Acidic and alkaline deep eutectic solvents (DESs) pretreatment of grapevine: Component analysis, characterization, lignin structural analysis, and antioxidant properties

Deep eutectic solvents (DESs) have been extensively applied to pretreat lignocellulose; however, comparative research on acidic and alkaline DES pretreatment is relatively lacking. Herein, pretreatment of grapevine agri-cultural by-products with seven DESs were compared in terms of removal of lignin and hemicellulose and component analysis of the pretreated residues. Among the tested DESs, both acidic choline chloride-lactic (CHCl-LA), and alkaline potassium carbonate-ethylene glycol (K2CO3-EG) were effective in delignification. Thereafter, the CHCl-LA and K2CO3-EG extracted lignin was compared by analyzing their physicochemical structure changes and antioxidant properties. The results showed that the thermal stability, molecular weight, and phenol hydroxyl percentage of CHCl-LA lignin were inferior to K2CO3-EG lignin. It was found that the high antioxidant activity of K2CO3-EG lignin was mainly attributed to the abundant phenol hydroxyl, guaiacyl (G), and para-hydroxy-phenyl (H). By comparing acidic and alkaline DES pretreatments and their lignin nuances in biorefining, novel insights are derived for the scheduling and selection of DES for lignocellulosic pretreatment.

Automated summary

This study compared the pretreatment effects of seven deep eutectic solvents (DESs) on grapevine agricultural by-products, with a focus on the removal of lignin and hemicellulose and the analysis of the pretreated residues. The results showed that both acidic choline chloride-lactic (CHCl-LA) and alkaline potassium carbonate-ethylene glycol (K2CO3-EG) were effective in delignification, but the lignin extracted by CHCl-LA had inferior physicochemical properties compared to K2CO3-EG lignin. It was found that the high antioxidant activity of K2CO3-EG lignin was mainly due to the abundant phenol hydroxyl, guaiacyl (G), and para-hydroxy-phenyl (H) groups.