Valorization of lignins from energy crops and agro‐industrial byproducts as antioxidant and antibacterial materials

BACKGROUND Developing eco‐friendly antioxidant and antimicrobial substances originating from biomass residues has recently attracted considerable interest. In this study, two lignosulfonates and various oxidized water‐soluble lignins were investigated for their antioxidant properties, as assessed by ABTS, DPPH and Folin–Ciocalteu methods, and their antimicrobial activity against some bacterial strains responsible for human pathologies. RESULTS The lignosulfonates showed the largest antiradical/antimicrobial capacity, whereas the other substrates were less effective. The observed antioxidant/antibacterial properties were positively correlated with lignin aromatic/phenolic content. The positive correlation between antiradical and antimicrobial activities suggests that lignin scavenging capacity was also involved in its antibacterial activity. A greater antimicrobial performance was generally observed against Gram‐positive bacterial strains, and it was attributed to the intrinsic larger susceptibility of Gram‐positive bacteria to lignin phenols. A significant though lesser inhibitory activity was also found against Escherichia coli. CONCLUSION Our results confirmed the dependence of lignin antioxidant/antibacterial power on its extraction method and chemical structure, as well as on the type of bacterial strains. Identifying the relationship between lignin molecular composition and its antioxidant/antibacterial features represents an advance on the potential future use of renewable and eco‐compatible lignin materials in nutraceutical, pharmaceutical and cosmetic sectors. © 2021 Society of Chemical Industry.