Demethylation of ethanol organosolv lignin by Na2SO3 for enhancing antioxidant performance

Natural polyphenol antioxidants have excellent antioxidant activity and degradability which are considered as one of the possible alternatives to chemical synthetic antioxidants. Here, lignin-based polyphenols were prepared from poplar lignin, pine lignin and rice husk lignin by demethylation, and no toxic reagents were used in the preparation process. The phenolic hydroxyl groups of all three lignin were increased and the methoxyl content was significantly reduced after the demethylation without degradation or structural changes in the lignin as shown by GPC and 2D HSQC analyses. Furthermore, the antioxidant activity of the modified lignin was significantly increased. In this paper, a green and efficient strategy was developed to prepare lignin-based polyphenols with high phenolic hydroxyl content, low molecular weight, strong antioxidant activity and low cytotoxicity, which have a promising future in the field of antioxidant applications.