Preparation Of Soybean Enzymatic Hydrolysate And Its Influence On Fermentation Of Bacillus Thuringiensis

For falling down the molecular weight of soybean protein and ameliorating the fermentation circumstance,this work aimed to degradate the soybean by using proteinase, to prepare soybean enzymatic hydrolysates and to investigate their influence on Bt fermentation.The technical parameter hydrolysis of three proteinase(acid proteinase,1398netural proteinase and 2709alkaline proteinase) was ensured through the study of the temperature, pH,the concentration of soybean and enzyme/soybean ratio.The optimal technical parameters are as follows.Acid proteinase:temperature 55℃,pH 2.5-3.0,concentration of soybean is 12g/100mL and the ratio is 375IU/g.1398netural proteinase:temperature 50℃,pH 7.0,concentration of soybean is 12g/100mL and the ratio is 360IU/g. 2709alkaline proteinase:temperature 50℃,pH 9.0-10.0,concentration of soybean is 12g/100mL and the ratio is 900IU/g.Under these conditions,the enzymolysis liquid named DP1 was prepared by using acid and 1398netural proteinase;the enzymolysis liquid named DP2 was prepared by only using 1398netural proteinase;the enzymolysis liquid named DP3 was prepared by using 2709alkaline and netural proteinase.The result of component analysis showed that the hydrolysis degree of DP1,DP2 and DP3 were 38.07%,30.49%and 18.22%,respectively and the concentration and oligopeptide were reduced respectively one by one.On the basis,the soybean enzymatic hydrolysate named D1,D2 and D3,respectively were gained by spray drying.The effect of soybean enzymatic hydrolysate as nitrogen was studied in the liquid fermentation and turbid fermentation,respectively.Peptone in PM medium was replaced by D1,D2 and D3,respectively and its influence on growth of Bt D1-23 was studied.The result was indicated that D1,D2 and D3 could observably enhance bacterial density all and the effect of D3 was the best.But the bacteria count,the yield of ICPs and the inhabited diameter of Zwittermicin A were descend when the soybean in H8 medium was replaced by D3.Based on the H8 medium,as the production of ICPs as the main content,and consideration to bacterial count and Zwittermicin A,the component of medium named H15 was builded and optimized as following(g/L):D3,20.0;peptone,2.5;yeast powder, 20.0;corn steep liquor,25;corn starch,25.0.The bacteria count,the yield of ICPs and the inhabited diameter of Zwittermicin A were 2.56×10~9CFU/mL,1.79mg/mL and 12.9mm, respectively in H15 medium.The effects of initial pH on H15 medium and the effect of D1,D2 and D3 on Bt fermentation were studied.The result showed the fit initial pH was 7.0-7.2;D1 and D2 could improve the yield of ICPs and Zwittermicin A,respectively, and D3 could increase the bacterial breed.The reason of the lower production of ICPs in H15 medium comparing to H8 medium on Bt D1-23 fermentation was studied.The result of adding NaCl in H8 medium was showed that the bacteria beed was damaged.The result of adding discarded substance of DP3 in H15 medium was showed that the yield of ICPs was increased.So, we conjectured the reason of low yield in H15 medium was due to the containing NaCl in the enzymolysis liquid and the losing the available substance in prepared process. The effect of D3 as fed material was studied on fed-batch fermentation of Bt D1-23 in H8 medium.It showed that the adding of D3 could promote Bt reproduce and increased the yield of ICPs and Zwittermicin A,and they improved by the rate of 19.4%, 19.7%and 5.4%,respectively.So,the soybean enzymatic hydrolysate was worth consideredwhen when nitrogen source was choosed as feeding material.