(602c) Inhibitory Effect of Hemicellulose Hydrolysates on Glucose Transport across Cell Membrane in Yeast Fermentation

Biomass pretreatment generates a wide range of toxic compounds from lignin and sugars degradation. These toxic compounds significantly inhibit cell growth and production rate in microbial fermentation. Phenolic aldehydes and ketones have been suggested to the most toxic compounds to microbes. However, the mechanism of inhibition has not been elucidated. Glucose transport across the yeast cell membrane typically is mediated by specific membrane carriers. The effect of hemicellulose hydrolysates on glucose transport and cell-free fermentation with yeast was studied. Unexpectedly, it was observed that cell-free yeast extracts consumed all the glucose in the undetoxifed hydrolysates within 12 h and produced 9.5 g/l of ethanol, but the intact yeast could not ferment the undetoxifed hydrolysates. It was also noticed that no intracellular glucose was detected in yeast after incubation with the undetoxifed hydrolysates, while 46 mg/g intracellular glucose was presented inside of yeast after incubation with the detoxified hydrolysates. The volumetric ethanol productivity was correlated very well with the intracellular glucose concentration. This study indicated that the toxic compounds mainly inhibit the glucose transport step, but not the fermentation step in yeast or bacteria.