Screening Of Soymilk Coagulating Enzyme-producing Strain And Study On Its Optimization Of Fermentation Conditions And Enzymology Properties

Soymilk Coagulating Enzyme is a general term referring to the enzyme which can make protein in soymilk gelation. It is mainly applied to the making of tofu. After many experiment, A strain was isolated from soy-whey. Its product of fermentation has a better function of Soymilk Coagulating., Processing in 100℃, The product of fermentation will lose its Soymilk Coagulating activity which can be regarded the gelation produced by enzyme. The strain is named HS-D11, which by its form is identified as Mucor.Studying on the effects of carbon sources and other influence factors optimized the fermentation condition for the strain. The optimal medium composition for the strain growth is corn flour 2%, soybean power 3%, NaCl 0.05%, MgSO40.02% , K2HPO40.1%,The optimal fermentation conditions for Soymilk Coagulating Enzyme producing are initial pH 5.5~6.0, culture medium volumes for 50 mL in 250mL flask, inoculation for 5%, cultivated at 30℃ with an aeration rate of 150rpm for 48h; Then cultivated at 28 ℃ under untouch for 72h, at last a maximum yield of 1.16 U/mL was obtained.The research on the enzymatic characteristics in the supernatant solution of the culture fluids indicates that the optimal temperature is 65 ℃, the enzyme isunstable in different temperatures. It would lose its activity when it is in 70C for 40 minutes, the optimal pH is 5.9, it is stable in the pH range 5.0~6.0. In addition, the addition of Ca2+ , Mg2+ can best promote the activity of Soymilk Coagulating Enzyme. Meanwhile the research on the effect of the enzyme in soymilk shows that 0.5mL supernatant solution of the culture fluids in 10min under 65C can make 5mL soymilk solid. During the experiment the supernatant of soymilk will become clearer and the percentage of protein recycling in soymilk can reach to 90.3%. Comparison of the effect produced by 10mmolCaCl2, pH4.5 and Soymilk Coagulating Enzyme indicates that the 10mmolCaCl2 in which the proportion between height of supernatant solution and the height of deposition is around 2 : 1 ,while the proportion of effect of Soymilk Coagulating Enzyme is smaller in which the proportion is around 1:1. The effect of CaCl2 and pH doesn't change the secondary structure of the soybean protein so that the granule of the sedimentation is larger and its rate is faster. The effect of enzyme does not only destroy hydrophobic bond and disulfide bond in the higher structure in the protein but also affect some certain kind of peptide bond that the sedimentation rate of the soybean protein reduce.