Kinetics of enhanced ethanol productivity using raw starch hydrolyzing glucoamylase from Aspergillus niger mutant produced in solid state fermentation.

AIMS: The present investigation deals with the effect of raw starch hydrolyzing glucoamylase by a derepressed mutant of Aspergillus niger on enhanced productivity of ethanol from uncooked starch under non-aseptic conditions. METHODS AND
RESULTS: The parental culture of Aspergillus niger was improved using gamma-ray treatment. One derepressed mutant was isolated after extensive screening and optimization and grown on corn cobs, maize starch, soluble starch and wheat bran solid media moistened with Vogel's salts solution and corn steep liquor. The mutant was 2.5-fold improved over its parent with respect to enzyme productivity, product yield and specific activity. The enzyme from mutated culture was also improved for enzyme properties and could effectively hydrolyze raw starch without the aid of alpha-amylase. Starch hydrolyzed with mutant-derived glucoamylase supported higher volumetric and product yields of ethanol than those of parental and other strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the present study are of commercial value. Ethanol product yield coefficient, and volumetric productivity revealed the hyper-productivity of ethanol from raw starch hydrolyzate obtained with mutant-derived glucoamylase without addition of liquefying alpha-amylase under non-aseptic conditions.