Soybean waste (okara) as a valorization biomass for the bioethanol production

Okara, an agricultural waste product that is generated in abundance by the soy industry, has tremendous potential for use as renewable biomass rather than being disposed off in landfills or incinerated. We investigated the feasibility of using okara as a raw material for the production of bioethanol using hydrolytic enzymes produced in-house and analyzed its content in fermentable sugars such as glucose and galactose, which can be fermented by Saccharomyces cerevisiae. We also performed a comparative study of the activities of hydrolytic enzymes produced in-house from various fungal species on okara biomass. The in-house enzymes were produced from fungi using okara as a carbon source and tested on okara biomass for their hydrolytic activity. The okara biomass was used raw or pretreated in an autoclave (moist heating) for 20 min at 121 °C. The chemical compositions content of raw and autoclaved biomass exhibited little difference; however, the enzymatic conversion rate increased significantly from 21.9% for the raw okara to 82.9% for the pretreated okara. The ethanol conversion yield (based on sugar content) from enzymatic hydrolysis after S. cerevisiae fermentation was 96.2%.