Isolation of ethanol-producing yearst from sugarcane plants

Abstract

Sugarcane juice is known to have an abundant nutritional composition, including a fairly rich content of electrolytes, vitamins, minerals and remarkably high percentage of sugars. Even though Vietnam is one of the big sugarcane growers in Asia, there is only a limited understanding of yeast species associated with sugarcane plants in Vietnam and alcohol beverages made from sugarcane juice has not received much attention in the country. As, the qualities of fermented beverages have long been reported to depend on the activities of the yeast(s) involved. Thus, the objective of the current research was to isolate yeast strains from sugarcane plants and evaluate their ethanol producing capacities using sugarcane as the sole substrate. Two sugarcane varieties, including purple and green skinned types, were either peeled or unpeeled and crushed for juice extraction that was used right away for the microbial isolation (direct isolation) or the juice was naturally fermented for one week (enriched culture isolation). Five different yeast strains were isolated and based on their morphological characteristics they were putatively identified as Saccharomyces cerevisiae (D), Candida albicans, and Hanseniaspora vineae, Candida tropicalis and Debaryomyces hansenii. S. cerevisiae, C. albicans, and H. vineae were found in green and purple sugarcane, the yeast strain C. tropicalis was found in green sugarcane and D. hansenii was found in purple sugarcane. The ability to utilize sugarcane juice of the isolated yeasts was record: Before fermentation, the sugarcane juice had the total TSS (18.51± 0.03 oBrix), and the reducing sugar (29.41± 0.01 g.L-1) and these were significantly reduced after 7 days of fermentation in all the cultures. This suggested that the yeasts could utilize sugarcane juice well. However, only yeast strains like S. cerevisiae, C. tropicalis, and D. hansenii were able to ferment sugars into ethanol. In addition, H. vineae and C. albicans hardly produce ethanol. The most potential strain for alcohol production was S. cerevisiae, which produced 12.63 ± 1.11c g.L-1. C. tropicalis and D. hansenii also could produce ethanol production that produced 7.41 ± 1.85b g.L-1 and 7.20 ± 1.15b g.L-1. Therefore, S.cerevisiae(D) is most suitable for ethanol production with the highest fermentation efficiency 88.23 ± 7.97c % and ethanol productivity 0.08 ± 0.007c g.L-1.h-1.