# Evaluation of Acidic Deep Eutectic Solvents Treatment on Enzymatic Hydrolysis Lignins: Structural Analysis and Antioxidant Activity

## TL;DR

This study explores how acidic deep eutectic solvents improve the antioxidant activity and UV absorption of lignin from enzymatic hydrolysis.

## Contribution

The novel contribution is demonstrating that DES treatment enhances lignin's antioxidant properties and structural characteristics.

## Key findings

- Treatment with DESs preserved the aromatic structure of EHL and increased its O/C atomic ratio.
- DEHL showed reduced UV transmittance and increased phenolic hydroxyl content, especially when treated with ChCl–p-toluenesulfonic acid.
- ChCl–p-toluenesulfonic acid-treated DEHL had the highest antioxidant activity with an IC50 DPPH value of 262.87 μg/mL.

## Abstract

The high-value utilization of enzymatic hydrolysis lignin (EHL) is essential for promoting the development of the biorefinery industry. This study investigated the enhancement of the antioxidant activity and ultraviolet (UV) absorption capacity of EHL through treatment with choline chloride (ChCl)-based acidic deep eutectic solvents (DESs). The yield, chemical structure, UV absorption properties, antioxidant activity, and thermal stability of the degraded and regenerated enzymatic hydrolysis lignin (DEHL) were analyzed. The results indicated that treatment with DESs effectively preserved the aromatic structure of EHL. Compared to untreated EHL, DEHL exhibited an increased O/C atomic ratio, a decreased UV transmittance, a significant reduction in weight-average molecular weight (Mw), and a notable increase in phenolic hydroxyl (ArOH) content. Notably, DEHL treated with ChCl–p-toluenesulfonic acid had the lowest Mw (1586 g/mol) and the highest ArOH content. Except for the ChCl–malic acid and ChCl–acetic acid systems, all the other five DES treatments enhanced the antioxidant activity of DEHL to varying degrees. Among them, DEHL treated with ChCl–p-toluenesulfonic acid exhibited the highest antioxidant activity, with an IC50 DPPH value of 262.87 μg/mL.