Analyses of challenges faced during the production of amylolytic enzymes and bio-ethanol using left-over cooked-rice, and rice unfit for human consumption

Abstract

Rice-based enzyme and alcohol production bio-processes using fungi have been explored for years, but they have suffered from the long-pending predicament of presenting their challenges. Currently, major agricultural countries have been resorting to the usage of surplus first-generation biomass sources in bio-refineries. The present lab-scale work proposes, analyzes, and presents the scale-up challenges of such processes while using a novel mixture of left-over cooked rice and market-rejected rice grains. Fractionated rice grains were used as the substrates for enzyme production. Alpha-amylase (365 IU/mL) was produced by employing Aspergillus oryzae 113 ATCC [9102], while glucoamylase (96 IU/mL) was produced by employing Aspergillus niger A1143 NRRL3 [DSM2466] in separate 144-h-long bio-processes. A mixture of left-over cooked rice and rice grains was sequentially saccharified using the produced enzymes, showing a cumulative 51.66% saccharification. Fermentation of the saccharified hydrolysate using Saccharomyces cerevisiae yielded 59.2 g/L bio-ethanol (starch-conversion: 63.3%) with 190-proof purity (95% v/v). The impact of the enzyme/bio-ethanol production on the coefficients of fungal biomass yield (Yx/s, Yx/O2) and maintenance (msx, mO2x), the rates of specific growth (μ) and substrate uptake (SUR) were analyzed individually. A fundamental techno-economic analysis of the entire process has been presented.