Improved antioxidant activity of pretreated lignin nanoparticles: Evaluation and self-assembly

Lignin nanoparticles (LNPs) have gained significant attention for their potential as natural antioxidants . This study investigated the effect of various pretreatment methods on the lignin structure and subsequent antioxidant activity of LNPs. Among four pretreated LNPs, hydrothermal LNPs exhibited the highest antioxidant activity , surpassing unpretreated, acid-pretreated and kraft LNPs, with an impressive efficacy of 91.6%. The relationship between LNPs' structure and antioxidant activity was revealed by 2D heteronuclear singular quantum correlation ( 1 H 13 C HSQC) and 31 P nuclear magnetic resonance (NMR). 1 H 13 C HSQC suggested the cleavage of β-O-4 ether bonds, as well as a decrease in ferulic acid and p -coumaric acid, which directly influenced the antioxidant activity of LNPs. 31 P NMR demonstrated a positive correlation between the total hydroxyl group content and the antioxidant activity . Besides, an isothermal kinetic model for scavenging free radicals was established based on Langmuir kinetic model instead of Freundlich model. Moreover, multilayer LNPs, based on layer-by-layer self-assembly, were prepared and exhibited remarkable antioxidant activity of 95.8%. More importantly, when blended with pure cosmetic cream , the multilayer LNPs maintained antioxidant activity of 86.7%. These finding may promote the practical applications of biomolecules, e.g. lignin additives in cosmetics and pharmaceuticals.