Preparation and characterisation of lignin nanoparticles: evaluation of their potential as antioxidants and UV protectants

Lignin, an abundant plant biopolymer, is known to possess antioxidant and UV protectant properties in its native state. Nanoparticles exhibit either improved or different properties corresponding to their bulk materials or parent polymers. In the present study, using nanoprecipitation method, dioxane lignin nanoparticles (DLNP) and alkali lignin nanoparticles (ALNP) are fabricated from two different sources of lignin, i.e., hardwood dioxane lignin (DL) extracted from subabul stems and softwood alkali lignin (AL) which is available as a commercial source. Both DLNP and ALNP were fabricated in spherical shape with mean size of 80-104 nm. Analysis of radical scavenging activity revealed that both DLNP and ALNP possess higher antioxidant activity when compared with their parent polymers DL and AL, respectively. UV protectant potential of DLNP and ALNP was validated by monitoring the survival rates of Escherichia coli upon UV-induced mortality. DLNP and ALNP were more efficient than DL and AL in protecting E. coli against UV-irradiation-induced mortality. However, upon irradiation for different time periods, DLNP offered pronounced protection for E. coli against UV when compared with ALNP. Thus, the present study demonstrates that the antioxidant and UV protection properties of DLNP can be exploited further in food, pharmaceutical and cosmetic industries.