The influence of bark on the fermentation of Douglas-fir whitewood pre-hydrolysates

Abstract.

Douglas-fir (Pseudotsuga menziesii) whitewood was supplemented with increasing concentrations of bark (0–30%) and was pretreated using SO₂-catalysed steam explosion. The presence of bark in the feedstock resulted in the decreased recovery of total sugars, furfural and 5-hydroxymethylfurfural in the resultant pre-hydrolysate. No detrimental impact on monomer sugar recovery was observed. The concentration of lipophilic extractives present in the pre-hydrolysate increased with increasing bark loading, to a maximum of 0.43 g l^–1. The water-soluble pre-hydrolysates were fermented by Saccharomyces cerevisiae to determine the impact of bark on sugar consumption and ethanol production. Despite the inclusion of bark, fermentation of all pre-hydrolysates resulted in the complete consumption of hexose sugars within 48 h. Ethanol yields were greater than 0.43 g g^–1 for all pre-hydrolysates regardless of bark content, indicating that, up to a content of 30%, bark had a negligible impact on the fermentation of the pre-hydrolysates to ethanol.