Ethanol fermentation of red oak acid prehydrolysate by the yeast Pichia stipitis CBS 5776

Abstract

Xylose, the dominant sugar in red oak acid prehydrolysate, was fermented to ethanol. In batch cultures of xylose concentrations ranging from 10 to 100 g l −1, Pichia stipitis CBS 5776 yielded 0.50–0.40 g ethanol per g xylose consumed. Model compounds of inhibitors generated in the acid prehydrolysis of red oak hemicelluloses, lignin and extractives, hindered the fermentation. Recycled yeasts and treatments with molecular sieve or mixed bed ionresins facilitated the ethanol fermentation of red oak acid prehydrolysate. A maximal ethanol concentration of 9.9 g l −1 was obtained from an acid prehydrolysate containing 21.7 g l −1 of xylose. Fermentation inhibitors derived from red oak lignin and extractives were identified.