The Remarkable Role of Extractable Lignin in Enhancing Enzymatic Hydrolysis of Organosolv Pretreated Biomass

The interactions between lignin and cellulase enzymes play a critical role in the effective enzymatic hydrolysis of lignocellulosic biomass. Organosolv pretreatment has shown great potential for producing lignocellulosic substrates from softwood and hardwood with good digestibility. The objective of this work was to investigate the role of extractable lignin in the enzymatic hydrolysis of ethanol organosolv pretreated sweetgum (OPSG).  We removed the extractable lignin in OPSG by ethanol washing and 1% NaOH , then compared the enzymatic hydrolysis performance. Interestingly , we found that removing extractable lignin in OPSG showed an adverse effect on enzymatic hydrolysis. The hydrolysis yield dropped from 70.6% (washing only with water) to 55.5% (washing with 95% ethanol). Removing extractable lignin in OPSG with 1% NaOH also reduced the final hydrolysis yield from 69.9% to 43.8%. Furthermore , when we added extractable lignin into the hydrolysis of Avicel , and the hydrolysis yield increased from 67.6% to 71.7%. It indicated extractable lignin in pretreated substrates potentially facilitated the enzymatic hydrolysis. However , the bulk lignin still limited the enzymatic hydrolysis significantly; removing bulk lignin increased the hydrolysis yield by 49%. Therefore , we believe that extractable lignin and bulk lignin probably play remarkably different roles in enzymatic hydrolysis , and extractable lignin can assist the enzymatic hydrolysis.