Composition and structure of an antioxidant acetic acid lignin isolated from shoot shell of bamboo (Dendrocalamus Latiforus)

Bamboo shoot shell (BSS), which contains a large amount of insoluble fibre and lignin, is the main agricultural waste from the production of bamboo shoots. To utilize this waste in a value-added manner, the acetic acid lignin (AL) fraction from BSS was extracted via a combination of hot water pre-treatment and acetic acid post-treatment in the present study. The chemical composition, structural characteristics, and antioxidant activity of AL were investigated and compared to the corresponding milled wood lignin (MWL). The results showed that AL had a higher yield (74%) and lower content of associated carbohydrates (2.96%) than MWL (5.16%). GPC analysis revealed that AL possessed a moderate molecular weight (M-w = 2789 Da) and narrow polydispersity index (M-w/M-n = 1.54). Structural characterization via FT-IR, H-1 NMR, 2D-HSQC, and 31 P NMR indicated that AL from BSS was a typical HSG-type lignin and was partially acylated at the beta-carbon of the side chain by p-coumarate. Moreover, the bonds between lignin units were predominately beta-O-4' linkages. Compared to MWL, AL possessed a characteristically higher phenolic hydroxyl group content and S/G ratio. In terms of the DPPH radical scavenging activity, ABTS radical cation scavenging activity and ferric reducing antioxidant power, AL showed stronger antioxidant activity than MWL and was superior to the commercial synthetic antioxidant BHT. In summary, by applying a modified two-step procedure, which included hot water pre-treatment and acetic acid extraction, AL from BSS was effectively extracted, and the antioxidant potential of AL was characterized. (C) 2016 Elsevier B.V. All rights reserved.