Abstract: Lignin was extracted from sunflower seed shell using acetic acid. The structural features of the isolated lignin were characterized by gel permeation chromatography (GPC), ultraviolet spectroscopy (UV), infrared spectroscopy (FT-IR), hydrogen-1 nuclear magnetic resonance spectrocopy (1H-NMR) and thermogravimetry (TG). In addition, the antioxidant activity of the lignin was evaluated by 1,1 diphenyl-2-trinitrobenzene hydrazine (DPPH) radical scavenging activity assay. The results showed that the yield and purity of lignin extracted from sunflower seed shell were 70.12% (based on Klason lignin) and 88.54%, respectively, and the content of lignin-associated carbohydrates was 2.92%. The lignin was GS-type lignin with β-O-4 ether bond as the major inter-unit linkage, having a high proportion of guaiacyl (G) units. The weightaverage molecular (Mw), number-average molecular (Mn) and polydispersity (Mw/Mn) of the lignin were 2 977, 1 931 D and 1.54, respectively. It major decomposition temperature was 200–400 ℃ and the maximum weight loss rate was 0.32%/℃. We found that the lignin showed stronger antioxidant activity than butylated hydroxytoluene (BHT) with free radical scavenging index (RSI) of 1.54 versus 0.94. The results suggested that acetic acid extraction provides a promising way to prepare lignin from sunflower seed shell with a good potential as an antioxidant in food and other industries.

Key words: sunflower seed shell, acetic acid extraction, lignin, structural feature, antioxidant activity