2.1. Yeast strain
Kluyveromyces marxianus strain from the collection of the Center of Biomass and Renewable Energy, Chemical Engineering, Diponegoro University (Indonesia), was the yeast strain employed in the experiments. This strain was supplied by Gadjah Mada University (Food and Nutrition Department), Indonesia. Cells of this yeast were maintained at 4o C on potato dextrose agar (PDA) sterilized plates