Study On The Characteristics Of Mixed Bacteria Fermented Soybean Residue And Its Application In Steamed Bread

Soybean residue is a by-product of soybean refining.Due to its shortcomings such as poor taste and difficulty in storage,it has caused serious problems in its handling.As a method that can improve the quality of soybean residue and enhance the reusability of soybean residue,microbial fermentation has received more and more attention in recent years.In this study,a strain of high acid-producing lactic acid bacteria D26 was selected from two soybean product processing plants in Linyi City,Shandong Province,and homemade soybean residue in the laboratory.It was identified as Lactobacillus Plantarum.Subsequently,the high-acid-producing lactic acid bacteria D26 and Kluyveromyces marxianus preserved in the laboratory were used to ferment the soybean residue with single and mixed bacteria.The changes of main nutrients and free amino acids before and after fermentation of soybean residue were studied,and the changes of volatile substances before and after fermentation of soybean residue were studied by gas chromatography-ion mobility spectroscopy(GC-IMS).Finally,the soybean residue is used to make soybean residue and steamed bread,and the influence of soybean residue addition amount on the quality of dough and steamed bread was studied,in order to provide a method for the re-development and utilization of soybean residue.The main findings are as follows:(1)A strain of high acid-producing lactic acid bacteria D26 was selected from soybean residue through primary screening,re-screening,molecular biological identification and other means,and the acid production reached 2.67% after 24 hours of fermentation in the soybean residue substrate.It was identified as Lactobacillus plantarum;(2)Using Lactobacillus plantarum D26 and Kluyveromyces marxianus to carry out mixed fermentation of soybean residue.The total acid and sensory evaluation were used as inspection indicators,the mixed fermentation condition of soybean residue was optimized by single-factor and orthogonal experiments.Results showed that the optimum fermentation conditions are as follows: material-to-liquid ratio 1:3,inoculation amount6%,temperature 31℃,inoculation ratio 1:1,fermentation time 72h;(3)The changes of main nutrients before and after fermentation of soybean residue were studied.Among them,the protein content of single yeast fermentation group(DK),single lactic acid bacteria fermentation group(DR)and mixed bacteria fermentation group(KD26)were changed from control group(WKB)28.9% decreased to 28.1%,28.3%,and 27.8%,the crude fat content increased from 15.7% to 16.8%,15.8%,and16.4%,and the total dietary fiber content decreased from 52.0% to 50.3%,50.5%,and48.7%,the soluble dietary fiber content increased from 4.2% to 5.9%,5.0% and 7.8%,respectively.In addition,after fermented soybean residue,the total amount of free amino acids increased significantly,from 42 mg /10g(WKB)to 90.8 mg/10g(DR),93.9 mg/10g(DK)and 99.9 mg/10g(KD26);(4)GC-IMS was used to determine the volatile substances before and after the fermentation of soybean residue with single and mixed bacteria.A total of 65 volatile substances were separated from 4 soybean residue samples,and 46 volatile substances were qualitatively determined.The results showed that the aldehydes,such as hexanal and valeraldehyde,decreased obviously after fermented soybean residue.The volatile substances in the mixed-bacteria fermentation group and the single-yeast fermentation group are relatively similar,mainly including ethyl acetate,amyl acetate,isoamyl acetate and other ester substances,and the cumulative contribution rate of the main components of the two samples is 98%.The fermentation group of single lactic acid bacteria contained more alcohol ketones,such as 2-heptanone,2-butanone,hexanol,etc;(5)With the increase in the amount of soybean residue added,the water absorption(WA),development time(DT),stability time(ST)and degree of softening(SD)of the soybean residue dough increased,the specific volume,texture properties,whiteness and sensory scores of soybean residue steamed bread all showed a decreasing trend.Among them,the WA,DT,and ST of unfermented soybean residue dough are larger than fermented soybean residue dough,and SD are all smaller than fermented soybean residue dough;the texture characteristics of fermented soybean residue steamed bread are better than those of unfermented soybean residue steamed bread;the whiteness of the steamed bread skin of fermented soybean residue steamed bread is significantly greater than that of unfermented soybean residue bread.In the fermented soybean residue group,the whiteness of the steamed bread core did not change significantly;the cell density(CD)value of the unfermented soybean residue steamed bread was greater than the fermented group,and the area fraction(AF)was lower than the fermented group;except for 15%(dry basis)addition of soybean residue In addition to the amount,the specific volume and sensory scores of fermented soybean residue steamed bread are greater than unfermented soybean residue steamed bread,and 10%(dry basis)is selected as the optimal addition amount.