Study On Solid-state Fermentation Of Soybean Meal And Its Protein Emulsification Characteristics

Soybean meal is a high-quality and low-cost plant protein resource.It is widely used in the field of food and feed because of its high protein content,rich nutrition,large output and wide source.As a raw material for food or feed,soybean meal also has some typical problems,such as: heavy bean smell,containing a variety of anti-nutritional factors,which significantly affects the edible quality and value of soybean meal.This article uses microbial fermentation to reduce the content of anti-nutritional factors in soybean meal,improve its flavor and increase the bioavailability of soybean meal,and further study the changes in the biological and processing functions of fermented soybean meal protein.The research content and results are as follows:(1)Mucor racemosus was used as the main strain to explore the effect of fermentation on the nutrition and flavor of soybean meal,the effect of Saccharomyces rouxii and soybean meal ultrasonic pretreatment on the quality of M.racemosus fermented soybean meal.The results showed that M.racemosus could significantly increase the neutral protease activity,soluble protein content,sensory quality,total amino acid and free amino acid content of soybean meal,and effectively reduce the activity of trypsin inhibitor.After fermentation at 28 °C for 60 h,protease activity and soluble protein content of each fermented soybean meal reached the maximum value,and compared with unfermented soybean meal,protease activity of soybean meal fermented by M.racemosus was 1032.4 U/g,contents of soluble protein,total and free amino acids increased by 3.16 times,13.64% and 5.65 times respectively,and trypsin inhibitor activity decreased by 84.57%.Both soybean meal ultrasonic pretreatment and S.rouxii were beneficial to improve the quality of the fermented soybean meal.Among them,content of trypsin inhibitor in S4(Co-fermentation by M.racemosus and S.rouxii after ultrasonic pretreatment)decreased from 4375 to 357.9 U/g,decreased by 92%,free amino acids content increased by 6.69 times,and total amino acids content increased by22.92%,which effectively improved nutrition and sensory quality of soybean meal.(2)A strain of N.crassa Y 2019 with relatively high cellulase and protease production was isolated from mildewed corn stover as a strain of fermented soybean meal,contrasting determination of the fermentation of soybean meal physical and chemical indicators such as protein hydrolysis,cellulase and protease activity and other physiological functional activities like antioxidant and immune.The results showed that fermented soybean meal could significantly degrade trypsin inhibitor in soybean meal,with a degradation rate of 90.1%,effectively degrading soybean meal biomacromolecules and their anti-nutritional factors.Compared with unfermented soybean meal,cellulase and protease activities reached 1849.25 U/g and 278.75 U/g,respectively,and antioxidant activity(DPPH,OH,O2-)and immune activity were significantly improved.The secondary metabolites produced by the fermentation of N.crassa Y 2019 enhance the biological activity of soybean meal,such as the improvement of in vitro antioxidant capacity and the positive regulation of the immune system.(3)Changes in the emulsification function of fermented soybean meal protein.Using soybean meal as raw material,N.crassa Y 2019 was fermented for 0 h,24 h,36 h,48 h,60 h,and 72 h.Proteins of each sample were extracted in the same way,and then incubated at p H 7.0,85 ℃ for 30 min,and added Microalgae oil,followed by coarse milk,high pressure homogenization,to prepare fermented soybean meal protein-microalgae oil emulsion,to study the effect of N.crassa Y 2019 fermentation on soybean meal protein emulsification function.SDS-PAGE analysis showed that with the prolongation of the fermentation time,the protein or subunit bands gradually became shallower,and new low molecular weight bands were produced,and new macromolecular bands were obviously produced at 60 h of fermentation.The DPPH free radical scavenging ability and anti-lipid oxidation ability of fermented soybean protein showed a trend of decreasing first,then increasing and then decreasing,and the antioxidant ability was the strongest after 60 h fermentation.In the six groups of emulsions,the macroscopic stability of the emulsion fermented for 60 h is relatively good,the emulsion particle size is relatively small,and the particle size distribution is relatively uniform.Comprehensive analysis shows that fermentation is beneficial to improve the emulsifying ability of soybean protein,and the emulsification stability of the fermented soybean protein emulsion system constructed with 60 hours of fermentation is the best.