Suppressing lignin condensation is crucial for the efficient deconstruction and utilization of lignocelluloses. However, the distinct stabilization behaviors of macromolecular lignin framework and low-molecular-weight lignin fragments remain unclear. How nucleophiles affect residual lignin–cellulase nonproductive adsorption has not been clearly elucidated. In this work, a cysteine-assisted formic acid (FA–Cys) pretreatment was used to separate lignin and improve the saccharification performance of bamboo biomass. Cysteine acted as a sulfur-based nucleophile to intercept reactive benzylic carbocations within the macromolecular lignin framework and aldehyde intermediates generated from β–O–4 cleavage of low-molecular-weight lignin fragments, thereby suppressing lignin condensation. The β–O–4 retention of recovered lignin increased from 25.9% to 89.6%, and the condensed structure decreased from 12.5 to nearly zero per 100 aromatic units. Cysteine decreased the maximum cellulase adsorption capacity of residual lignin from 10.5 to 4.5 mg/g, while excessive cysteine addition increased the adsorption capacity. High lignin removal (92.6%) and mitigated nonproductive adsorption of residual lignin resulted in an increase in glucose yield of FA–Cys-pretreated bamboo from 58.7% to 98.9%. This study advances the understanding of how nucleophiles suppress lignin condensation, providing a theoretical basis for the efficient separation of noncondensed lignin and enhanced cellulose saccharification of bamboo.
Ying et al. (Fri,) studied this question.