The potential of lignin extracts from sugarcane bagasse to scavenge reactive oxygen and nitrogen species

Lignins are by-products from biomass-based industries, non-toxic, inexpensive and available in large amounts. Due to the high content of diverse functional groups and its phenylpropanoic structure, lignin can act as a strong antioxidant. However, the scavenger capacity of the lignin depends on the plant species, as well as the extraction and separation processes for lignin fractionation. The aim of this work was to evaluate the antioxidant capacity of lignin extract produced after steam explosion and alkaline treatment of sugarcane bagasse (AT) and the supernatant produced after acid precipitation of AT, dubbed as lignin waste fraction (WL). The total phenolic content and the scavenge capacity against reactive oxygen (ROO^● and H₂O₂) and nitrogen (ONOO^-) species of soluble fractions of AT obtained at different pH values (12, 10, 8, 6, 4 and 2) and of WL were evaluated. The chemical characterization was performed by UV, FT-IR and GC-MS/MS and H-NMR. AT-pH2 and WL exhibited the highest scavenging capacities against all species tested (10,17 ± 0,7 mmol TE.g^-1 of lignin and 11,45 ± 1,28 mmol TE.g^-1 of lignin for ROO^●, IC₃₀=14,9 µg.mL^-1 and IC₃₀=16,6 µg.mL^-1 for H₂O₂, and IC₅₀₌2,27 µg.mL^-1 and IC₅₀₌1,61 µg.mL^-1 for ONOO^-, respectively). These two lignin fractions also showed lowest content of phenolic hydroxyl groups, along with molecules with lower molecular weight, when comparing with other fractions.  Thus, suggesting that WL and AT-pH2 have potential for development of value-added applications, in particular in pharmaceutical and food industries.