Antioxidant Activity and Pyrolysis Properties of Lignin Extracted from Camellia oleifera Shell by Deep Eutectic Solvents (DES)

In order to obtain lignin with low molecular weight and polydispersity, as well as high antioxidant activity, using Camellia oleifera shell as raw material, four lignin products were isolated from it by alkaline and deep eutectic solvents. The structural and pyrolysis properties of lignin were investigated with ultraviolet spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC) and thermogravimetric analyzer (TGA). Furthermore, the antioxidant activity of the lignin samples was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity assay. The UV and FTIR analyses showed that the lignin from Camellia oleifera shell was mainly composed of guaiacyl and syringyl. GPC analysis revealed that AL had a relatively higher molecular weight (Mw=41858 g/mol) and broad polydispersity index (PDI=4.53), and the DES-lignin exhibited relatively low relative molecular weight (Mw<11000 g/mol) and narrow polydispersity index (PDI<2). Thermogravimetric analysis showed that the thermal stability of lignin samples was ChCl-OA>AL>ChCl-EG-P>ChCl-GA. Furthermore, the results showed that four lignin products had good antioxidant activity in vitro, and the IC₅₀ values of DPPH free radical scavenging ability was 0.388~1.02 mg/mL. The findings of this study would provide a novel way to fractionate lignin from Camellia oleifera shell, and provide certain reference value for the development of lignin valorization.