Enzymatic Production of Ethanol from Cassava Starch Using Two Strains of Saccharomyces cerevisiae

Abstract

Cassava starch from TMS 30572 and Idileru were hydrolyzed with ƒ¿-amylase and amylo-glucosidase before fermentation using two strains of Saccharomyces cerevisiae from palm wine and bakersf yeast. The per cent yield of sugars and total dissolved solids were 66 % and 26% respectively while pH was 7. Spectrophotometric measurement of the cell growth revealed steady but insignificant (p . 0.05) increase in cell concentrations up to 48 h fermentation time with a gradual decline by 72 h. Saccharomyces cerevisiae strain from palm wine grew best on TMS 30572 hydrolysate at 20% sugar concentration (optical density 0.663; fermentation time 48 h) while on Idileru hydrolysate it grew best at 25% (optical density 0.698; fermentation time 60 h). The pH values obtained from the fermenting hydrolysates for both yeast strains declined gradually as the fermentation progressed with the lowest pH values (3.01 for S. cerevisiae from palm wine; 3.06 for S. cerevisiae from bakersf yeast) obtained for TMS 30572 cassava variety at 25% sugar concentration. Changes in pH were significant (p . 0.05). The Saccharomyces cerevisiae strain from palm-wine had a higher conversion of available sugar into ethanol. The yield of ethanol was found to vary but the highest ethanol concentration obtained was 5.3% at 10% initial sugar concentration, which gave a sugar conversion efficiency of 37.3%. The results obtained suggest
that Saccharomyces cerevisiae strains from sources other than those used conventionally can serve as good substitutes for bio-conversion processes in the industrial production of ethanol.

Keywords: Cassava, enzyme, ethanol, Saccharomyces cerevisiae, starch