Abstract:

A new strain SP7 with strong gelatinized starch-digesting glucoamylase (RSGA) activity and a synergistic effect on compound enzyme system was isolated from rotten sweet potatoes, which was preliminarily identified as Aspergillus niger by morphologic taxonomy test. A mutant stain, SP7-2 was obtained from SP7 subjected to combined UV and LiCl mutagenesis, which resulted in 3446 U/g RSGA activity under solid-state fermentation and 12.5% (V/V) alcohol degree of liquor brewing with uncooked materials. A broad activity towards raw starch with both small and large granule sizes was observed and glucose was the only hydrolysis product. Substrate specificity of this enzyme exhibited an order from high to low as corn starch, sweet potato starch, potato starch, rice starch, cassava starch and wheat starch. The optimal temperature and pH for enzyme activity towards raw sweet potato starch as a substrate were 40 ℃ and 4.0, respectively. After incubation at 60 ℃ for 1 h, the activity of this enzyme remained less 5%. However, more than 90% of maximum activity was remained after incubation at pH 3.5 for 1 h at room temperature. Therefore, SP7-2 SGA was a temperature-sensitive and acid-tolerant enzyme, which exhibited great prospect in the application of liquor brewing.

Key words: gelatinized starch-digesting glucoamylase, A. niger, breeding, liquor brewing with uncooked materials