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.
Highlights
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
Saccharomyces cerevisiae is an important microorganism in bio-industry and its tolerance to temperature and ethanol concentration is one of the main characteristics used for deciding whether it can be used as a bio-fermentation resource (Osho, 2005)
One of the problems associated with fermentation of sugar is the high temperatures (35-45°C) and high ethanol concentration
Summary
Saccharomyces cerevisiae is an important microorganism in bio-industry and its tolerance to temperature and ethanol concentration is one of the main characteristics used for deciding whether it can be used as a bio-fermentation resource (Osho, 2005). Tolerance to high temperatures and ethanol concentrations are important factors of microorganisms for increasing efficiency at industrial scale. The fermentation efficiency of S. cerevisiae at high temperatures is very low due to increased fluidity in membranes to which the yeast responds by changing its fatty acids composition (Mager and Siderius, 2002; Schuller et al, 2004). Biotic factors induce changes in the gene expression of the guest, giving rise to the synthesis of specific compounds that generate resistance to the strange organism. The objective of this work was to select S. cerevisiae strains capable of fermenting glucose at temperatures above 35°C with an ethanol yield of at least 70% of theoretical value in Fermentation process
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