Bioconversion of brewer’s rice into ethanol by Saccharomyces cerevisiae using commercial amylases

This study proposes a circular economy strategy for turning brewer’s rice, a cheap byproduct of the rice milling sector, into ethanol. The liquefied starch polymer is employed with alpha-amylase and then followed by gluco-amylase to act on, which resulted in 81%–94% hydrolysis by single digestion primarily. In the second approach called double digestion, both the alpha-Amylase and Gluco-Amylase were added in a single step which resulted in 52%–72% hydrolysis. When comparing S1 and S2 enzymes, S1 has led to 20%–22% more saccharification than S2. The glucose thus formed was optimally utilized (95%–98%) by two yeast strains OBC14 and NCIM3640. The percentage of glucose utilization was 96% and 99% for 24 and 36 hours, respectively. The fermentation efficiency of NCIM 3640 (GSR) strain showed an ethanol yield of 89% which resulted in 40.72 g/l with 0.45 g/g when employed with S1 and 96% with S2 which resulted in 34.59 g/l ethanol with 0.4 g/g. The fermentation efficiency of OBC14 strain showed an ethanol yield of 98% efficiency with 30.75 g/l, 0.50 g/g using S1, and 96% which resulted in 25.25 g/l with 0.49 g/g when employed with S2.