Effect of Bacillus subtilis TLO3 Amylase Pre-treatment on Ethanol Production from Raw Starches

Abstract

Bioethanol is currently the most widely used liquid biofuel in the world. Starch rich crops occupy the first place as biomass for bioethanol production. Amylases (EC 3.2.1.1) are enzymes that hydrolyses starch into sugar units, and pre-treating starch with amylolytic bacteria or directly by amylase might have a positive effect on fermentable sugars concentrations and ultimately result in  increased ethanol yields.  In this study, an amylase producer strain Bacillus subtilis TLO3 newly isolated from rhizospheric soil was used for amylase production; after investigating the best combination of physico-chemical parameters. The crude enzyme was used for the pre-treatment of raw corn and wheat starches. Immediately afterwards, the yeast Saccharomyces cerevisiae was inoculated into the saccharified starch solutions for fermentation. Measures were done for total reducing sugars and ethanol production all along the fermentation process. Thus, the best amylase production was obtained using 0.5% starch; 0.5% xylose; 0.25% urea; 2.5% NaCl; 3% bacterial inoculum; pH 7; Temperature 50°C and 24h incubation time. Amounts of reducing sugars of 70% and 91% were obtained after saccharification of wheat and corn starch, respectively, by crude amylase. The fermentation process monitoring showed a continuous decrease in the total sugars, concurrently with an increase in ethanol production that reached 0.92 g/l (2%) for wheat flour and 1.1 g/l (2.4%) for corn flour after 24 h.