葵花籽壳木质素的结构分析及抗氧化活性

以葵花籽壳为原料,采用醋酸法提取木质素,并利用凝胶渗透色谱、紫外光谱、傅里叶变换红外光谱、核磁共振氢谱和热重分析对提取的木质素进行结构表征,并对提取木质素的抗氧化活性进行评价。结果表明:醋酸法木质素提取率为70.12%(相对于Klason木质素),纯度达到88.54%,结合少量的碳水化合物(2.92%)。葵花籽壳木质素为GS型木质素,含有较高的愈创木基结构单元(G),结构单元之间的连接键以β-O-4结构为主,重均分子质量(M_w)、数均分子质量(M_n)和多分散度(M_w/M_n)分别为2 977、1 931 D和1.54。葵花籽壳醋酸提取的木质素主要降解温度在200~400℃之间,最大失质量速率为0.32%/℃。抗氧化活性研究表明,木质素清除1,1-二苯基-2-三硝基苯肼自由基指数值为1.54,显著高于商业合成抗氧化剂二丁基羟基甲苯(0.94),具有很好地应用于食品及其他工业做抗氧化剂的前景。

Structural Features and Antioxidant Activities of Lignin Extracted from Sunflower Seed Shell

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.