Wood photostabilization roles of the condensed tannins and flavonoids from the EtOAc fraction in the heartwood extract of Acacia confusa

Lignin, one of the three major components in wood, can absorb UV light and react with ¹O₂, leading to wood photodegradation. Previous studies demonstrated the ethyl acetate (EtOAc) fraction of the heartwood extract in Acacia confusa (AcHW) has good photostabilities to prevent photodegradation of the wood. However, these effective constituents have different structural characteristics and may affect their photostabilities and protection efficacies on wood which need to be clarified. This study analyzed the polyphenolic contents, chemical constituents and photostabilities of the six subfractions (EA1–EA6) which successively fractioned from the EtOAc fraction in AcHW by the colorimetric methods, UV/Vis spectrophotometry and high-performance liquid chromatography and evaluated the wood photoprotection abilities of these treatments. The results showed the more flavones and flavonols contained in the subfractions, the better the UVA absorptivity was. Besides, the catecholic-condensed tannins and flavonoids in these subfractions also provide good ¹O₂ quenching abilities and phenoxyl radical scavenging abilities. Advanced results also established in these subfractions, melanoxetin, transilitin, 7,3′,4′-trihydroxy-3-methoxyflavone, 7,8,3′-trihydroxy-3,4′-dimethoxyflavone (flavonols), 7,8,3′,4′-tetrahydroxyflavone, 7,3′,4′-trihydroxyflavone, 7,3′,4′-trihydroxy-5-methoxyflavone (flavones) and okanin (chalcone) can absorb the energy of UVA light; the condensed tannins, 3,4-dihydroxybenzoic acid (phenolic acid), melacacidin-based oligomers, melacacidin, 4-O-methylmelacacidin, 4′-O-methylmelacacidin (melacacidin-based flavanols), 3,7,8,3′,4′-pentahydroxyflavanone (flavanonol), 7,8,3′,4′-tetrahydroxyflavanone (flavanone), the flavones, flavonols and chalcone can suppress the phenoxyl radicals; the condensed tannins, melacacidin-based oligomers and the flavonoids can quench ¹O₂. Hence, the photostability of extract-free wood slices treated with these effective constituents was consequently enhanced. In summary, these results clearly demonstrated the multiple wood photoprotection actions of these effective constituents and their potential as natural wood photostabilizers.