CHARACTERIZATION AND STRESS TOLERANCE OF YEASTS ISOLATED FROM PALM WINE

Most traditional food fermentation processes are incomplete, resulting to products that are proneto rapid deterioration. This is due to the involvement of a mix of microbial strains that arespontaneously introduced from the environment. The selection and use of microbial strains thatcan tolerate the prevailing stressors during fermentation process will drive fermentation tocompletion and generate stable food products. Therefore, this study was carried out to characterizeand determine the stress tolerance of yeast strains isolated from palm wine. Yeasts isolated frompalm wine samples were characterized using phenotypic methods. Yeast isolates were assessed fortolerance to different concentrations of ethanol (4 - 16%) and NaCl (5 - 20%). Total yeast countsin the palm wine samples decreased from log 9 to 7 cfu/ml over 72 hours. Fifteen distinct yeastisolates were identified to belong to four different genera. They include: Saccharomyces (40%),Candida (13.33%), Pichia (26.67%) and Kluyveromyces (20%). S. cerevisiae PWB13 showed thegreatest tolerance to ethanol (4 - 16%) while P. ohmeri PWB32 was the most sensitive strain. S.cerevisiae PWB13 had the highest percentage tolerance to NaCl (5 - 20%). Candida sp. PWA11and P. ohmeri PWB32 were more sensitive to the different concentrations of NaCl. The yeaststrains showed diversity in tolerance to stress conditions and some strains showed potentials toensure complete fermentation of food substrates.Keywords: Fermentation, Yeasts, Stress, Palm wine