International Journal of Applied Science and Technology Vol. 2 No. 4; April 2012 65 Screening Useful Isolated Yeasts for Ethanol Fermentation at High Temperature Dung, Ngo Thi Phuong Biotechnology Research and Development Institute Can Tho University Can Tho City, Vietnam Pornthap Thanonkeo Department of Biotechnology, Faculty of Technology Khon Kean University Khon Kean, Thailand Huynh Xuan Phong Biotechnology Research and Development Institute Can Tho University Can Tho City, Vietnam Abstract Due to a current challenge of increasing global temperature, thermo-ethanologenic yeasts receive considerably interest nowadays. In this study, 11 of 31 yeast isolates selected from the previous research based on their well growth at temperature up to 45°C were tested for fermentative capacity and ethanol tolerance at high temperatures. Five isolates BM2, BM3, HX1, C2 and V2 performed significantly well (at the 95% confidence level) in fermentation at 40°C. Of which BM3, BM2, HX1 and C2 were able to tolerate up to 15% v/v ethanol. After 5 days of fermentation at high temperature (40 o C), the highest fermentation yield of yeasts could reach up to 76% and this was found in fermentation from saccharified glutinous rice liquid, indicating the further application feasibility of these yeasts for ethanol production at high temperature. Four selected target yeasts were characterized as follow: HX1: Candida tropicalis , BM3: Torulaspora globosa , both C2 and BM2: Pichia kudriavzevii . Key words: Ethanol, ethanol tolerance, fermentation, thermo-tolerance, yeast. 1. Introduction Ethanol is an important industrial chemical with emerging potential as a bio-fuel to replace non-renewable fossil fuels (Alfenore et al., 2002). The increasing demand of ethanol production for various industrial purposes such as alternative source of energy, industrial solvents, cleansing agents and preservatives, has necessitated increased production of this alcohol. Developing and utilizing of ethanologenic microorganisms can obviously lead to success in large-scale ethanol manufacture. Ethanol production is usually accomplished by chemical synthesis of petrochemical substrates and microbial conversion of carbohydrates present in agricultural products by yeasts. The tolerant ability of yeasts under the conditions of high temperature and high ethanol levels (Ansanay-Galeote et al., 2001; Osho et al., 2005) during fermentation process is becoming an increasingly important characteristic that attracts many researchers as there has been a mixed variety of benefits which could be exploited through the use of thermophilic yeasts for ethanol production. Thermo-tolerant yeasts are capable of growth and fermentation during the summer months in non-tropical countries and under tropical climates as well. Cooling costs during the process of ethanol production are expensive; hence, by using thermo-tolerant yeasts, cooling and distillation costs can be reduced. Besides, higher saccharification and fermentation rates, continuous ethanol removal and reduced contamination have stimulated a search for routes to thermo-tolerant yeasts. With the aim to pave the way for application of useful thermo- and ethanol tolerant yeasts for ethanol production, selected yeast isolates were tested and characterized for their fermentative performance at high temperature and their ethanol tolerance. ______________ This research was partly sponsored by Can Tho University and JSPS-NRCT Asian Core Program