Ethanol organosolv lignin from different agricultural residues: Toward basic structural units and antioxidant activity

The growing interest in the substitution of synthetic food antioxidants by natural ones has fostered research on vegetable sources and the screening of raw materials for identifying new antioxidants. Special attention is focused on their extraction from inexpensive or residual sources from agricultural industries. Herein, the antioxidant activities of lignin obtained from 4 residual sources were investigated. The obtained lignin samples were characterized by different analytical techniques evaluating their chemical structure, phenolic content, thermal behavior and molecular weight. The antioxidant activity of the analyzed lignins was evaluated by the DPPH assay, the radical ABTS assay, and trivalent iron reduction method. It was found t that lignin antioxidants could scavenge free radicals and reduce oxidants. The high correlation between antioxidant capacity and its total phenol content indicated that phenolic hydroxyl groups were the main contributors to these lignins' antioxidant activity.