Taye Negera Iticha
Fifty seven yeasts isolates were isolated from different Honey samples selection for ethanol tolerance on yeast extract peptone dextrose agar medium. The aim of the study was to isolate and screening ethanol tolerant yeast to optimize maximal ethanol production from honey. All the yeast isolates were first tested for carbohydrate fermentation using Durham tube fermentation method in yeast extract peptone dextrose broth. Four isolates which were relatively high fermentative in Durham tube fermentation method were selected for testing of the isolates for ethanol tolerance. Ethanol tolerance was tested using different concentration made from 97% of absolute ethanol in yeast extract peptone dextrose broth and their growth was determined by measuring optical density of the cells in broth using spectrophotometer at 660nm. Two strains of isolates showed measurable growth in medium containing above 15% of ethanol were selected for further study. Strain HJ2 tolerates 16% ethanol and strain HG4 tolerates 16.5% of ethanol. According to the morphological and biochemical characterization, the selected yeast isolates were belonged to the genus saccharomyces. Under the optimum conditions the maximum yield of ethanol (8.32% and 9.13%) was obtained using HJ12 and HG33 yeast isolates respectively and 7.67 % ethanol by the standard baker’s yeast.