Dual-role cysteine in choline chloride/oxalic acid deep eutectic solvent pretreatment: enzymatic hydrolysis boost via lignin condensation inhibition and cellulose preservation

The redeposition of condensed lignin impedes deep delignification, compromising the saccharification performance of acid pretreated lignocelluloses, while excessive acid hydrolysis of cellulose reduces total glucose recovery. Here, recyclable cysteine was introduced into choline chloride/oxalic acid (ChCl/OA) DES to pretreat bamboo biomass. Cysteine suppressed lignin condensation, preserving 71.8 % of β- O -4 linkages and eliminating pseudo-lignin deposition, thereby increasing lignin removal from 63.9 % to 81.1 %. Simultaneously, cysteine protected cellulose from acid hydrolysis, raising cellulose recovery from 80.0 % to 92.9 %. This dual function reduced surface lignin area by 52.9 %, enhanced cellulose accessibility by 2.3-fold, and increased cellulase adsorption by 64.8 %. Consequently, enzymatic glucose yield surged from 18.6 % to 90.3 %, and total glucose recovery rose from 13.4 % to 75.5 %. This study developed a strategy based on lignin condensation inhibition and cellulose preservation to enhance the saccharification performance of acidic DES pretreated bamboo via adding cysteine.