Study On Solid State Enzymolysis And Fermentation Process Of Soybean Polypeptides

The defatted soybean meal is the most important protein material of feed industry.The protein content of it is about 40%-50%, which is complete protein. Although theprotein is abundant and complete, the application of soybean meal is limited because ofthe existence of anti-nutritional factors, such as macromolecular antigen and trypsininhibitor, which is disadvantage in feedstuff. Those proteins in crude feed may result indisorder of immunologic system, anaphylaxis, diarrhoea and dyspepsia, even death.This work is to screen the strains with a high-yield protease or complex enzymes,which can degrade the soybean protein to the polypeptide. Through those processes, thesoybean antigen is broken and the feeding value of soybean meal is heightened.The study included two phases. Firstly, after strains screening, we have obtained twostrains, named S3 and S2 respectively. Based on acidic protease activity, we puted to themultifactor experiment of the culture medium for S3 strain by response surface analysis.The equation of polynomial regression was established between those factors and theresponse, which was Y₁=—9968.58+47169.7X₁+3406.345X₂+5814.607X₃+5234.83X₄—102395.1X₁X₁—3531.875X₁X₂—871.5759X₂X₂+530.375X₂X₃—3491.804X₃X₃—793.2009X₄X₄. Through this equation, the optimum condition wasobtained and included as follows: ratio of soybean meal to wheat bran 1:0.20, （NH₄）₂SO₄1.9%, NaNO₃ 0.97% and KH₂PO₃ 1.00%. Under the optimum level, the acidic proteaseactivity reached 9000U/g, which increased 120% over pre-optimization. Secondly,according to the hydrolysis degree, on the ground of single factor experiment, weproceeded to the multifactor experiment of solid state enzymolysis and fermentationprocess by response surface analysis. The equation of polynomial regression wasestablished between those factors and the response, which was Y₁=—17.4439+24.73894X₁+1.178839X₂+0.092014X₃+9.132388X₄—13.31702X₁X₁+3.025X₁X₂—0.557314X₂X₂—3.275709X₄X₄. Through this equation, the optimum condition wasobtained and included as follows: ratio of soybean meal to water 1:1.00, enzymeconcentration 2.55%, fermentation time 65h and inoculum concentration 1.00%. Underthe optimum level, the hydrolysis degree reached 13.3%, which increased 56% overpre-optimization.We done the magnification experiment of solid state enzymolysis and fermentationprocess. The results showed that, under the tray, the datum was similar with the mini-test,and under the condition of 200kg soybean meal, the datum was only 11.1%, whichdecreased 16.5% over mini-test.