Fermentation of sunflower seed hull hydrolysate to ethanol by Pichia stipitis

Ethanol production from sunflower seed hull hydrolysate was evaluated using Pichia stipitis NRRL Y-7124. The hydrolysate prepared with 0.7 M H2SO4 at 90 °C was fermented as substrate in shaking bath experiments at 30 °C. In a group of experiments, the influence of various detoxification methods on the fermentability of hydrolysate was investigated at pH 6. Even though the ability of all employed pretreatments to enhance fermentation performance was close, the sequential application of overliming with sodium sulfite addition was the best detoxification method. Additional experiments were performed with detoxified hydrolysate to investigate the effect of shaking rate (70–130 rpm) and initial pH (5.5–7) on the fermentation. The highest ethanol level 11 g L−1 was achieved at initial pH of 6 and 100 rpm shaking rate from a hydrolysate containing 48 g L−1 total reducing sugar. The corresponding alcohol yield and volumetric productivity were 0.32 g g−1 and 0.065 g L−1 h−1.