Background:
Hemicellulose is often credited with being one of the important physical barriers to enzymatic hydrolysis of cellulose by blocking enzyme access to the cellulose surface. In addition to that, our recent research suggested that hemicelluloses, particularly in the form of xylan and its oligomers, can more strongly inhibit cellulase activity than glucose and cellobiose. Removal of hemicelluloses or elimination of their negative impacts can, therefore, become especially pivotal to achieving higher cellulose conversion with lower enzyme doses.
Results:
In this study, cellulase was supplemented with xylanase and beta-xylosidase to boost conversion of both cellulose and hemicellulose in pretreated biomass through conversion of xylan and xylooligomers to less inhibitory xylose. Although addition of xylanase and beta-xylosidase did not necessarily enhance Avicel hydrolysis, glucan conversions increased by 27% and 8% for AFEX and dilute acid pretreated corn stover, respectively. In addition, adding hemicellulase several hours prior to adding cellulase was more beneficial than later addition, possibly as a result of a higher adsorption affinity of cellulase and xylanase to xylan than glucan.
Conclusions:
This key finding elucidates a possible mechanism for cellulase inhibition by xylan and xylooligomers and advances the need to optimize the enzyme formulation for each pretreated substrate. More research is needed to identify advanced enzyme systems designed to hydrolyze different substrates with the maximum overall enzyme efficacy.