Technology Research On Solid-State Fermentation And Enzymatic Hydrolysis Of Soybean Meal

Soybean meal is an important plant feed protein source with rich nutrients and extensive sources.Because of the high molecular weight and compact structure,the main nutrient protein in soybean meal is hard to be digested and utilized,which resulting in resource waste and the increase of feed cost.Nowadays,the use of biotechnology in soybean meal is one of the developing trend.Biological methods to improve soybean meal mainly include fermentation and enzymatic hydrolysis.Microbial fermented soybean meal has good palatability and attractiveness,and produces additional "microbial-derived nutrients".Enzyme hydrolyzed soybean meal has good nutritional value with the role of specific sites and high degree of proteolysis.In view of the above background,the fermentation of soybean meal(FSBM),enzymatic hydrolysis of soybean meal and bacteria-enzyme compound fermented soybean meal were studied in this paper.By means of the comprehensive analysis of the clue indexes such as sensory,pH,crude protein content and protein hydrolysis degree,the effects of different treatments on soybean meal were compared and the suitable technological conditions for improving soybean meal were determined.The main results were as follows:First of all,the strains suitable for soybean meal ferementation,such as Bacillus subtilis,Saccharomyces cerevisae,Lactic acid bacteria(combined with Lactobacillus bulgaricus and Streptococcus thermophilus),were chosed to carry out the single factor fermentation tests.By determing the crude protein content as the main evaluation index,the effects of fermentation temperature,ratio of material to water(M/W),inoculation amount and fermentation time on the quality of FSBM were studied.The results showed that the optimal conditions for Bacillus subtilis FSBM preparation were temperature 37°C,M/W 1:1,inoculation amount 5% and fermentation time 48 h,respectively.The optimal conditions for Saccharomyces cerevisae FSBM preparation were 31°C,1:1.5% and 60 h,respectively.The optimal conditions for Lactic acid bacteria FSBM preparation were 37°C,1:1.2.5% and 72 h,respectively.Under the optimal conditions of single bacteria fermentations,the CP content was 62.3%(Bacillus subtilis FSBM),53.8%(Saccharomyces cerevisae FSBM)and 48.6%(Lactic acid bacteria FSBM),respectively.Moreover,the dynamic changes of single bacteria fermentation were analyzed and compared on the basis of the optimized conditions of the three kinds of FSBM.It was found that the FSBM fermented with different strains had their own unique characteristics.Bacillus subtilis FSBM hadthe highest CP content growth rate with the flavor of the sauce and basic pH.The CP content growth rate of Saccharomyces cerevisae FSBM sample was not as large as the former,but the yeast flavor and acidic pH were more suitable for livestock and poultry animal feed.Lactic acid bacteria FSBM had the lowest CP content,but the sample with the acid flavor and low acidity value could improve the palatability and attractability of the diet,and so the quality of soybean meal was also improved.Furthermore,exogenous enzymes(neutral protease,acid protease,cellulase,xylanase)were combinedly added one by one to hydrolyze soybean meal with the single factor test.The effects of enzyme dosage and enzymolysis time on the quality of soybean meal were investigated by using protein hydrolysis as the main evaluation index.It was shown that the neutral protease could achieve the excellent effect after hydrolyzed the soybean meal with 30 U/g enzyme for 48 h.On this basis,with the aid of extra 50 U/g of acid protease,or extra adding 50 U/g acid protease and of cellulase,or extra adding 50 U/g acid protease,cellulase and xylanase,the quality of soybean meal had been greatly improved after combined enzyming one by one for 48 h.Under the optimum conditions of enzymatic hydrolysis,the degree of protein hydrolysis was20.1%(single enzyme),22.7%(double combined enzymes),18.3%(three combined enzymes)and 18.3%(four combined enzymes),respectively.Based on the different enzyme combinations,the digestion process of soybean meal was analyzed under the optimal conditions of the each group.It was found that the role of single enzyme can get a good soybean meal protein hydrolysis.Under the action of double enzyme hydrolysis,complex structure of the saccharide got effectively degraded to more simple carbohydrates,and total sugar content was up to 18%.Reduced sugar release increased by 1% after adding cellulase.With the addition of xylanase in four enzymes combination,each indicator fluctuated little.The hydrolysis effect of the two kinds of NSP enzymes was not obvious,indicating that the optimal hydrolysis effect couldn't achieved in the addition of the neutral and acidic protease.Finally,in order to increase the protein hydrolyzate and reduced sugar content,and reduce the content of total sugar,the appropriate enzymes were added to assist in the further fermentation of FSBM based the optimization of Bacillus subtilis,Saccharomyces cerevisiae and Lactobacillus FSBM to improve the quality of soybean meal.For Bacillus subtilis FSBM,when the ratio of neutral protease to cellulase was 5:1 and the total content of enzymes was 0.035%,the degree of proteolysis was increased by about 2%,and the reducing sugar released 1.8% and the total sugar content was 6.8%.For Saccharomyces cerevisiae FSBM,when the ratio of neutral protease to acid protease was 5:1 and 0.035% total amount of enzymes was added,the degree of protein hydrolysis was significantly increased to 18.2%,but the content of reducing sugar andtotal sugar decreased to 1.2% and 16.5% compared with the no enzyme added group,respectively.For Lactic acid bacteria FSBM,when the ratio of neutral protease to acid protease was 2:1 and the total amount of enzymes was 0.56%,the degree of protein hydrolysis,reducing sugar release and total sugar content was 10.8%,4.1%,7.9%,respectively.The indicators of Lactic acid bacteria FSBM had been further improved compared with the control group.