Hemicellulose degradation: An overlooked issue in acidic deep eutectic solvents pretreatment of lignocellulosic biomass

Deep eutectic solvents (DESs) based pretreatment is an emerging approach to overcome recalcitrance of lignocellulosic biomass and improve its processability. Among different DESs, acidic DESs (ADESs) is popular due to its appealing performance in the biomass fractionation. Most studies concerning ADESs pretreatment focused on cellulose digestibility, as well as understanding lignin properties and its valorization potential, but overlooked the fate of hemicellulose, especially its degradation and loss. Here, the importance of preventing hemicellulose degradation and improving its valorization to the economic viability of ADESs pretreatment was highlighted. Major degradation products derived from hemicellulose and its degradation pathway in ADESs pretreatment are discussed. Finally, factors affecting hemicellulose removal and degradation in ADESs are analyzed and strategies to mitigate its degradation are proposed. The aim of this review is to call for attentions and concerted efforts of designing ADESs pretreatment for minimizing hemicellulose loss and improving the economics of associated biorefinery.