The Mutation Of Aspergillus Niger And Optimization Of The Mutant Strain’s Fermentation Process For Producing High Temperature Resistant Glucoamylase And Studying On Its Characteristics

Glucoamylase, which is called glucosamine sulfohyrolase, is derived from aspergillus species. It is widely used in the brewing, the sugar industry, food processing and fermentation industry. It is one of the most popular enzymes in the world. As the key enzymes, glucoamylase is widely used in the deep processing of corn. However, in the process of starch hydrolysis, the repeated heating and cooling is necessary, which caused the huge waste of energy, loss of production equipment. Therefore, we need to improve the optimum temperature of glucoamylase to reduce the energy consumption in the process.This study is based on the original strain of Aspergillus niger. We use composite processing factor of UV and DES to get a heat-type glucoamylase mutant strain UD9. Then we optimize the liquid fermentation and technology of the strains. Besides, we study the enzymatic properties of glucoamylase to lay a theoretical foundation of production.First of all, we optimize the liquid fermentation of Aspergillus niger UD9, using the response surface methodology, and get the optimal choice of liquid fermentation: corn starch 218g/L, corn steep liquor +soybean cake powder(3:2) 57.7g/L, MgSO4 0.27g/L, K2HPO4 0.5 g/L, KH2PO4 0.5 g/L, FeSO4 0.03 g/L; the optimal choice of fermentation technology: temperature 33.0℃, pH=5.0, initial inoculum dosage 5%, rotate speed 196r/min. Under this experiment conditions, the enzymes activity of glucoamylase is 61.55kU/mL, which is 1.2 times of the previous experience.Then we purified the glucoamylase and explored its properties. Finally we determined the optimum temperature is 67℃, the optimum pH value is 4.5, thermal stability is greatly improved than the original strains. Compared with the original strains, change of the optimal catalytic pH and metal ions stability is unconspicuous, the optimum p H value is 4.5; K+、Mg2+、Ca2+ has promoting effect to the saccharifying enzyme catalytic activity, andAg+、Hg2+、Fe2+、Cu2+、Zn2+、Ba2+ and EDTA have different degrees of inhibitory effect on enzyme activity.