Fed-batch production of baker's yeast (S. cerevisiae) from cassava (Manihot esculenta) starch hydrolysate

Abstract

Yeasts are microorganisms in which the unicellular form is conspicuous and outstanding. In this group are the versatile strains of Saccharomyces cerevisiae (Baker's yeast). The local production of Baker's yeast becomes
necessary in Nigeria to replace imported ones being used currently in the industries. The utilization of cassava as a feedstock for the production of baker's yeast using fed-batch fermentation process was investigated. Starch was extracted from freshly harvested cassava tubers and hydrolyzed into fermentable sugar using the enzyme-enzyme method. From the initial starch slurries of 8.84% and 12.40% concentrations, Sugar concentrations of 8.57% and 12.0% respectively were attained. These hydrolysates were used as substrates for the aerobic cultivation of S. cerevisiae under fed-batch conditions for 24 hours with a constant feed rate of 1.1174 L/h. The result obtained revealed that biomass, reducing sugar as well as ethanol concentration increased with fermentation time. The highest ethanol and biomass obtained were 0.060 g ethanol/g glucose and 0.508 g biomass/g glucose. It is noteworthy that the maintenance coefficients of 0.0585 h^-1 and 0.0598 h^-1 for the two runs respectively are low, which is an indication of non stressful metabolism by the micro organism.

Keywords: Baker's yeast, hydrolysis, biomass yield, ethanol yield and maintenance coefficient.