Fermentation of Sugar by Thermotolerant Hansenula polymorpha Yeast for Ethanol Production

Hansenula polymorpha is a non-conventional and thermo-tolerant yeast that is well-known for its use in the industrial production of recombinant proteins. However, research to evaluate this yeast’s potential for the high-temperature fermentation of sugar to produce alcohols for biofuel applications is limited. The present work investigated a wild-type H. polymorpha strain (DSM 70277) for the production of ethanol at a temperature of 40 °C under limited oxygen presence by using a batch fermentation reactor. Fermentation experiments were performed using three types of sugar (glucose, fructose, xylose) as substrates with two initial inoculum concentrations (1.1 g·L−1 and 5.0 g·L−1). The maximum specific growth rates of H. polymorpha yeast were 0.121–0.159 h−1 for fructose, 0.140–0.175 h−1 for glucose, and 0.003–0.009 h−1 for xylose. The biomass volumetric productivity was 0.270–0.473 g·L−1h−1 (fructose), 0.185–0.483 g·L−1h−1 (glucose), and 0.001–0.069 g·L−1h−1 (xylose). The overall yield of ethanol from glucose (0.470 g·g−1) was higher than that from fructose (0.434 g·g−1) and xylose (0.071 g·g−1). The H. polymorpha yeast exhibited different behavior and efficacy regarding the use of glucose, fructose, and xylose as substrates for producing ethanol. The present knowledge could be applied to improve the fermentation process for valorization of waste biomass to produce bioethanol.