Abstract
The chemical composition of extractives in the sapwood (SW), heartwood (HW), knotwood (KW), and branchwood (BW of silver fir (Abies alba Mill.) was analyzed, and their antifungal and antioxidant properties were studied. In addition, the variability of extractives content in a centripetal direction, i.e., from the periphery of the stem towards the pith, was investigated. The extracts were analyzed chemically with gravimetry, spectrophotometry, and chromatography. The antifungal and antioxidative properties of the extracts were evaluated by the agar well diffusion method and the diphenyl picrylhydrazyl radical scavenging method. Average amounts of hydrophilic extractives were higher in KW (up to 210.4 mg/g) and BW (148.6 mg/g) than in HW (34.1 mg/g) and SW (14.8 mg/g). Extractives identified included lignans (isolariciresinol, lariciresinol, secoisolariciresinol, pinoresinol, matairesinol) phenolic acids (homovanillic acid, coumaric acid, ferulic acid), and flavonoids epicatechin, taxifolin, quercetin). Secoisolariciresinol was confirmed to be the predominant compound in the KW (29.8 mg/g) and BW (37.6 mg/g) extracts. The largest amount of phenolic compounds was extracted from parts of knots (281.7 mg/g) embedded in the sapwood and from parts of branches (258.9 mg/g) adjacent to the stem. HW contained more lignans in its older sections. Hydrophilic extracts from knots and branches inhibited the growth of wood-decaying fungi and molds. KW and BW extracts were better free radical scavengers than HW extracts. The results of the biological activity tests suggest that the protective function of phenolic extracts in silver fir wood can also be explained by their antioxidative properties. The results of this study describe BW as a potential source of phenolic extractives in silver fir.
Highlights
Woody biomass has attracted much scientific attention in which it is treated as a potential source of bioactive phytochemicals, known as extractives [1,2,3]
Willför et al [1,2,6] comprehensively investigated the contents of hydrophilic extractives and individual lignans that can be extracted from knotwood (KW) and stemwood (SW) of various conifer species
The SW with the lowest phenolic content had an average of only 1.3 milligrams of total phenols (TP) per gram of dry wood; larger amounts were measured in HW samples
Summary
Woody biomass has attracted much scientific attention in which it is treated as a potential source of bioactive phytochemicals, known as extractives [1,2,3] These natural compounds are not distributed in tree tissues. Knots of silver fir contained significantly higher amounts of hydrophilic extractives than SW or HW. The lignan secoisolariciresinol was the dominant compound in KW extracts, while matairesinol was characteristic of the HE samples. [8] reported that aqueous extract from the wood of silver fir branches contains lignans, which constitute about 10% of the extract and include isolariciresinol, hydroxymatairesinol, secoisolariciresinol, lariciresinol, pinoresinol, and matairesinol. The amount of lipophilic extractives is reported to be lower than the amount of hydrophilic extractives in coniferous knots [9]. As reported by Kebbi-Benkeder et al [7], the hexane extracts of silver fir KW contained mainly terpenes, i.e., dehydrojuvabione and juvabione; these two were referred to as dominant compounds, together with epimanool, tumerone, farnesol, eudesmol, nerolidol, and isopimaric acid
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