Potential use of low quality sweet potato for ethanol production by response surface methodology

Abstract

Potential use of low quality sweet potato (sweet potato weevil) for ethanol production by hydrolysis and fermentation process was determined in this research. Low quality sweet potato (25% w/v) was hydrolyzed pressure at 121C for 30 min. It was found that maximum content of reducing sugar production was 390.99 g/L. Effects of microorganism strains (S. cerevisiae TISTR 5339, Z. mobilis TISTR 405 by 1% sulfuric acid under 15 lb/in2 and co-culture of Z. mobilis TISTR 405 and S. cerevisiae TISTR 5339) at 10%v/v inoculum, pH 5.5 at 30C for 48 h and effects of reducing sugar content (10, 20 and 30 g/L) on efficiency of ethanol production was studied. Results showed that S. cerevisiae TISTR 5339 was superior in terms of ethanol production compared to Z. mobilis TISTR 405 and co-culture of Z. mobilis TISTR 405 and S. cerevisiae TISTR 5339. Furthermore, kinetic value of this strain was 26.00 g/L, 8.1 and 0.72 g/L/h for P, Y p/s and Q, respectively. The highest ethanol content (5%) was produced when S. cerevisiae TISTR 5339 used with 10%v/v inoculum, pH 5.5 at 30ºC for 48 h. Moreover, effects of ammonium sulphate content (0.05-0.15%), pH (4.5-5.5) and inoculum content (5-10%) on reducing sugar and ethanol content was evaluated with response surface methodology (RSM) in Box-Benhken design. Optimum conditions were 0.05% ammonium sulphate, pH 5.5 and 5% inoculum to show both residual reducing sugar 6.64 g/L and 9.06% ethanol production. Therefore, low quality sweet potato had a promising potential as substrate for ethanol production for sustainably renewable energy resource.