Thermotolerant yeasts and application for ethanol production

A total of 70 thermotolerant yeast strains were isolated at 40oC from 145 samples including fruit, leaves, flowers, soils and oil-palm fruits. Six isolates showed maximum growth at 40oC within 18 h. Three isolates (MIY1, MIY48 and MIY57) were selected based on their ability to ferment glucose and sucrose rapidly (24 h) and showed the maximum temperature for growth at 42oC but it was good at 40oC. MIY57 produced 4.6% (v/v) ethanol at 40oC from a medium containing 15% glucose. The optimum cultivation conditions for growth and ethanol production of MIY57 was 5% inoculum into the fermentation medium containing 15% glucose and 1% yeast extract with initial pH of 4.5 on a shaking incubator at 150 rpm at 40oC. MIY57, under these conditions, produced maximum ethanol of 5.0% (v/v) after 48 h incubation while S. cerevisiae TISTR 5048 produced only 3.7% (v/v). Maximum cell dry weight was 7.2 g/L (at 18 h), again much higher than that of S. cerevisiae TISTR 5048 (4.1 g/L). Based on morphological, physiological and molecular studies, this strain (MIY57) was identified as Saccharomyces cerevisiae