Genetic Characterization of Osmotolerant Fermentative Saccharomyces Yeasts from Tanzania Suitable for Industrial Very High Gravity Fermentation

Abstract

Naturally occurring yeasts were sought from diverse Tanzanian environments and screened for industrial application. The yeasts were isolated from environments such as traditional brews and wines from various parts of Tanzania. In this regard, a total of thirty yeast isolates were screened for their suitability in Industrial Very High Gravity Fermentation (VHGF). Five of these isolates were able to grow and ferment medium with 40% initial sucrose concentration. Whereby, three were able to grow and ferment medium with 700g/Litre (70% w/w) initial sucrose concentration. One of the three isolates coded LB2 isolated from a traditional Makonde sorghum brew was able to ferment a medium with initial sucrose concentration of 1000g/Litre (100 % w/w) at 30 EsC. On the basis of PCR-RFLP of the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA), all the three most osmotolerant isolates were identified to belong to the Saccharomyces sensu stricto clade. Phylogenetic analysis of the 650bp D1D2 domain of the large subunit 26S rDNA of the isolate LB2 clustered this isolate away from the so far known typical osmotolerant yeasts. The fermentation by LB2 isolate of 100% gravity substrate observed in this work is higher than any other encountered in the literatures reviewed. Key words: Osmotolerant, PCR-RFLP, Saccharomyces, traditional brews, very high gravity fermentation (VHGF).