Antioxidant and Antibacterial Activities of Sugarcane Bagasse Lignin and Chemically Modified Lignins

Abstract

Unmodified lignin from sugarcane bagasse was chemically modified by acetylation, epoxidation and hydroxymethylation reactions. Modifications in lignin structure were characterized by FT-IR, 1H and 13C NMR spectra. The optimum reaction times for both epoxidation and hydroxymethylation of lignin were found to be 3 h by epoxy content and functional analysis, respectively. Acetylated and epoxy lignins were found to have lower DPPH radical scavenging activity [radical scavenging index (RSI) 0.15 and 0.16] than unmodified lignin (RSI 2.63), whereas hydroxymethyl derivative exhibited comparable activity (RSI 2.70) to unmodified lignin. Lignin and hydroxymethyl lignin were found to be more effective antioxidant than standard 3,5-di-tert-butyl-4-hydroxytoluene all lignins were found to be less effective than standard 3-tert-butyl-4-hydroxyanisole. Epoxy lignin was found to be most effective antibacterial among modified lignins with minimum inhibitory concentrations of 90 and 200 µg/disc against Bacillus aryabhattai and Klebsiella sp., respectively. It was concluded that natural lignin isolated from sugarcane bagasse and chemically modified lignins may be used as potential antioxidants and antibacterials.