Abstract

The aim of this work was to research a bioprocess for bioethanol production at laboratory scale from raw sweet potato using Saccharomyces cerevisiae MTCC-170. In order to obtain maximum conversion of starch into fermentable sugar, optimum parameters for the liquefaction were determined as 104 to 105°C, 0.15% v/w of α-amylase enzyme solution (300 U/ml) and 30 g dry-weight sweet potato mash/100 ml distilled water, respectively with a 74.38% loss in dry weight during the process. For saccharification process, the optimum dose of amyloglucosidase was 0.25% v/w (300 U/ml) with 16.82% glucose production at pH 5.0 and temperature 60°C after 1 h. The fermentation parameters like inoculum size, temperature, pH and different concentrations of nutrients were also determined. The maximum ethanol concentration, that is, 7.95% (v/v) was obtained with 10% inoculum size at pH 6.0 after 48 h. Furthermore, out of the three nitrogen sources (yeast extract, peptone and ammonium sulphate) tested for ethanol production, peptone at a concentration of 1.5 g/L was found to be best (7.93%). From the present study, it may be concluded that sweet potato can be an attractive feedstock for bioethanol production from both the economic stand points and environment friendly.

Key words:  Sweet potato starch, ethanol, liquefaction, saccharification, Saccharomyces cerevisiae MTCC-170.