Structural features, chemical composition, antioxidant activities of organosolv lignins extracted from black and white sesame capsules and stalks

Sesame is an industrial crop widely planted in China. Sesame capsules and stalks are by-products of sesame oil production. The production of these byproducts is large, but their utilization rate is low. As lignocellulosic biomass, sesame stalks and capsules contain plentiful amounts of lignin. In this study, the ethanol organosolv method was used to isolate lignin from black sesame capsules (BSL-1) and stalks (BSL-2), and white sesame capsules (WSL-1) and stalks (WSL-2). In order to promote full utilization of these lignins, their structural features and chemical composition were investigated and are here reported for the first time; antioxidant capacities were also analyzed. Among the four lignin fractions, the yield of BSL-1 was highest (53.94%). Capsules (47.04%-53.94%) consistently yielded more lignin than stalks (40.23%–40.90%). The predominant monosaccharides associated with BSL-1, WSL-1, and WSL-2 (i.e., all except BSL-2) were glucose. BSL-2 showed the highest thermal stability with the highest molecular weight. A similar composition ratio of linkages (β-O-4', β-β', and β-5') was observed in BSL-1 and WSL-1, and in BSL-2 and WSL-2. All the lignins belong to the GSH type and had S/G ratio values (2.36–3.05) greater than 2.0. Antioxidant studies showed that BSL-1 had the highest DPPH scavenging activity (RSI = 3.31), WSL-2 had the highest ABTS scavenging activity (RSI = 16.31), and WSL-1 had the highest reducing power values. The current study advances understanding of the structural differences of organosolv lignin from sesame capsules and stalks and should promote their future applications.