Saccharification of biopretreated paddy straw with indigenous holocellulase and fermentation with Saccharomyces cerevisiae LN1 under optimized conditions

Abstract

The current study was aimed at optimizing the fermentation conditions for efficient ethanol production from biologically pretreated paddy straw. The yeast strain Saccharomyces cerevisiae LN1 showed highest fermentation efficiency at pH 5.0 and temperature 30 °C. Paddy straw pretreated with fungus Myrothecium roridum LG7 was saccharified with indigenous holocellulase from Aspergillus niger SH3 producing total sugar yield of 26.14 mg/ml with 19.23 mg/ml of glucose. Enzymatic hydrolysate was then fermented using S. cerevisiae LN1 to observe the effect of nutrient supplementation (yeast extract, MgSO4·7H2O and (NH4)2SO4) on ethanol production. Higher ethanol was produced from saccharified material fermented without supplementation of any nutrient source. With the scale-up of ethanol production under optimized conditions in 7L bioreactor, 4.46 g/l of ethanol was produced with fermentation efficiency of 47.2 %. TLC of enzymatic hydrolysate confirmed the presence of p-coumaric acid, ferulic acid, vanillic acid, gallic acid and many other aromatic compounds and inhibitors in the saccharified material which limit fermentation efficiency of yeast strain. Thus, optimization of fermentation conditions can lead to development of a cost-effective process for efficient ethanol production, exploitation of which also requires removal of aromatic compounds and inhibitors which may hinder the ethanol production efficiency.