| Soybean meal(SBM)is a good vegetable protein source to replace fish meal.However antinutritional factors in SBM,especially heat-stable anti-nutritional factors(ANFs)such as glycinin and β-conglycinin,restrict its mass application in aquatic feeds.Fermentation is an efficient method to degrade ANFs and improve the nutritional value of SBM.Furthermore,the mix strains fermentation has advantages over single bacterial fermentation in improving nutritional quality of SBM.Bacillus pumilus SE5,an excellent probiotic,which was isolated from the intestine of grouper Epinephelus coioides,could modulate the intestinal microbiota,improve growth performance and immunity and also reduce feed coefficient in marine fish.The SE5 fermented soybean meal(FSBM)has low ANFs and could relieve damage of fish intestine when used as aquatic feed.In this study,Lactococcus lactis 17 and Saccharomyces cerevisiae Sa with good fermentation potentiality,which were selected from our laboratories and cooperative enterprises,were combined with SE5 for SBM fermentation.At same time,the fermentation conditions of FSBM were optimized and experimental indicators of mix strains and single strain fermented SBM were analyzed in order to optimize the fermentation process for producing high-quality aquatic functional FSBM.The main results are as follows:(1)Screening of candidate strainsThe growth curve results showed that Lactococcus lactis 17 entered the rapid growth period after 12 h of culture and Saccharomyces cerevisiae Sa entered the rapid growth period after 9 h of culture.After 24 h of culture,the lactic acid content in the culture solution of Lactococcus lactis 17 reached 15.28 mmol/L.the FSBM of both strains showed good sensory quality.After fermentation by Lactococcus lactis 17,the degradation rates of glycinin and β-conglycinin were 37.29%and 37.29%,respectively.After fermentation by Saccharomyces cerevisiae Sa,the degradation rates of glycinin and β-conglycinin were 37.06%and 13.60%,respectively.(2)Study on the fermentation process of mix strainsThe proportion of strains,order of strains inoculation,the ratio of materials and water,microbial inoculation quantity,fermentation temperature,fermentation time of mix strains fermented SBM were determined by analysis of antigen protein content in FSBM through single factor experiment.The orthogonal results displayed the optimized conditions of mix strains FSBM for degradation of glycinin and β-conglycinin.The best strains compatibility ratio was 2(Bacillus pumilus SE5):2(Saccharoomyces cerevisiae Sa):1(Lactococcus lactis 17).The best inoculation order is Bacillus pumilus SE5 fermented at first and 12 h later,Saccharomyces cerevisiae Sa was inoculated and another 12 h later Lactococcus lactis 17 was inoculated.The optimized fermentation conditions were fermentation temperature 30℃,total inoculation 10%,the ratio of materials and water 1:1,fermentation time 48 h.The contents of glycinin and β-conglycinin under this process were 41.75 mg/g and 32.23 mg/g,respectively,and the degradation rates were 71.48%and 73.37%,respectively.(3)Analysis of nutritional values of single strain and mix strains fermented soybean meal.The crude protein,acid-soluble protein,total free amino acids and crude protein digestibility of the mix strains FSBM were 56.43%,13.60%,2.44%and 51.35%,respectively,which was better than that of the single strain FSBM.The content of soybean peptides in SE5 FSBM was 11.25%,which is higher than that of other FSBM.The crude fat content of Lactococcus lactis 17 FSBM was 2.06%,which is higher than other FSBM.The total fat and free amino acid content of Saccharomyces cerevisiae Sa fermented FSBM was similar to SBM.The mix strains and single strain fermentation improved the sensory quality of SBM.The mix strains and single strain fermentation could effectively degrade the antigen protein and trypsin inhibitory.The number of viable bacteria in each single strain fermented SBM increased after fermentation,and similar results were proved in the mix strains FSBM.The lactic acid content of dry and wet mix strains fermented SBM reached 2.23%and 6.19%,which was higher than that of Lactococcus lactis 17 FSBM. |
