Evaluation of sweet potato for fuel bioethanol production: hydrolysis and fermentation

The enzymatic starch hydrolysis and bioethanol production from a variety of sweet potato developed for bioenergy purposes (K 9807.1) on the basis of its high starch yields, was studied. Drying at 55 degrees C and 95 degrees C of sweet potato neither affected the sugar content nor the starch enzymatic hydrolysis efficiency. Simultaneous saccharification and ethanol fermentations for dry matter ratio of sweet potato to water from 1: 8 to 1: 2 (w/v) were studied. Fresh sweet potato and dried at 55 degrees C (flour) were assayed. At ratios of 1: 8, similar results for fresh sweet potato and flour in terms of ethanol concentration (38-45 g/L), fermentation time (16 h) and sugar conversion (similar to 100%) were found. At higher dry matter content, faster full conversion were observed using flour. A higher ratio than that for fresh sweet potato (1: 2.2) did not improve the final ethanol concentration (100 g/L) and yields. High ethanol yields were found for VHG (very high gravity) conditions. The sweet potato used is an attractive raw matter for fuel ethanol, since up to 4800 L ethanol per hectare can be obtained.