Organic solvent fractionation of acetosolv palm oil lignin: The role of its structure on the antioxidant activity

Pressed palm oil mesocarp fibers (PPOMF) are by-products from oil palm industry and represents a potential source of lignocellulosic biomass. In order to add value to this agro-waste, dewaxed palm oil acetosolv lignin (DPOAL) was extracted under eco-friendly pulping method. The chemical composition and structural characteristics of DPOAL were investigated. The results showed elevated yield (48.5%) and high purity (94.3%), besides a moderate average molecular weight (1394 g mol(-1)) and narrow polydispersity index (1.88). Structural characterization via FT-IR, H-1-C-13 HSQC and P-31 NMR indicated that DPOAL was a typical HGS-type lignin. In addition, to increase the phenolic hydroxyl contents and improve DPOAL's antioxidant properties through a simple method, a fractionation process with methanol, ethanol and acetone was carried out, obtaining the methanol (MeOH-F), ethanol (EtOH-F) and acetone (ACT-F) soluble fractions. These were characterized by FT-IR, DSC, H-1-C-13 HSQC and P-31 NMR, which showed higher values of phenolic and aliphatic hydroxyls groups compared to DPOAL. The antioxidant activity was evaluated by the free radical scavenging activity of 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH.) and compared with commercial antioxidants, such as BHT and Irganox 1010. Interestingly, lignin samples had significantly lower IC50 values compared to commercial antioxidants, what suggests a great potential as novel natural antioxidant. (C) 2018 Elsevier B.V. All rights reserved.