and oxalic acid in a ratio of 1:1.5 to 2:1. When the oxalic acid content is too high, crystal precipitates will appear, and when the oxalic acid content is too low, the nanocellulose extraction rate is low. The DES solvent is further preferably composed of choline chloride and oxalic acid in a ratio of 1:1.3 to 1:1.

[0015] As a more preferred solution, the conditions for DES solvent extraction are: extraction temperature is 90-100°C, and time is 10-30min. Under preferred conditions, micron-sized nanocellulose can be broken into nano-sized cellulose using DES solvent. If the temperature is too high, not only will the yield of micro-nano-sized fibers be greatly reduced, but also the final nanocellulose will be deeply oxidized, and the color of cellulose will change from white to black, which is unfavorable. If the time is too long, not only will the yield of micro-nano-sized fibers not be increased, but also the final nanocellulose will be deeply oxidized, and the color of cellulose will change from white to black, which is unfavorable.

[0016] As a preferred solution, the oxidation treatment uses hypochlorite solution as an oxidant, TEMPO and sodium bromide as catalysts; the oxidation treatment conditions are: the amount of TEMPO relative to micro-nano cellulose is 5-15 mg / 1g, the amount of TEMPO relative to micro-nano cellulose is 50-150 mg / 1g, the amount of hypochlorite solution relative to micro-nano cellulose is 0.5-1.5 mL / 1g, the pH is 8-11, and the oxidation treatment time is 10-20 minutes, wherein the effective chlorine mass content of the hypochlorite solution is not less than 10%. The oxidation treatment can remove impurities on the surface of nanocellulose and enrich its surface functional groups. TEMPO is used to treat the surface of the nanocellulose. In order to make the oxidation reaction more complete, an ultrasonic-assisted oxidation process is preferably used.

[0017] The alcohol precipitation process of the present invention adopts ethanol.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0019] The present invention obtains soluble dietary fiber, polysaccharide and micro-nano cellulose by multi-stage extraction of bean dregs, thereby realizing deep utilization of bean dregs and improving their processing added value. Compared with the extraction of lignocellulose, the lignin content in bean dregs is low, which reduces the lignin removal steps, reduces the discharge of waste liquid, and reduces the preparation cost. Compared with the traditional acid method, alkali method and ionic liquid method, the present invention adopts green, recyclable and cheap DES solution extraction, which causes less pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the insoluble dietary fiber prepared in Example 1 of the present invention.

[0021] Figure 2 This is a SEM image of the nanocellulose prepared in Example 1 of the present invention.

[0022] Figure 3 The macroscopic morphology of the nanocellulose prepared in Examples 1, 2 and 3 of the present invention.

[0023] Figure 4 This is a TEM image of the nanocellulose prepared in Example 1 of the present invention.

[0024] Figure 5 This is the TEM image of the oxidized nanocellulose prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0026] Example 1

[0027] Put the bean dregs into the filter cloth and rub them repeatedly until the water after rubbing is no longer turbid. After wringing out the water, put them into a beaker and add neutral protease at a ratio of 0.3wt%. Add deionized water in the beaker at a mass ratio of wet bean dregs: deionized water = 1:5, and perform enzymolysis under 40℃ ultrasonic conditions for 60min. In order to make the bean dregs contact with the protease more fully, stir them during the enzymolysis process. After enzymolysis, place the mixture in a 90℃ water bath to inactivate the protease at a treatment temperature of 90℃. After the treatment is completed, wash the enzymolysis bean dregs to remove impurities and protease. After filtering, place the enzymolysis bean dregs in a 90℃ oven to dry. After complete drying, use a grinder to crush them and pass through a 100-mesh sieve to obtain enzymolysis bean dregs powder. Weigh 3.0 g of enzymatically hydrolyzed bean dregs and place them in 100 mL of a 4% Na2CO3 solution. React in a 90°C water bath for 60 min. Centrifuge and use ethanol as a precipitant to precipitate the soluble dietary fiber in the supernatant. The volume ratio of the supernatant to ethanol is 1:1. The precipitation time is 8 h. Filter, wash and dry the precipitate to obtain the soluble dietary fiber. Wash the filter residue with deionized water until it is neutral to obtain the insoluble dietary fiber (see Figure 1 ).

[0028] Insoluble dietary fiber was used as raw material, and was first subjected to hydrothermal treatment at 180 °C for 1 h, and then the hydrothermally treated insoluble dietary fiber was hydrolyzed using DES solution (see Figure 3 Sample No. 4 in the middle), nanocellulose is obtained after degradation of insoluble dietary fiber (see Figure 2 and Figure 4 ), and treated it with a hydrothermal method to remove some impurities and promote subsequent hydrolysis into nanocellulose. The DES solution treatment conditions are: the molar ratio of choline chloride and oxalic acid in the DES solution is 2:1, the extraction temperature is 90°C, and the extraction time is 15min. Nanocellulose was successfully obtained. In order to enrich the surface functional groups of nanocellulose, it was oxidized. The specific operation process is: weigh 0.025g TEMPO and 0.25g NaBr and dissolve them in 500mL deionized water. After adding nanocellulose, 2mL NaClO solution (effective chlorine ≥ 10%) was added dropwise at 30°C, and the pH of the solution was controlled at about 10.0. After reacting for 2.5h, 10mL of anhydrous ethanol was added to terminate the reaction to obtain oxidized nanocellulose (see Figure 3 (sample No. 5).

[0029] The water holding capacity and swelling capacity of soluble dietary fiber were characterized, and it was found that the water holding capacity and swelling capacity of soluble dietary fiber obtained under this condition reached 12.28g / g and 10.11mL / g respectively. The morphology and structure of nanocellulose were characterized, and it was found that nano-scale cellulose was successfully obtained, with a cellulose yield (relative to insoluble dietary fiber) of about 42%, a cellulose diameter in the range of 2 to 5nm, and a length of several hundred microns.

[0030] Example 2

[0031] The only difference from Example 1 is that the extraction temperatures during the DES extraction of nanocellulose are different, being set at 100° C. and 110° C. respectively.

[0032] During the experiment, it was found that the extraction temperature and extraction time during the extraction of nanocellulose using DES solvent had a great influence on its extraction effect. The hydrothermal insoluble dietary fiber extracted in Implementation Case 1 was used as raw material to further compare the effects of extraction temperatures of 100°C and 110°C on the extraction effect of nanocellulose. The experimental results showed that when the extraction temperature increased from 90°C to 110°C, the nanocellulose extraction rate decreased from about 40% to about 20%. When the extraction temperature reached 110°C, the nanocellulose was deeply oxidized and the color of the cellulose changed from white to black. For details, see Figure 3 Sample No. 3 in .

[0033] Example 3

[0034] The only difference from Example 1 is that the extraction time of DES in the process of extracting nanocellulose is different, which is set to 30min and 45min respectively. The experimental results show that when the extraction time increases from 15min to 45min, the nanocellulose extraction rate does not change much, but it has a greater impact on the macroscopic morphology of nanocellulose. When the extraction time is too long, the nanocellulose undergoes more serious oxidation, resulting in a darker color of the sample. For details, see Figure 3 Therefore, the extraction time should not exceed 15 minutes during the experiment. Figure 3 Sample No. 1 in .

[0035] Example 4

[0036] The only difference from Example 1 is that the composition ratio of DES during the extraction of nanocellulose with DES is different, and the molar ratios of choline chloride to oxalic acid are 2:1, 1:1, 1:1.3, 1:1.5 and 1:2, respectively.

[0037] The experimental results show that when the oxalic acid content is too high (i.e., the molar ratio is 1:2), crystal precipitates will appear during the experiment, and when the content is too low, the nanocellulose extraction rate is low. The molar ratios of 1:1.3 and 1:1.5 were further optimized, and it was found that when the ratio is higher than 1:1.5, crystallization will occur, and it is more appropriate to control it below 1:1.3 during the preparation process.

Claims

1. A method for extracting dietary fiber from bean dregs in multiple stages, characterized in that: The steps include: S1: washing and enzymolyzing the okara to obtain enzymolyzed okara; S2: the enzymatically hydrolyzed bean dregs are subjected to alkali leaching to extract dietary fiber, the leaching solution obtained by the alkali leaching is subjected to alcohol precipitation to obtain soluble dietary fiber, and the filter residue obtained by the alkali leaching is insoluble dietary fiber; S3: the insoluble dietary fiber is sequentially subjected to hydrothermal treatment and DES solvent treatment to obtain nanocellulose; S4: The nanocellulose is subjected to oxidation treatment to obtain oxidized nanocellulose.

2. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1, characterized in that: The enzyme used in the enzymatic treatment is neutral protease.

3. A method for extracting dietary fiber from bean dregs in multiple stages according to claim 1 or 2, characterized in that: The conditions of the enzymatic hydrolysis treatment are: the enzyme mass content in the system is 0.1-0.3%, the enzymatic hydrolysis temperature is 37-40° C., and the enzymatic hydrolysis time is 20-40 min.

4. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1, characterized in that: The conditions for alkali leaching are: the mass concentration of alkali solution is 2% to 4%, the leaching temperature is 60 to 90° C., and the leaching time is 50 to 90 minutes.

5. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1 or 4, characterized in that: The alkali solution includes NaOH solution and / or Na2CO3 solution.

6. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1, characterized in that: The conditions of the hydrothermal treatment are: the hydrothermal temperature is 150-200° C., and the hydrothermal time is 30-60 min.

7. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1, characterized in that: The DES solvent is composed of choline chloride and oxalic acid in a ratio of 1:1.5 to 2:

1.

8. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1 or 7, characterized in that: The conditions of the DES solvent treatment are: temperature of 90-100° C. and time of 10-30 min.

9. The method for multi-stage extraction of dietary fiber from bean dregs according to claim 1, characterized in that: The oxidation treatment uses hypochlorite solution as an oxidant, and TEMPO and sodium bromide as catalysts; The oxidation treatment conditions are as follows: the amount of TEMPO relative to micro-nano cellulose is 5-15 mg / 1 g, the amount of TEMPO relative to micro-nano cellulose is 50-150 mg / 1 g, the amount of hypochlorite solution relative to micro-nano cellulose is 0.5-1.5 mL / 1 g, the pH is 8-11, and the oxidation treatment time is 10-20 min, wherein: The effective chlorine content of the hypochlorite solution shall not be less than 10% by mass.

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