Revealing enzymatic digestibility of kraft pretreated larch based on a comprehensive analysis of substrate-related factors

Abstract

The high degree of lignification in larch shows strong recalcitrance for its enzymatic digestibility to produce fermentation sugars for the further bio-energy production. Hence, pretreatment with excellent delignification ability should be carried out for larch. In this work, a high delignification degree of 77.3% could be achieved for larch after kraft pretreatment, while it still had a low enzymatic digestibility (30.3%), which was due to the remained stout cell wall structure revealed by confocal laser scanning microscopy. To elucidate the reason for low enzymatic digestibility, the addition of bovine serum albumin (BSA) and ball-milling were performed to investigate the substrate-related inhibiting factors of lignin and cellulose, respectively. It is found that the enzymatic digestibility of pretreated larch was enhanced to 58.8% by the addition of BSA, which is due to the reduction of the non-productive binding between residual lignin and cellulases. In addition, ball-milled could disrupt the cellulose's crystalline structures, which enhance the enzymatic hydrolysis of BSA-absorbed larch to 77.7%. This result indicated that cellulose structure is another inhibition bastion towards enzymatic digestion. This work revealed the effect of substrate-related factors that restrict the enzymatic digestibility of larch.