Abstract

The fermentation process of sugar feedstock materials at industrial scale requires the utilization of microorganisms capable of working at high ethanol concentration and high temperatures. The selection of Saccharomyces cerevisiae strains, able to ferment sugars obtained from different material at temperatures above 35°C with high ethanol yield, has become a necessity. Three yeast strains were irradiated with gamma ray and screened for their ability to grow and ferment molasses in a temperature range of 35-45°C. The yeasts were placed in a liquid medium, and irradiated at different doses (0.1, 1, 2, 3, 4, 5 and 10 KGy/h). Although all the isolated strains had growth (in agar plates) at 35 and 40°C, but just two strains showed growth at 42°C, and there was no growth at 45°C. Two pure yeast strains were isolated (PTCC⁵²⁶⁹ M₃ and Areni M₇). The efficiency of temperature and high concentrations of ethanol tolerant strains were more than double of ethanol production compared with using the initial strains of yeast. All resistant strains were tested on liquid medium of molasses, and nutrients with 30% (v/v) ethanol had significant difference (P>0.01) for growth intensity at same condition with initial strains.

Key words: Bioethanol, gamma radiation, Saccharomyces cerevisiae, thermotolerant.