Plant‐Based Antioxidant Nanoparticles without Biological Toxicity

Here, we present a function to derive non‐deteriorated nanoparticulated lignin as an antioxidant without biological toxicity that is supplied through the simultaneous enzymatic saccharification and comminution of plants. The lignin exhibits an oxygen radical absorption capacity, even in its macromolecular nature. The non‐deteriorated lignin nanoparticles never inhibit the biological activity of living things, despite their antioxidant nature. The oxygen radical absorption capacity of lignin is dependent on its botanical origin and monomeric structure. A stable organic radical in lignin is responsible for the antioxidant nature of non‐deteriorated lignin. The organic radical of non‐deteriorated lignin, which yields a distinct signal on electron spin resonance spectra, serves as a spin trap reagent that detects the emergence of short lifespan radicals as the change of radical concentration of the lignin. The presented discovery of non‐deteriorated lignin will induce not only the industrial utilization of plant biomass polymers in pharmaceuticals and reagents, but also advance our scientific understanding of the antioxidant function of native lignin.