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

PurposeCashew 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 (YP/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.MethodsWith 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.ResultsThe 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 (Pm) 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 YP/S value of 0.34 g/g, ethanol concentration of 51 g/L and the productivity was 0.71 g/L/h.ConclusionThe 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. Feni, a widely acclaimed alcoholic beverage, is produced by the distillation process of fermented cashew fruit juice. The enduring tradition holds a profound presence within the societal structure of the region and possesses significant cultural significance. Various individuals contribute at different stages of the Feni-making process, including family members, neighbours, and employees. In the current era characterised by modernity, it is imperative to have a solid understanding of the scientific principles that form the foundation of manufacturing processes. Therefore, researchers have drawn ideas from yeast-based ethanol production, implementing slight modifications to the beverage manufacturing process while preserving its core conventional techniques. This study seeks to assess the performance of two yeast strain isolates, namely Saccharomyces cerevisiae and Pichia kudriavzevii, in enhancing Feni production. These isolates were derived from fermented cashew apple juice. Tolerance testing were carried out to evaluate the suitability of sugar and ethanol for the purpose of ethanol production.