Ethanol Production by Alcohol Tolerant Yeasts Using Different Carbohydrate Sources

Abstract

This study aimed at comparing the ability of two indigenous yeast species; Pichia kudriavzevii strains GY1 and L9 with a strain of Saccharomyces cerevisiae, to consume sugars (fructose, galactose, glucose, lactose, sucrose and molasses) and to convert them into ethanol during fermentation. Yeast extract (6g/L), peptone (10g/L), malt extract (6g/L) broth was supplemented with different concentrations (5g/L, 10g/L, 20g/L, 30g/L) of fructose, galactose, glucose, lactose and sucrose respectively. Sugar utilization post incubation for 96 hours at 120 rpm, 30 degree Celsius (°C) was measured using a refractometer. The alcoholic yield using molasses for Pichia kudriavzevii strain GY1 10±0.2 (mg/ml) was significantly higher than that of Pichia kudriavzevii strain L9 (4±0.2 mg/ml) and Saccharomyces cerevisiae strain T (5±0.2 mg/ml) at 96 hours. Strains that produced highest concentration ethanol was Pichia kudriavzevii strain L9 in 3.0% (v/v) galactose and fructose respectively, which measured at 7.1±0.48 (mg/ml) and 12.2±0.64 (mg/ml). All studied isolates produced the same amount of ethanol 9.1±0.52 (mg/ml). The use of highly adaptable non Saccharomyces yeast species to a variety of sugars in the pursuit of enhanced ethanol production creates a unique prospective for large scale industrial applications.