Study On The Correlation Between Microbial Diversity And Nutrient Composition Of Fermented Bean Dregs

Soybean dregs are a by-product of soy milk,tofu or soy processing products.In China,tens of thousands of tons of bean dregs are discarded each year.The high moisture content and cellulose content in fresh bean dregs lead easily to spoilage and rough taste,respectively.Meanwhile,soybean dregs have strong beany flavor and anti-nutritional factors.Therefore,the use of soybean dregs on the foodstuff industry was limited and most of them were dumped as rubbish directly,which results in a great waste of soybean dregs resources and environmental pollution.However,the nutritional value in soybean dregs is similar with that in soybeans,suggesting soybean dregs can be used as a potential health food.In order to improve the comprehensive utilization of soybean dregs and develop a new soybean dregs product,the microorganisms in tranditional fermented soybean dregs were isloated and identified by PCR amplication and High throughout sequencing in this paper,and then some of isolated microorganisms were applied into the fermentaion of fresh soybean dregs,which would improve their taste,flavor and nutritional value.The obtained results are as follows:(1)The mircoorganism of the traditional nature fermented soybean dregs were isolated by different culture media,and identified by PCR amplification and fragment sequencing.A total of 26 strains were isolated and purified,including 5 strains of lactic acid bacteria(Lactobacillus pentosus,Pediococcus lolii,Lactobacillus brevis,Lactobacillus fermentum,Weissella confusa),2 strains of Bacillus(Bacillus subtilis,Bacillus velezensis),2 strains of yeasts(Pichia kudriavzevii,Geotrichum candidu),and 2 strains of fungi(Lichtheimia corymbifera,Lichtheimia ramosa).(2)Metagenomics analysis of microbial communities associated with the traditional nature fermented soybean dregs.The bacterial community in the traditional nature fermented soybean dregs was mainly composed of Proteobacteria and Firmicutes,accounting for63.25%and 36.56%of the sequences on average in each library,respectively.The fungal community was mainly composed of Ascomycota,Basidiomycota and Zygomycota,which accounted for 70.27%,20.88%and 8.85%,respectively.At the genus level,the bacterial community is dominated by Cronobacter(31.71%),Acinetobacter(31.71%)and Staphylococcus(24.26%),and the fungal community is dominated by Rhizopus and Trichosporon,which accouted for 70.26%and 20.87%,on average.(3)Geotrichum candidum,Lichtheimia ramosa and Lichtheimia corymbifera were used as the starting strains in a ratio of 1:1:1,and the inoculation amount was 1×10~7cfu/g,fermented soybean dregs,the effects of fermentation temperature,fermentation time and water content of soybean dregs on total phenolic,total sugar and reducing sugar content,as well as DPPH and ABTS clearance rate were determined by single factor experiment.Response value,through the response surface test analysis,the optimal formula was:fermentation temperature 32°C,fermentation time 6.5 d,soybean residue moisture content was 87.5%,under this fermentation condition,the total phenol content of soybean residue was 105.24 mg GAE/10g.(4)The isolated strains of lactic acid bacteria(Lactobacillus pentosus or Pediococcus lolii,Lactobacillus brevis,Lactobacillus fermentum),Bacillus subtilis,Geotrichum candidum,Lichtheimia ramosa and Lichtheimia corymbifera were used as the starting strain in a ratio of 1:1:1:1:1,it was found that the effect of different lactic acid bacteria on the total phenolic content of bean dregs was not significant(P>0.05),but the effect on DPPH and ABTS clearance rate was significant(P<0.05).(5)Using Caenorhabditis.elegans as a model organism to study the effects of 0 mg/m L,1 mg/m L,5 mg/m L,and 10 mg/m L fermented bean dregs on the lifespan of C.elegans.The results showed that the effect of different concentrations of fermented bean dregs on the lifespan of C.elegans was not significant.The effects of 0 mg/m L and 10 mg/m L fermented soybean residue on the intestinal bacterial community of C.elegans were studied by high-throughput sequencing.The results showed that C.elegans intestine between fermented bean dregs group and control group in the compositional diversity of the bacterial community is high similarity.