Method for increasing polyphenol content in mung beans through solid state fermentation of aspergillus niger

Abstract

The invention relates to the technical field of microbial fermentation, in particular to a method for increasing the polyphenol content in mung beans through solid-state fermentation of aspergillus niger. According to the method, the mung beans are subjected to solid-state fermentation by adopting the aspergillus niger, the mung bean product with the polyphenol content remarkably increased and the antioxidant capacity remarkably enhanced is obtained, detection shows that the polyphenol content in the mung beans subjected to solid-state fermentation can reach 16-18 mg / g and is 4-5 times that of unfermented mung beans, the DPPH removal rate can reach 85-95%, compared with the prior art, the polyphenol content and the DPPH removal rate of the mung beans are remarkably increased, and the antioxidant capacity of the mung beans is remarkably improved. High-quality raw materials and technical support are provided for increasing the added value of mung bean resources and developing functional foods. According to the method, the whole grains of the mung beans are fermented, so that the nutritional value of the mung beans is comprehensively improved, and meanwhile, redundant wastes are not generated to cause resource waste.

Description

Technical Field

[0001] The invention relates to the technical field of microbial fermentation, in particular to a method for improving the polyphenol content in mung beans by solid-state fermentation of Aspergillus niger. Background Art

[0002] Mung bean (Vignaradiata), a cultivated species of the genus Vignaradiata of the Leguminosae family, is an annual herb with a cultivation history of more than 2,000 years in my country. As an important edible bean and traditional functional food, mung bean is rich in various nutrients and bioactive substances, and has antioxidant, antibacterial, anti-inflammatory, cardiovascular and cerebrovascular protection, cholesterol reduction, liver protection and other functions. Mung bean is rich in phenolic compounds, and the extraction and utilization of mung bean polyphenols have also been of great concern. At present, in order to improve the utilization rate of mung bean polyphenols, physical and mechanical treatment is often used to improve the extraction method and improve the extraction rate of mung bean polyphenols. Patent document CN105250356A discloses a method for extracting mung bean polyphenols by microwave and ultrasonic assisted solvent extraction, wherein mung bean is crushed, an acetone solution is added, and the extract is immersed under microwave and ultrasonic treatment conditions, and then the extract is subjected to rotary evaporation and freeze-drying to obtain mung bean polyphenols. This method improves the yield of mung bean polyphenols to a certain extent, but it causes great damage to other nutrients in mung beans, making it difficult to reuse them and easily causing waste of resources. In addition, this method fails to increase the polyphenols present in mung beans.

[0003] Research on improving the nutritional value of mung beans by microbial fermentation has mostly used fermented mung beans as auxiliary materials to make mung bean nutritious foods, such as mung bean nutritious bread, biscuits, soy milk, beverages, noodles, composite powder, mung bean paste, etc. Patent document CN105265894A discloses a mung bean fermented nutritious food and a method for making it. After soaking and boiling the mung beans, the mung beans are soaked and fermented for 12 to 15 hours, boiled and sterilized again, and root mold spore powder is accessed. After natural fermentation for 30 to 40 hours, nutritious mung bean food is obtained. This method boils the mung beans multiple times, which is easy to cause the loss of nutrients and the decline of biological activity. At present, the existing mung bean fermentation process is relatively complicated, the strains used are messy, and the physical and chemical properties of mung beans are studied more, while the increased mung bean polyphenol content is still at a low level, and the functional activity of mung beans has not been fully explored. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for increasing the polyphenol content in mung beans by solid-state fermentation using Aspergillus niger. The method provided by the present invention can increase the polyphenol content and antioxidant capacity of mung beans.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for increasing the polyphenol content in mung beans, comprising the following steps:

[0007] The mung beans are sequentially soaked, steamed in a water bath and sterilized by ultraviolet light to obtain sterilized mung beans;

[0008] The sterilized mung beans and Aspergillus niger seed liquid are mixed and solid-state fermented to obtain a fermentation product;

[0009] The mass volume ratio of the sterilized mung bean and the Aspergillus niger seed liquid is 100 g:7-9 mL; the number of viable bacteria in the Aspergillus niger seed liquid is 1×10 8 CFU / mL; the temperature of the solid-state fermentation is 25-27°C; the time of the solid-state fermentation is 10-12 days.

[0010] Preferably, the Aspergillus niger includes Aspergillus niger that can secrete endo-glucurase, exo-glucurase and glucosidase.

[0011] Preferably, the Aspergillus niger has a deposit number of CGMCC 3.3928.

[0012] Preferably, the mass volume ratio of the sterilized mung bean and Aspergillus niger seed liquid is 100 g:7-8 mL; the temperature of the solid-state fermentation is 26-27° C.; and the time of the solid-state fermentation is 10.5-11.5 d.

[0013] Preferably, the mass volume ratio of the sterilized mung bean and Aspergillus niger seed liquid is 100 g:7.5 mL; the temperature of the solid-state fermentation is 26.5° C.; and the time of the solid-state fermentation is 11 days.

[0014] Preferably, the water bath cooking time is 5 to 20 minutes.

[0015] Preferably, the ultraviolet sterilization time is 20 to 40 minutes.

[0016] Preferably, the thickness of the mung beans after water bath cooking during ultraviolet sterilization is 1 to 2 cm.

[0017] Preferably, the environmental humidity of the solid-state fermentation is 80% to 100%.

[0018] Preferably, the mung beans have no white core after soaking.

[0019] Beneficial effects:

[0020] 1. The present invention uses Aspergillus niger to carry out solid-state fermentation of mung beans to obtain a mung bean product with significantly improved polyphenol content and significantly enhanced antioxidant capacity, providing high-quality raw materials and technical support for improving the added value of mung bean resources and the development of functional foods.

[0021] 2. The present invention uses Aspergillus niger as the fermentation strain. The cellulase, xylanase, saccharifying enzyme, etc. produced by Aspergillus niger can decompose cellulose, pectin, lignin, etc. in mung beans, which can promote the release of polyphenols and solve the problem that beans are not easy to ripen and have poor taste.

[0022] 3. The present invention adopts a solid-state fermentation method, and its fermentation product is easy to extract, saving costs. And after testing, the polyphenol content in mung beans after solid-state fermentation can reach 16-18 mg / g, which is 4-5 times that of unfermented mung beans, and the DPPH clearance rate can reach 85-95%, which is significantly improved compared with the polyphenol content and DPPH clearance rate of mung beans in the prior art.

[0023] 4. The present invention adopts a sterilization method of water bath cooking plus ultraviolet irradiation to replace the traditional high-pressure sterilization method, which can achieve the purpose of sterilization and retain the nutritional components of mung beans to a greater extent.

[0024] 5. The present invention ferments the whole mung bean seeds, which comprehensively improves the nutritional value of the mung bean without generating excess waste and causing waste of resources.

[0025] 6. The present invention adopts response surface methodology to optimize fermentation conditions, determine the optimal fermentation conditions, ensure the scientificity and stability of the fermentation process, and provide guarantee and basis for the fermentation quality of mung beans.

[0026] 7. The fermentation method of the present invention is simple to operate. It only requires mixing the raw materials and the strains evenly, without the need for complicated processes and expensive equipment. During the fermentation period, it only requires ensuring the ambient temperature, without the need for other operations and human supervision, and has good practical value and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0028] Figure 1 This is the effect of fermentation time on mung bean polyphenol content and DPPH clearance rate;

[0029] Figure 2 This is the effect of fermentation temperature on mung bean polyphenol content and DPPH clearance rate;

[0030] Figure 3 This is the effect of inoculation amount on polyphenol content and DPPH clearance rate of mung bean;

[0031] Figure 4 The response surface diagram and contour diagram of mung bean polyphenol content under the interaction of fermentation time and fermentation temperature;

[0032] Figure 5The response surface diagram and contour diagram of mung bean polyphenol content under the interaction of fermentation time and inoculum amount;

[0033] Figure 6 The response surface diagram and contour diagram of mung bean polyphenol content under the interaction of fermentation temperature and inoculation amount;

[0034] Figure 7 The response surface diagram and contour diagram of mung bean DPPH free radical scavenging rate under the interaction of fermentation time and fermentation temperature;

[0035] Figure 8 The response surface diagram and contour diagram of mung bean DPPH free radical scavenging rate under the interaction of fermentation time and inoculum amount;

[0036] Fig. 9 The response surface diagram and contour diagram of mung bean DPPH free radical scavenging rate under the interaction of fermentation temperature and inoculation amount;

[0037] Fig.10 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0038] The present invention provides a method for increasing the polyphenol content in mung beans, comprising the following steps:

[0039] The mung beans are sequentially soaked, steamed and sterilized by ultraviolet light to obtain sterilized mung beans;

[0040] The sterilized mung beans and Aspergillus niger seed liquid are mixed and solid-state fermented to obtain a fermentation product;

[0041] The mass volume ratio of the sterilized mung bean and the Aspergillus niger seed liquid is 100 g:7-9 mL; the number of viable bacteria in the Aspergillus niger seed liquid is 1×10 8 CFU / mL; the temperature of the solid-state fermentation is 25-27°C; the time of the solid-state fermentation is 10-12 days.

[0042] The present invention preferably washes the mung beans to remove surface impurities and obtain washed mung beans.

[0043] After obtaining the washed mung beans, the present invention soaks the washed mung beans to obtain soaked mung beans. In the present invention, the soaking temperature is preferably 24-30°C, more preferably 25°C; the soaking time is preferably 6-14h, more preferably 12h; the mass ratio of mung beans to soaking water is preferably 1:2-5, more preferably 1:3; the soaked mung beans have no white core.

[0044] After obtaining the soaked mung beans, the present invention preferably screens the soaked mung beans to select the mung beans without skin, damaged, or eaten by insects to obtain screened mung beans.

[0045] After obtaining the screened mung beans, the present invention performs water bath steaming on the screened mung beans to obtain steamed mung beans. In the present invention, the water bath steaming time is preferably 5 to 20 minutes, more preferably 10 to 15 minutes, and more preferably 10 minutes.

[0046] After obtaining the steamed mung beans, the present invention sterilizes the steamed mung beans by ultraviolet light to obtain sterilized mung beans. In the present invention, the method of ultraviolet sterilization preferably includes: spreading the steamed mung beans on a sterilized iron plate with a thickness of 1 to 2 cm, placing the iron plate flat on a sterile operating table, and sterilizing by ultraviolet irradiation; the ultraviolet irradiation sterilization time is preferably 20 to 40 minutes, more preferably 30 minutes. The present invention adopts a sterilization method of water bath steaming plus ultraviolet irradiation to replace the traditional high-pressure sterilization method, which can achieve the purpose of sterilization and retain the nutritional components of mung beans to a greater extent.

[0047] After obtaining the sterilized mung beans, the present invention mixes the sterilized mung beans with Aspergillus niger seed liquid for solid-state fermentation to obtain a fermentation product. The mass volume ratio of the sterilized mung beans and the Aspergillus niger seed liquid of the present invention is 100 g: 7-9 mL, preferably 100 g: 7-8 mL, more preferably 100 g: 7.5 mL; the number of viable bacteria in the Aspergillus niger seed liquid is 1×10 8 CFU / mL; the temperature of the solid-state fermentation is 25-27°C, preferably 26-27°C, and more preferably 26.5°C; the time of the solid-state fermentation is 10-12d, preferably 10.5-11.5d, and more preferably 11d.

[0048] In the present invention, the Aspergillus niger preferably includes an Aspergillus niger that can secrete endo-glucosidase, exo-glucosidase and glucosidase; the Aspergillus niger used in the embodiment of the present invention is preferably purchased from the China General Microbiological Culture Collection Management Center, and its number is CGMCC 3.3928. The present invention uses Aspergillus niger as a fermentation strain. The cellulase, xylanase, saccharifying enzyme, etc. produced by Aspergillus niger can decompose cellulose, pectin, lignin, etc. in mung beans, which can promote the release of polyphenols and solve the problem that beans are not easy to ripen and have a poor taste.

[0049] In the present invention, the environmental humidity of the solid-state fermentation is preferably 80% to 100%.

[0050] The fermentation method of the present invention is simple to operate, and only requires the raw materials and the strains to be evenly mixed, without the need for complicated processes and expensive equipment; and during the fermentation period, only the environmental temperature and humidity need to be ensured, without the need for other operations and human supervision, and has good practical value and application prospects.

[0051] In order to further illustrate the present invention, a method for increasing the polyphenol content in mung bean by solid-state fermentation of Aspergillus niger provided by the present invention is described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] A method for improving the polyphenol content and DPPH clearance rate of mung beans by Aspergillus niger solid-state fermentation, specifically comprising the following steps:

[0054] (I) Raw material pretreatment

[0055] a. Cleaning: Wash the mung beans 2-3 times with tap water, then rinse once with purified water to remove impurities on the surface;

[0056] b. Soaking: Soak the mung beans in pure water at a temperature of 25°C for 12 hours, with a material-water mass ratio of 1:3, so that the mung beans are completely soaked without white core;

[0057] c. Screening: Select the mung bean seeds without skin, damage or insects;

[0058] d. Steaming: Steam the screened mung beans in a water bath for 10 minutes;

[0059] e. Sterilization: Spread the cooked mung beans on a sterilized iron plate with a thickness of 1.5 cm, place the iron plate flat on a sterile operating table, and sterilize under ultraviolet irradiation for 30 minutes;

[0060] (II) Seed solution preparation

[0061] a. Activation of strains: Inoculate freeze-dried powder of Aspergillus niger (deposit number CGMCC 3.3928) into Czapek's solid slant medium and culture at 28°C for 5 days. Pick a piece of Aspergillus niger block and inoculate it into a new Czapek's solid slant medium for passage once; the formula of the Czapek's solid medium is: sucrose 30.0g, NaNO3 3.0g, MgSO4·7H2O 0.5g, KCI 0.5g, FeSO4·4H2O 0.5g, K2HPO4 1.0g, agar 15.0g and distilled water 1.0L, pH 6.0-6.5;

[0062] b. Expansion culture: Pick two activated mycelium blocks and transfer them to new Czapek's solid slant medium. Culture them at 28°C for 6 days until Aspergillus niger grows black mature spores.

[0063] c. Rinse: Use physiological saline solution to repeatedly blow the mycelium surface to rinse the spores. Pour the rinsed spore suspension into a sterilized conical flask to obtain a spore suspension. Adjust the OD of the spore suspension. 600 =1.8;

[0064] d. Filtration: Add glass beads to the conical flask containing the spore suspension, seal the flask and place it in a shaker at 130 to 150 r / min for 30 min, filter the spore suspension with sterilized gauze to obtain the seed solution;

[0065] e. Number of viable bacteria: dilute the seed solution by 10 7 Then, take 0.1 mL and drop it on the surface of Czapek's solid medium, spread it evenly with a coating stick, and incubate it at 28°C for 3 days before checking the number of bacteria. 8 CFU / mL; in the above scheme, the sterilization conditions of the conical flask, iron plate, culture medium, glass beads, gauze and eluent are all: sterilization in a high pressure sterilizer at 121°C for 15 min.

[0066] (III) Solid-state fermentation

[0067] a. Single factor experiment

[0068] Taking fermentation time, fermentation temperature and inoculation amount as single factor variables, their effects on the polyphenol content and DPPH removal rate of fermented mung beans were investigated. 50g sterilized wet mung beans were weighed in each experiment, and the specific settings were as follows:

[0069] 1) The fermentation temperature was fixed at 28°C, the inoculation volume was 9 mL / 100 g, and the fermentation was carried out for 2 days, 4 days, 6 days, 8 days, 10 days, and 12 days respectively;

[0070] 2) The fermentation time was fixed at 6 days, the inoculation amount was 9 mL / 100 g, and the fermentation temperature was controlled at 24°C, 26°C, 28°C, 30°C, 32°C, and 34°C respectively;

[0071] 3) The fermentation time was fixed at 6 d and the fermentation temperature was 28°C. The inoculum size was controlled at 3%, 6%, 9%, 12%, 15% and 18% (i.e. 18 mL / 100 g) respectively.

[0072] b. Index determination

[0073] Solid-state fermentation was carried out according to the set single-factor test. After fermentation, the mung beans were placed in a 45°C oven and dried to constant weight, crushed through a 60-mesh sieve, and stored in a refrigerator at 4°C for later use. The polyphenol content and DPPH scavenging rate of the fermented mung beans were determined.

[0074] 1) Polyphenol extraction method: accurately weigh 5.0 g of fermented mung bean sample, add 50 mL of anhydrous ethanol solution with a volume fraction of 80%, perform ultrasonic extraction for 2 h, centrifuge at 4000 r / min for 20 min, take the supernatant, and place it in a vacuum drying oven to prevent oxidation. Extract the precipitate again using the same method, mix the supernatants after two centrifugations, concentrate the supernatant to about 5 mL using a rotary evaporator, and make up to 15 mL with anhydrous ethanol to obtain the mung bean polyphenol extract, which is stored in a refrigerator at -20°C for later use.

[0075] 2) Determination of polyphenol content: Use the Folin phenol colorimetry to draw a standard curve, prepare a 0.1 mg / mL gallic acid standard solution, take 0.2, 0.4, 0.6, 0.8, 1 mL of the standard solution and place it in a test tube, add deionized water to make up to 1 mL, take 0.1 mL of the sample solution, add 0.1 mL of Folin phenol and 0.4 mL of 15% Na2CO3 solution, and dilute to 1 mL with water. After mixing evenly, keep it in the dark for 1 hour, centrifuge and take the supernatant, and measure the absorbance at a wavelength of 765 min. After diluting the mung bean polyphenol extract 8 times, measure the absorbance according to the standard curve method, and the polyphenol content is measured in gallic acid equivalent (mgGAB / g).

[0076] 3) Determination of DPPPH clearance rate: 1 mL of mung bean polyphenol extract and 4 mL of DPPH (OD 517 =0.7) solution, shake vigorously, and place in the dark for 30 minutes after shaking. The absorbance is recorded at a wavelength of 517nm using an enzyme marker. The calculation formula for DPPH free radical scavenging ability is shown in Formula I:

[0077]

[0078] In formula I: A1 is the absorbance of the background group, A2 is the absorbance of the sample group, and A3 is the absorbance of the blank group.

[0079] c. Single factor test results

[0080] The results of each single factor test are as follows Figures 1 to 3 As shown, the results are: the optimal fermentation time is 10d, the optimal fermentation temperature is 26℃; the optimal inoculation amount is 9mL / 100g.

[0081] d. Response surface optimization

[0082] On the basis of the single factor experiment, a response surface experiment was designed, with polyphenol content and DPPH removal rate as response values, fermentation time (A), fermentation temperature (B), and inoculation size (C) as independent variables, and three levels (0, ±1) selected. The experimental design factors and levels are shown in Table 1.

[0083] Table 1. Design of experimental factor levels

[0084]

[0085] e. Determination of response surface experimental indicators

[0086] Design Expert 13 was used to establish a model to optimize the solid-state fermentation process of mung bean by Aspergillus niger. The polyphenol content and DPPH clearance rate of different experimental groups were determined according to the above-mentioned determination method. The Box-Behnken experimental design and experimental results are shown in Table 2.

[0087] Table 2. Content of each index in response surface test

[0088]

[0089]

[0090] f. Response surface test results

[0091] Design Expert 13 software was used to perform polynomial fitting regression on the experimental results, and the regression equation was obtained:

[0092] 1) Y polyphenol content = 17.29 + 1.52A + 0.12B - 0.1825C - 7.5 × 10- 3 AB-0.3075AC-0.0125BC-1.77A2-0.1793B2-0.3392C2. The variance analysis of this model is shown in Table 3.

[0093] Table 3 Model ANOVA

[0094] project sum of squares Degrees of Freedom Mean Square F-number Significant level Model 33.46 9 3.72 109.53 <0.0001 A-Fermentation time 18.36 1 18.36 540.92 <0.0001 B-Fermentation temperature 0.1152 1 0.1152 3.39 0.1080 C-Inoculation amount 0.2665 1 0.2665 7.85 0.0265 AB 0.0002 1 0.0002 0.0066 0.9374 AC 0.3782 1 0.3782 11.14 0.0125 BC 0.0006 1 0.0006 0.0184 0.8959 A2 13.18 1 13.18 388.27 <0.0001 B2 0.1353 1 0.1353 3.99 0.0861 C2 0.4846 1 0.4846 14.28 0.0069 Residual 0.2376 7 0.0339 / / Lack of Fit 0.1975 3 0.0658 6.56 0.0503 Pure Error 0.0401 4 0.0100 / / Total difference 33.70 16 / / /

[0095] Note: P<0.05 indicates significant difference, P<0.01 indicates extremely significant difference.

[0096] 2) Y DPPH Clearance rate = 94.564 + 4.70125A + 0.3363B - 1.455C - 1.385AB - 0.6375AC - 1.7175BC - 1.682A2 - 1.902B2 - 5.4245C2. The variance analysis of this model is shown in Table 4.

[0097] Table 4 Model ANOVA

[0098]

[0099]

[0100] Note: P<0.05 indicated significant difference, P<0.01 indicated extremely significant difference.

[0101] From Table 3, we can see that the regression equation Y 多酚含量 The regression equation Y DPPH清除率 The results showed that the binomial equation in the experimental model was more consistent with the actual fermentation situation, reflecting that the fermentation time, fermentation temperature and inoculation amount had a significant effect on the interaction of polyphenol content and DPPH clearance rate.

[0102] According to equation Y 多酚含量 The response surface and contour lines of the model are obtained, such as Figures 4 to 6 As shown. Figures 4 to 6 It can be seen that fermentation time, fermentation temperature and inoculation amount have significant effects on the content of mung bean polyphenols. DPPH清除率 The response surface and contour lines of the model are obtained, such as Figures 7 to 9 As shown. Figures 7 to 9 It can be seen that fermentation time, fermentation temperature and inoculum amount have a significant effect on the DPPH free radical scavenging rate.

[0103] The equation was solved by Design Expert software, and the optimal extraction process was obtained as follows: fermentation time 10.94d, fermentation temperature 26.69℃, inoculation amount 7.53%. Under this condition, the content of mung bean polyphenols was 17.707mg / g, and the DPPH clearance rate was 95.554%. Considering the actual operation and for the convenience of the experiment, the fermentation parameters were adjusted on this basis, and the optimal fermentation process conditions were determined to be inoculation amount 7.5mL / 100g, fermentation temperature 26.5℃, and fermentation time 11d.

[0104] Example 2 Fermentation agent comparison experiment

[0105] For further verifying the synergistic effect between mung bean and the black aspergillus fermentation agent, according to the optimal fermentation condition determined in Example 1, respectively adopt plant lactobacillus (preservation number is CGMCC 1.16089), lactobacillus acidophilus (preservation number is CGMCC 1.12735), saccharomyces cerevisiae (preservation number is CGMCC 2.3973), Candida utilis (preservation number is CGMCC 2.3047), Rhizopus oryzae (preservation number is CGMCC3.17463) purchased from China General Microorganisms Culture Management Collection Center to compare as fermentation agent, and specific experimental design is as follows:

[0106] 1) Take 5 g of sterilized mung beans, inoculate 7.5 mL / 100 g of Lactobacillus plantarum, control the fermentation temperature to 26.5 ° C, and ferment for 11 days;

[0107] 2) Take 5 g of sterilized mung beans, inoculate 7.5 mL / 100 g of Lactobacillus acidophilus, control the fermentation temperature to 26.5 ° C, and ferment for 11 days;

[0108] 3) Take 5 g of sterilized mung beans, inoculate 7.5 mL / 100 g of Saccharomyces cerevisiae, control the fermentation temperature at 26.5 ° C, and ferment for 11 days;

[0109] 4) Take 5 g of sterilized mung beans, inoculate 7.5 mL / 100 g of Candida utilis, control the fermentation temperature to 26.5 ° C, and ferment for 11 days;

[0110] 5) Take 5 g of sterilized mung beans, inoculate Aspergillus niger (preservation number CGMCC 3.3928) 7.5 mL / 100 g, control the fermentation temperature to 26.5 ° C, and ferment for 11 days;

[0111] 6) Take 5 g of sterilized mung beans, inoculate 7.5 mL / 100 g of Rhizopus oryzae, control the fermentation temperature to 26.5 ° C, and ferment for 11 days;

[0112] Each group of experiments was repeated three times in parallel; the mung bean pretreatment method was the same as above, and the concentrations of Lactobacillus plantarum, Lactobacillus acidophilus, Saccharomyces cerevisiae, Candida utilis, and Rhizopus oryzae were 1×10 8 After fermentation, the mung beans of each group were dried, crushed, and passed through a 60-mesh sieve, and the polyphenol content and DPPH clearance rate were detected according to the above method. The results are shown in Table 5.

[0113] Table 5 Polyphenol content and DPPH removal rate of mung beans fermented by different fermentation agents

[0114] Experimental Group Polyphenol content (mg / g) DPPH clearance rate (%) Lactobacillus plantarum 8.94±0.26 69.89±1.16 Lactobacillus acidophilus 8.31±0.14 67.14±1.39 Saccharomyces cerevisiae 11.09±0.43 75.89±3.06 Candida utilis 12.86±0.18 83.15±3.34 Aspergillus niger 17.04±0.21 95.07±2.16 Rhizopus oryzae 15.62±0.377 84.47±2.08

[0115] As can be seen from Table 5, using the Aspergillus niger in Example 1 as the fermentation agent, the polyphenol content (17.24±0.21 mg / g) and DPPH clearance rate (95.07±4.16%) in the solid-state fermentation mung bean are significantly higher than those of Lactobacillus plantarum, Lactobacillus acidophilus, Saccharomyces cerevisiae, Candida utilis, Candida utilis, and Rhizopus oryzae, and are close to the predicted values ​​of the response surface experiment in Example 1, indicating that Aspergillus niger is more suitable for the solid-state fermentation of mung bean whole seeds, which is beneficial to the improvement of the polyphenol content and antioxidant capacity in mung beans, and at the same time proves the accuracy and reliability of the process conditions for the solid-state fermentation of mung bean whole seeds.

[0116] Compared with molds, lactic acid bacteria can use starch and protein in mung beans to produce a large amount of acidic substances during the fermentation process, which affects the taste of mung bean products; yeast can use substrate sugars to produce metabolites such as CO2, water and alcohol during the fermentation process. Alcoholic substances are not suitable for consumption by certain groups of people, which limits the development and utilization of mung beans in food. Molds have stronger reproductive ability and stronger enzyme production ability during the fermentation process, which is more conducive to the release of polyphenolic compounds.

[0117] Example 3 Sterilization method comparison experiment

[0118] In order to further verify the enthusiasm and reliability of the sterilization method in raw material pretreatment, the steaming UV sterilization method and the traditional high-pressure sterilization method were used to pretreat mung beans, respectively, to compare the effects of different sterilization methods on the polyphenol content and antioxidant capacity of mung beans, and to verify the sterilization effect of the treatment method. The specific experimental design is as follows:

[0119] (1) Traditional autoclave sterilization: cleaning → soaking → screening → autoclave sterilization at 121℃ for 15min;

[0120] (2) Steaming and UV sterilization: cleaning → soaking → screening → steaming for 10 min → UV sterilization for 30 min;

[0121] The cleaning, soaking and screening were the same as the pretreatment methods in Example 1, and each group repeated 3 parallel tests. After the pretreatment, the mung beans were dried, crushed and sieved through a 60-mesh sieve. The polyphenol content and DPPH clearance rate were detected according to the above method, and the results are shown in Table 6; the mung beans after different pretreatments were bottled and placed at a constant temperature and humidity for 48 hours to observe whether there were colonies and odors in the mung beans, and the results are shown in Table 7.

[0122] Table 6 Effects of different sterilization methods on mung bean polyphenol content and DPPH removal rate

[0123] Experimental Group Polyphenol content (mg / g) DPPH clearance rate (%) Traditional autoclave 4.14±0.31 31.15±2.11 Steaming UV sterilization 6.83±0.17 56.13±1.63

[0124] Table 7 Effect of different sterilization methods on the sterilization effect of mung beans

[0125] Experimental Group Colony Odor Traditional autoclave No colony growth No odor or special smell Steaming UV sterilization No colony growth No odor or special smell

[0126] As shown in Table 6, the polyphenol content and DPPH removal rate of mung beans after boiling UV sterilization were significantly higher than those after traditional high-pressure sterilization.

[0127] As shown in Table 7, both traditional autoclave sterilization and boiling UV sterilization have good sterilization effects, and no colony growth and special odor were observed after 48 hours of storage. However, the temperature of autoclave sterilization can promote the oxidation and hydrolysis of polyphenols, resulting in changes in the structure of polyphenols and loss of effective ingredients. The boiling UV sterilization adopted by the present invention can not only achieve the purpose of sterilization, but also retain the nutritional value of mung beans to a greater extent.

[0128] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for increasing the polyphenol content in mung beans, characterized in that: The following steps are involved: The mung beans are sequentially soaked, steamed in a water bath and sterilized by ultraviolet light to obtain sterilized mung beans; The sterilized mung beans and Aspergillus niger seed liquid are mixed and solid-state fermented to obtain a fermentation product; The mass volume ratio of the sterilized mung bean and the Aspergillus niger seed liquid is 100 g:7-9 mL; the number of viable bacteria in the Aspergillus niger seed liquid is 1×10 8 CFU / mL; the temperature of the solid-state fermentation is 25-27°C; the time of the solid-state fermentation is 10-12 days.

2. The method according to claim 1, characterized in that The Aspergillus niger includes Aspergillus niger that can secrete endo-glucurase, exo-glucurase and glucosidase.

3. The method according to claim 1 or 2, characterized in that: The deposit number of the Aspergillus niger is CGMCC3.3928.

4. The method according to claim 1, characterized in that: The mass volume ratio of the sterilized mung bean and Aspergillus niger seed liquid is 100g:7-8mL; the temperature of the solid-state fermentation is 26-27°C; and the time of the solid-state fermentation is 10.5-11.5d.

5. The method according to claim 1 or 4, characterized in that: The mass volume ratio of the sterilized mung bean and Aspergillus niger seed liquid is 100 g:7.5 mL; the temperature of the solid-state fermentation is 26.5° C.; and the time of the solid-state fermentation is 11 days.

6. The method according to claim 1, characterized in that The water bath cooking time is 5 to 20 minutes.

7. The method according to claim 1, characterized in that The ultraviolet sterilization time is 20 to 40 minutes.

8. The method according to claim 1 or 7, characterized in that: The thickness of the mung beans after water bath cooking during ultraviolet sterilization is 1 to 2 cm.

9. The method according to claim 1, characterized in that: The environmental humidity of the solid-state fermentation is 80% to 100%.

10. The method according to claim 1, characterized in that The mung beans have no white core after soaking.

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