Screening of Thermotolent Yeast Isolates for Ethanol Tolerance at Different Temperatures

An ideal microorganism used for ethanol production must have rapid fermentative potential, improved flocculating ability, appreciable sugar tolerance, enhanced ethanol tolerance and good thermotolerance.The ethanol production potential of thermotolerant yeast strains isolated from different fruit waste was investigated.A total of 110 yeasts were isolated from different fruit wastes and were screened to determine thermotolerance by growing at different temperatures viz.35, 40 and 45 o C by using Yeast extract dextrose peptone broth.Among these, 20 yeast isolates grew satisfactorily at all three temperatures viz.35, 40 and 45 o C. Further all the 20 thermotolerant isolates were screened for ethanol tolerance at all three temperatures viz.35, 40 and 45 o C. The broth medium was supplemented with different ethanol concentrations ranging from 5% to 20% (v/v) at temperature (35°C, 40 °C and 45 °C), time (24 h, 48 h, 72 h and 96 h) and growth was measured by OD at 600 nm.Among 20 isolates, four (YP11, YM17, YPA48 and YPA64) were found to be highly tolerant to ethanol 20.0 per cent (v/v) at 35 o C.