Optimization Of Fermentation Conditions And Control Of Fermentation Process In Glucoamylase Production By Aspergillus Niger

Glucoamylase was widely used in food,fermentation,textile and medicine industries.It had became the largest variety of enzyme products.In order to improve the glucoamylase yield and reduce the production cost by submerged fermentation of Aspergillus niger,the carbon sources and nitrogen sources of fermentation medium were optimized and the effects of feeding time and feeding mode on glucoamylase fermentation were investigated.In addition,the kinds of extracellular enzyme by Aspergillus niger during fermentation were also studied.The main conclusions were as follows.The strain of Aspergillus niger could produce high active glucoamylase and certainα-amylase and protease,but no cellulase,pectinase and lipase were determined in fermentation broth.Using liquefied starch or liquefied corn flour as carbon source had an obvious effect on glucoamylase fermentation.At the same concentration,the liquefied starch was more favorable than liquefied corn flour to produce glucoamylase.The highest glucoamylase activity was obtained when starch and corn flour were liquefied to DE 20.Compared with the initial fermentation medium(the medium compositions were 30 g/L soybean meal,30 g/L corn steep liquor and 100 g/L glucose),which was used as control group,100 g/L liquefied starch was used as carbon source could increase the glucoamylase activity by 7.7%.When 110 g/L and 140 g/L liquefied corn flour were used as carbon sources,the glucoamylase activity was increased by 2.6%and 10.3%respectively*The indigestible dextrin as carbon source had no effect on glucoamylase fermentation,but could improve the α-amylase activity.Adding nitrate into the initial fermentation medium had a positive effect on glucoamylase fermentation and enhanced the pH value of fermentation broth during the fermentation.The addition of 2 g/L or 3 g/L sodium nitrate into initial fermentation medium could increase the glucoamylase activity by 26%and 16%respectively,compared with the control group.Adding sodium nitrate into the initial medium for only once before fermentation was better than fed-batch fermentation.Adding 2 g/L sodium nitrate into the initial fermentation medium and reducing the concentration of soybean meal to 25 g/L could increase the glucoamylase activity by 15.4%.The addition of 1 g/L ammonium nitrate in initial fermentation medium increased the glucoanylase activity by 7.2%.The feeding time and the times of feeding glucose affected glucoamylase yield.The best feeding time was the forth day of fermentation and the glucoamylase activity was increased by 6%when 35 g/L glucose was fed,compared with batch fermentation.It was better to feed glucose once a batch under the eondition of the total feeding amount of glucose was same,Fed-batch fermentation had no obvious effect on α-amylase activity and protease activity produced by Aspergillus niger.