Conversion of Beech Wood into Antiviral Lignin–Carbohydrate Complexes by Microwave Acidolysis
Ruibo Li, Ryota Ouda, Chihiro Kimura, Ryo Narita, Hiroshi Nishimura, Takashi Fujita, Takashi Watanabe
Abstract
Virus pandemics pose a threat to human life. In this study, we developed a simple method for the conversion of woody biomass into antiviral substances. Beech wood was decomposed by microwave acidolysis in 0.5% aq H2SO4 and fractionated by silica gel chromatography. The obtained fractions exhibited strong antiviral activity against encephalomyocarditis virus (EMCV) without cytotoxicity. Structural analyses revealed that the separated antiviral substances were lignin–carbohydrate complexes with molecular weight in the range of 2600–3900, containing 86.8–90.4% lignin and 3.1–6.1% carbohydrates. Moreover, the native β-O-4 linkages were considerably cleaved by microwave acidolysis, whereas the β–β and β-1 interlinkages remained partially unchanged. A signal corresponding to the α-ether linkage between the lignin and carbohydrates was observed in the heteronuclear single-quantum coherence nuclear magnetic resonance spectra. The cleavage of the carbohydrate chains by hemicellulase significantly reduced the antiviral activity, suggesting that the carbohydrate moiety played a critical role in the inactivation of EMCV. This research provides a green strategy for the production of huge amounts of antiviral substances from a sustainable bio-resource.