Production of ethanol by yeasts grown on hydrolysate of Egyptian sweet potato

ABSTRACT

The influence of different concentrations of HCl for acid hydrolysis of Egyptian sweet potato for maximal ethanol yield was studied. The optimum HCl concentration was 0.5 N with respect to reducing sugars formed [60% DE] and minimum hydroxymethyl furfural content [0.05%] at 97C for 20 minutes. Total solids for Egyptian sweet potato was 27%, reducing sugars and glucose content based on fresh weight were 27.53%, 26.7%, respectively. Both hydrolyzed sweet potato slurry [SPS] and glucose [at concentration 4.5%] were subjected to fermentation by 4 different yeast strains for 4 days of growth. The results showed optimum ethanol yield after 72 hours of fermentation with respect to Saccharomyces cerevisiae, Saccharomyces uvarum yielding 0.3 g/g, 0.31 g/g, respectively. Upon using Pachysolen tannophilus, the maximum ethanol yield was obtained after the first 24 hours 0.24% g/g and Pichia pinus was 0.27 g/g after 48% hours of fermentation. The yields of yeast cells were estimated after 96 hours of fermentation and indicated the presence of high dry weight of cells [4.0-8.5 g/L] with considerable amounts of crude protein [35-45%] and true protein [20.3-27.4%]