**9. High-temperature fermentation technologies with thermotolerant yeast**

Currently, biofuel-aimed ethanol fermentation in industry is performed at around 30°C because the most frequently applied yeast is nonthermotolerant *S. cerevisiae*. In the fermentation process, the temperature in the fermenter increases close to a nonpermissible level for the yeast by metabolic and mechanical heat sources. A cooling system with a large amount of water and/or by a cooling unit is equipped for effective fermentation. The cooling cost tends to be higher in tropical countries or increases in summer time in other many countries, and the electricity problem largely affects productivity of ethanol. The HTF using a thermotolerant microbe is expected to provide several advantages. First, it can reduce the cooling cost. Second, the amount of enzyme used for saccharification can be reduced in the simultaneous saccharification and fermentation at higher temperature. Third, higher temperature causes lower contamination by various germs. Fourth, when the distillation under reduced pressure is applied at around 40°C, fermentation and distillation can be performed by one tank, which reduces the manufacturing time and the cost of equipment. Here, we introduce a fundamental research for an energy-saving fermentation technology using thermotolerant yeast.

#### **9.1. Temperature-noncontrolled fermentation with thermotolerant yeast**

For development of the fermentation technology, *K. marxianus* DMKU 3-1042 was used, which efficiently produces ethanol at high temperatures as mentioned above [32, 33]. The utilization of the thermotolerant yeast is favorable to fermentation in a tropical country because it can be performed under temperature-noncontrolled conditions. When a bench-scale fermentation, 2 L of 9% glucose medium, was tested, DMKU 3-1042 produced ethanol equivalent to that under the temperature-controlled condition at 30°C [39]. In a fermenter-scale fermentation with 4000 L of 18% sugarcane, 7% ethanol production was achieved [39].

**Acknowledgements**

**Author details**

Savitree Limtong<sup>4</sup>

Yamaguchi, Japan

Yamaguchi, Japan

Peter Götz<sup>9</sup>

Mochamad Nurcholis<sup>1</sup>

University, Yamaguchi, Japan

University, Chiang Mai, Thailand

Brawijaya University, Indonesia

by Japan Science and Technology Agency.

Tomoyuki Kosaka1,2,3, Noppon Lertwattanasakul<sup>4</sup>

, Ngo Thi Phuong Dung<sup>7</sup>

 and Mamoru Yamada1,2,3\* \*Address all correspondence to: m-yamada@yamaguchi-u.ac.jp

This work was supported by The Core to Core Program, which was granted by the Japan Society for the Promotion of Science, the National Research Council of Thailand, Ministry of Science and Technology in Vietnam, National Univ. of Laos, Univ. of Brawijaya and Beuth Univ. of Applied Science Berlin, supported by Japan Science and Technology Agency, Ministry of Research, Technology and Higher Education of the Republic of Indonesia, Agricultural Research Development Agency of Thailand and Ministry of Science and Technology of Laos as part of the e-ASIA Joint Research Program (e-ASIA JRP), and partially supported by Advanced Low Carbon Technology Research and Development Program, which was granted

, Constantinos Theodoropoulos10, Suprayogi<sup>11</sup>, Jaya Mahar Maligan<sup>11</sup>,

1 Life Science, Graduate School of Science and Technology for Innovation, Yamaguchi

2 Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University,

3 Research Center for Thermotolerant Microbial Resources, Yamaguchi University,

7 Biotechnology Research and Development Institute, Can Tho University, Vietnam

9 Bioprocess Engineering, Beuth University of Applied Sciences, Berlin, Germany

10 School of Chemical Engineering and Analytical Science, Biochemical and Bioprocess Engineering Group, The University of Manchester, Manchester, United Kingdom 11 Agricultural Product Technology Department, Agricultural Technology Faculty,

8 Faculty of Sciences, National University of Laos, Vientiane, Lao PDR

4 Department of Microbiology, Faculty of Science, Kasetsart University, Bangkok, Thailand 5 Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand 6 Center of Excellence in Bioresources for Agriculture, Industry and Medicine, Chiang Mai

, Nadchanok Rodrussamee5,6,

, Masayuki Murata<sup>1</sup>

,

141

, Chansom Keo-Oudone<sup>8</sup>

Potential of Thermotolerant Ethanologenic Yeasts Isolated from ASEAN Countries…

http://dx.doi.org/10.5772/intechopen.79144

#### **9.2. Distillation-connected fermentation with thermotolerant yeast**

As an additional challenge, distillation-connected fermentation was attempted. Because the saturated vapor pressure of ethanol is 177.8 mbar at 41°C, where a thermotolerant microbe can grow well, ethanol can be collected from the fermenting culture when pressure is reduced to less than the saturated vapor pressure. The system shown in **Figure 5** was constructed and tested, which consists of a fermentation and a distillation tank, the primary and secondary ethanol recovery units, a vacuum pump, and a drain unit. In this system, ethanol is concentrated as the process proceeds from the primary to secondary ethanol recovery units. Due to the set-up of this system, the air in the tank was discharged outside during the vacuum distillation, and some ethanol was trapped in the drain unit. When fermentation with *K. marxianus* DMKU 3-1042 and distillation at 70 mbar and 41°C was applied, about 35 and 60% were recovered in the primary and secondary bottles [39]. The process of the simultaneous fermentation and distillation under a low pressure was continuously repeated three times, with 12% rice-hydrolysate [39]. Similar performance was achieved with a thermo-adopted strain of *Zymomonas mobilis* TISTR548, an ethanologenic bacterium [39].

That system provides some benefits: (i) microbes avoid exposure to high concentrations of ethanol or acetic acid or strong oxidative stress and (ii) fermentation can be continued during distillation increasing ethanol yields. Although further experiments for its evaluation are required, the system including HTF is expected to be one of next-generation fermentation technologies.

**Figure 5.** Apparatus for fermentation and distillation under a low pressure. This apparatus consists of a fermentation and distillation tank, primary and secondary recovery bottles, a drain unit, and a vacuum pump.
