Investigating the Potential of Ethanol and Sugar Tolerant Yeast Strain Isolates from Fermented Cashew Apple Juice for Improved Feni Production

Cashew Apple Juice (CAJ), rich in reducing sugars, is used to make a Geographical Indication alcoholic beverage named “Feni,” with a unique aroma. However, the alcohol yield from the reducing sugar (Y_P/S) of CAJ has been assessed to be as low as 0.24 g/g against the theoretical yield of 0.51 g/g. This poor yield of alcohol is mainly attributed to the inadequate monitoring and control of the fermentation process.

With the aim to improve ethanol production from CAJ, the current work involved identifying the potent strains, evaluating their alcohol production potential through sugar and ethanol tolerance studies, and studying the effect of C/N ratio on ethanol production by supplementing readily available urea as the nitrogen source.

The isolates Saccharomyces cerevisiae and Pichia kudriavzevii showed reducing sugar tolerance up to 25% w/v but varied in their ethanol production capabilities. Furthermore, the kinetic models describing the ethanol inhibition on the growth rate and ethanol production revealed that the maximum concentration of ethanol beyond which the cell growth was completely inhibited (P_m) was 80 g/L, and the maximum ethanol production above which cells do not produce ethanol (P’_m) was 96 g/L. P. kudriavzevii showed a 41.6% increase in the ethanol yield with a Y_P/S value of 0.34 g/g, ethanol concentration of 51 g/L and the productivity was 0.71 g/L/h.

The current study suggests that high sugar and ethanol-tolerant P. kudriavzevii could be used as a potent starter culture for producing alcohol and cashew Feni from cashew apple juice.