Impact of different nitrogen sources, initial pH and varying inoculum size on the fermentation potential of Saccharomyces cerevisiae on wort obtained from sorghum substrate

Abstract

The influence of different nitrogen sources, initial pH, and varied inoculum size on the fermentation capacity of Saccharomyces cerevisiae on sorghum wort substrate was investigated. The parameters analyzed included ethanol concentration, pH, specific gravity, and total soluble sugars after 72 h fermentation period using standard methods such as specific gravity (bottle) method, refractometer method, and pH meter. Four different nitrogen sources which included urea, diammonium phosphate, ammonium sulfate, and ammonium nitrate, were tested individually using two different concentrations of 0.025% w/v, and 0.05% w/v, to study their influence on the fermentation capacity of the yeast strain. The pH and sugars decreased while the alcohol concentration and acidity increased during the fermentation period (p < 0.05). Ammonium sulfate resulted in the highest alcohol and acidity yield (4.47% ± 0.02%, and 3.65% ± 0.03% respectively) at 0.5% w/v after 72 h fermentation period. The yeast strain performed best at an initial pH of 5.5 and gave an optimum alcohol and acidity yield (4.43% ± 0.01%, and 3.88% ± 0.01% respectively) while inoculum size of 1.24 × 108 cells/ml produced the highest alcohol and acidity yield (4.60% ± 0.01%, and 4.18% ± 0.01% respectively) after 72 h. Saccharomyces cerevisiae is a promising candidate for the fermentation of sorghum wort under optimized conditions of nitrogen, initial pH, and yeast cell number.

Keywords

• nitrogen
• ph
• inoculum sizes
• alcohol
• fermentation
• sorghum wort.