Abstract
Ethanol production at elevated temperatures requires high potential thermotolerant ethanol-producing yeast. In this study, nine isolates of thermotolerant yeasts capable of growth and ethanol production at high temperatures were successfully isolated. Among these isolates, the newly isolated thermotolerant yeast strain, which was designated as Saccharomyces cerevisiae DBKKU Y-53, exhibited great potential for ethanol production from sweet sorghum juice (SSJ) at high temperatures. The maximum ethanol concentrations produced by this newly isolated thermotolerant yeast at 37 °C and 40 °C under the optimum cultural condition were 106.82 g·L−1 and 85.01 g·L−1, respectively, which are greater than values reported in the literatures. It should be noted from this study with SSJ at a sugar concentration of 250 g·L−1 and an initial pH of 5.5 without nitrogen supplementation can be used directly as substrate for ethanol production at high temperatures by thermotolerant yeast S. cerevisiae DBKKU Y-53. Gene expression analysis using real-time RT-PCR clearly indicated that growth and ethanol fermentation activities of the thermotolerant yeast S. cerevisiae DBKKU Y-53 at a high temperature (40 °C) were not only restricted to the expression of genes involved in the heat-shock response, but also to those genes involved in ATP production, trehalose and glycogen metabolism, and protein degradation processes were also involved.
Highlights
Bioethanol is a clean, renewable, environmental friendly source of fuel energy that can be produced from different feedstocks and conversion technologies
The results showed that nine isolates of yeast, which were designated as DBKKU Y-53, DBKKU Y-55, DBKKU Y-58, DBKKU Y-102, DBKKU Y-103, DBKKU Y-104, DBKKU Y-105, DBKKU Y-106, and DBKKU Y-107, were able to grow and produce a relatively high level of ethanol at 45 ̋ C
Materials in and Utilization of high-potential thermotolerant ethanol-producing yeast is a promising approach to reduce the energy used in cooling systems and to reduce the operating cost of ethanol production at high temperatures
Summary
Bioethanol is a clean, renewable, environmental friendly source of fuel energy that can be produced from different feedstocks and conversion technologies. It is one of the most promising substitutes for fossil energy and has high potential to replace petroleum-based fossil fuels [1,2,3]. Moench) is one of the most promising sugar crops for industrial bioethanol production It is a C4 plant, is similar to sugarcane, and belongs to the grass family. Sweet sorghum has a short growing period (3–4 months) It can be planted two or three times a year. Sweet sorghum is considered as an important food resource in some countries, such as India, China, which uses sweet sorghum juice (SSJ) to produce syrup, the Thai government promotes sweet sorghum to be used as an energy crop for large-scale ethanol production together with sugarcane and cassava
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