Abstract
Thirty-nine Rhizopus isolates and 9 authentic Rhizopus strains were grown on wheat bran solid culture and assayed for their soluble starch digestive glucoamylase (GA) and raw-starch digestive glucoamylase (GARS). Results showed that the Rhizopus strains tested can be classified into 4 groups based on their GA and GARS production and ratio of GARS to GA. Four Rhizopus isolates and 2 authentic Rhizopus strains produced reasonable amount of GA and GARS activities (GA>100 units/ml and GARS>10 units/ml) in the solid culture extracts, having ratios of GARS to GA activity>0.10. The strain with the highest ratio of GARS to GA (F75) was selected for medium optimization. The highest GA- and GARS-producing Rhizopus strain (IFO 4697), Rhizopus F75 and a good glucoamylase-producing Aspergillus niger (K-20) were cultured using the optimum medium and the glucoamylase enzymes produced were further characterized based on saccharification rate on various raw starches and rates of simultaneous saccharification and fermentation in combination with baker's yeast.
