Optimization Of Glucoamylase Production Conditions By Aspergillus Niger

Glucoamylase(GAM)is one of the main type of enzymes in starch hydrolysis and has a wide application.In order to improve the GAM yield and reduce production cost,the partial components of liquid medium producing GAM by Aspergillus niger and characterization of the crude GAM produced were investigated.The conclusions were as follows.Ammonium sulfate used as nitrogen source inhibited the GAM production.GAM yield was decreased with the increase of ammonium sulfate concentration(0.85-6.8 g/L).However,sodium nitrate used as nitrogen source promoted GAM production obviously.The GAM yield increased by 15.9%and 20.9%respectively when soybean flour(2.75%or 3%)supplemented with 1%sodium nitrate was used as nitrogen source to replace 3%soybean flour.The GAM activity increased by 4.7%when soybean meal was used as nitrogen source to substituted for soybean flour.Under the experimental conditions,60 g/L glucose as carbon source decreased the GAM yield and made the fermentation period longer.GAM activity with 80 g/L glucose as carbon source was similar to that with 100 g/L glucose,but the glucose utilization rate was higher when 80 g/L glucose was used as carbon source.The DE values of liquefied corn starch would affect GAM production.The liquefied corn starch at lower DE(6,11)prolonged fermentation period and reduced the GAM yield.Liquefied corn starch at DE 17 and 31 enhanced the GAM yield,resulted in about 8%and 3.4%increase in GAM activity than the control,respectively.Soybean oil at lower concentration(5.5g/L)had little influence on the GAM fermentation.Soybean oil at 11 g/L inhibited the GAMproduction,reduced the speed of GAM production and prolonged the fermentation period.Crude GAM liquid displayed the highest enzyme activity at 60 ℃ and pH4.0-5.0 and the high stability within the rage of 20-40 ℃ and pH5.0-10.0.