Cellulose esterification with carboxylic acid in deep eutectic solvent pretreatment inhibits enzymatic hydrolysis

Avicel cellulose was pretreated using two commonly used carboxylic acid-based deep eutectic solvents, i.e., choline chloride-lactic acid and choline chloride-formic acid. The pretreatment process resulted in the formation of cellulose esters with lactic acid and formic acid, which was confirmed by infrared and nuclear magnetic resonance spectra. Surprisingly, the esterified cellulose led to a significant decrease in the 48-h enzymatic glucose yield (>= 75%) compared to raw Avicel cellulose. Analysis of changes in cellulose properties caused by pretreatment, including crystallinity, degree of polymerization, particle size and cellulose accessibility, contra-dicted the observed decline in enzymatic cellulose hydrolysis. However, removing the ester groups through saponification largely recovered the reduction in cellulose conversion. The decreased enzymatic cellulose hy-drolysis by esterification may be attributed to changes in the interaction between cellulose-binding domain of cellulase and cellulose. These findings provide valuable insights into improving the saccharification of ligno-cellulosic biomass pretreated by carboxylic acid-based DESs.

Automated summary

Avicel cellulose was pretreated with two commonly used carboxylic acid-based deep eutectic solvents, choline chloride-lactic acid and choline chloride-formic acid. The pretreatment led to the formation of cellulose esters with lactic acid and formic acid, which was confirmed through spectroscopic analysis. Surprisingly, the esterified cellulose showed a significant decrease in enzymatic glucose yield compared to the untreated cellulose, but this reduction could be recovered by removing the ester groups through saponification. The decreased enzymatic cellulose hydrolysis may be attributed to changes in the interaction between the cellulose-binding domain of cellulase and the esterified cellulose.