Isolation Of RSGA-Producing Strains And The Enzyme Producing Conditions

Three strains which exhibited strong raw starch-digesting glucoamylase(GARS) activities were isolated from Daqu and soil. They were identified as Aspergillus niger A-6,Paecilomyces sp. P-3,Mucor sp. M-16. Their GARS activities in solid state fermentation were 2461U/g, 2237U/g and 1891U/g respectively; and the RDA values were 21.47%, 15.25%and 27.07% respectively. Their GARS activities in liquid fermentation were 353U/ml, 131U/ml and 115U/ml respectively; and the RDA values were 20.30%, 20.47% and 56.37% respectively. Then the enzyme characters of the crude extracts produced by Aspergillus niger A-6 and Paecilomyces sp. P-3 were studied. The hydrolysis rates of the raw corn flour hydrolyzed by the crude extracts after 24 hours was 88.57% and 86.88% respectively; the optimum pHs for the enzyme activity were 4.0, and the optimum temperatures were 70℃; the enzymes were more stable at the temperature of 60℃ than at the optimum temperature of 70℃, as they lost activities more than 85% after 2 hours at 70℃; it was also found that the α-amylase could improve the enzyme activity slightly towards the raw corn flour. The growth conditions and the solid state fermentation conditions of Paecilomyces sp. P-3 were studied. For the growth of Paecilomyces sp. P-3, the optimum temperature was 30℃ and the optimum initial pH was 5. For the enzyme production in the solid state fermentation, the optimum initial pH was 7, the optimum temperature was 25℃, and the optimum initial moisture content was 80%. Under these optimum conditions, the RSGA activity was 2473U/g after fermented 6 days. The effects of various nitrogen sources, carbon sources and pH on the synthesis of RSGA by Aspergillus niger A-6 were studied. It was found that the pH value was an important factor on the synthesis of RSGA, the synthesis of RSGA was depressed at low pH; and NaNO3 was better than peptone using as nitrogen source in the production of RSGA, as the RDA value was higher. It was also found that corn flour and maltose were more highly inducing carbon sources than other carbohydrates in the production of RSGA. The liquid culture medium optimized by orthogonal experiments was: corn flour 4%, soybean powder 3%, wheat bran 1%, K2HPO4 0.1%, MgSO4·7H2O 0.05%, KCl 0.05%, FeSO4·5H2O 0.001%, Tween80 0.2%, CaCO3 0.15%, and the RSGA activity was 422.5U/mL.