Unmasking the Recalcitrance of Hardwoods and Methods for Improving AFEXTM Pretreatment Effectiveness

The thickness of the wood cell wall makes it highly resistant to enzyme penetration and requires a pretreatment that significantly increases the porosity and enzyme access to carbohydrates. Ammonia pretreatments are rather ineffective at increasing the digestibility of hardwoods in part due to an inability to break linkages and remobilize components within the plant cell wall. One possibility is that the lignin is too highly cross-linked and is not sufficiently disrupted by AFEX^TM* (ammonia fiber expansion) pretreatment. In order to investigate whether altering the lignin structure and reducing cross-linking is sufficient to significantly increase yields, we pretreated transgenic poplar that had been F5H-upregulated and contained highly linear lignin with >95% syringyl subunits and evaluated whether lignin extraction is feasible or can improve yields from these materials. In a further attempt to increase yields from hardwoods, we also investigated the possibility of replacing ammonia with volatile amines during the AFEX^TM process as well as the feasibility for lignin extraction and cellulose III activation. 

*AFEX^TM is a registered trademark of MBI International, Lansing, MI USA.