Bioconversion of rice straw to sugar using multizyme complex of fungal origin and subsequent production of bioethanol by mixed fermentation of Saccharomyces cerevisiae MTCC 173 and Zymomonas mobilis MTCC 2428

The multidimensional approach for ethanol production from rice straw was opted by three distinct phases: firstly, statistical optimization of β-glucosidase production from co-culture of Aspergillus fumigatus ABK9 and Trichoderma reesei SAP3 through mixed substrate (wheat bran and rice straw) fermentation; secondly, enzymatic saccharification of pretreated rice straw for high yield of reducing sugar and finally, statistical optimization of bioconversion of the sugar to ethanol by mixed fermentation of Saccharomyces cerevisiae MTCC 173 and Zymomonas mobilis MTCC 2428. In optimized media, maximum β-glucosidase yield of 265.4 U g−1 was achieved. Enzymatic treatment (40 U g−1) of NaOH pretreated rice straw produced maximum reducing sugar of 24.9 g L−1. It also showed maximum enzyme adsorption (Emax) by 2 fold and decreased the absorption coefficient (Kad) by 37.64% relative to untreated straw. During ethanol fermentation, inoculum ratio became most influencing factor to maximize ethanol production of 40.1 g L−1, indicating the influencing effect of the perpetrator strains.

► Statistical optimization of mixed fungal mixed substrate solid state fermentation for high yielding of β-glucosidase.
► Improved enzymatic saccharification of pretreated rice straw with high yield of sugars (24.9 g L−1).
► Statistical optimization of ethanol production by S. cerevisiae and Z. mobilis produced significant amount of ethanol (40.1 g L−1).