Valorization of Acid Isolated High Yield Lignin Nanoparticles as Innovative Antioxidant/Antimicrobial Organic Materials

Abstract

In this study, dissolution of pristine alkali lignin into ethylene glycol, followed by addition of different acidic conditions (HCl, H2SO4, and H3PO4 at different pH) has been considered as a simple method to prepare high yield lignin nanoparticles (LNP). Field emission scanning electron microscopy (FESEM), Zeta potential, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA) have been utilized to determine the influence of the precipitation procedures on particle size, Zeta potential, molecular weight, and thermal stability of final obtained LNP. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) were also considered to investigate the influence of lignin chemical structures and composition on its antioxidative and antimicrobial behaviors. Results from DPPH (1,1-diphenyl-2-picryl-hydrazyl) activity revealed the antioxidant response of LNP aqueous solutions, whereas results from antimicrobial tests confirmed LNP as effective antibacterial agents against Gram negative bacteria Pseudomonas syringae pv tomato (CFBP 1323) (Pst), Xanthomonas axonopodis pv vesicatoria (CFBP 3274) (Xav), and Xanthomonas arboricola pv pruni (CFBP 3894) (Xap) plant pathogen strains. The results confirmed how high efficient antioxidant and antimicrobial LNP could be considered as an easy methodology for plant pathogens control. LNPs penetrate the cell wall by its lysis and react with ROS species inducing oxidative stress, ATP depletion, and decrease in intracellular pH of plant bacteria.