Fractionation of enzymatic hydrolysis lignin by sequential extraction for enhancing antioxidant performance

- Four lignin fractions with different molecular weight were obtained by sequential extraction.
- Total phenolics and methoxyl content of lignin increased with decrease of molecular weight.
- Dichloromethane fraction lignin with lowest molecular weightM¯w showed the highest antioxidant activity.
- Phenolic hydroxyl and methoxyl content had positive effect on free radical scavenging activity.
- Sequential extraction achieved a remarkable improvement in lignin antioxidant performances.

The heterogeneity of lignin chemical structure and molecular weight results in the lignin inhomogeneous properties which also covers the antioxidant performance. In order to evaluate the effects of lignin heterogeneity on its antioxidant activity, four lignin fractions from enzymatic hydrolysis lignin were classified by sequential organic solvent extraction and further evaluated by DPPH (1,1-Diphenyl-2-Picrylhydrazyl) free radical scavenging capacity and reducing power analysis. The characterization including FTIR, 1H NMR and GPC showed that the fractionation process could effectively separate lignin fractions with distinctly different molecular weight and weaken the heterogeneity of unfractionated lignin. The antioxidant performance comparison of lignin fractions indicated that the dichloromethane fraction (F1) with lowest molecular weight (4585 g/mol) and highest total phenolics content (246.13 mg GAE/g) exhibited the highest antioxidant activity whose value was close to commercial antioxidant BHT (butylated hydroxytoluene). Moreover, the relationship between the antioxidant activity and the structure of lignin was further discussed to elucidate the mechanism of antioxidant activity improvement of lignin fractionation. Consequently, this study suggested that the sequential extraction was an effective way to obtain relatively homogeneous enzymatic hydrolysis lignin fractions which showed the potential for the value-added antioxidant application.

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