Bioconversion of soybean residue for use as alternative nutrient source for ethanol fermentation

Soybean residue (SR) was transformed, through solid-state fermentation by Aspergillus oryzae TISTR 3087 followed by hydrolysis, to a solution rich in free amino nitrogen (FAN), and used as the nitrogen source in an ethanol fermentation. Supplementing SR with waste cooked rice (CR) at a 75:25 mass ratio increased dramatically the production of protease compared to a fermentation with SR as the sole substrate (2822 U g(-1) substrate against 33 U g(-1)). Subsequent hydrolysis of the solid-state fermented solids produced as much as 1.8 g-FAN L-1. The SR-derived hydrolysate was mixed with sugarcane molasses, to an initial sugar concentration of 110 g L-1, and used for ethanol production by Saccharomyces cerevisiae TISTR 5339. The yeast produced 40.7 g ethanol L-1 with a yield of 0.42 gg-sugar(-1) and a productivity of 0.62 g L-1 h(-1). This study demonstrates clearly that co-fermentation of SR and CR enhances protease production, and that SR is a feasible and low cost source of nitrogen for ethanol fermentation. (C) 2017 Elsevier B.V. All rights reserved.