& Key message Total bark extractive content increases at positions higher in the trunk of Abies alba Mill. trees. The greatest proportions of bark polyphenolic extractives are found in the lower section of the trunk, below the crown. & Context The bark of commercially grown softwood trees is a potentially valuable source of secondary metabolites including polyphenols such as tannins, used in the manufacture of adhesives and resins. There is little information about how the yield and composition of bark extracts vary longitudinally within trees and with respect to the presence or absence of branches. & Aims We examined the variability of bark secondary metabolites in the softwood Abies alba both longitudinally within trees and among trees at specific sample heights. The aim was to determine whether specific bark fractions within this species contain more extractable secondary metabolites than others. & Methods Eight trees of A. alba were harvested, and up to 13 discs were cut along the trunk from 30 cm above the ground to where the trunk was only 10 cm in diameter. Milled bark was extracted with water:ethanol (1:1) using an accelerated solvent extractor and the dry yield calculated. Extract composition was examined by liquid chromatography followed by mass spectrometry. & Results Total extract yield increased from the base of the tree towards the top. The yield of the most abundant polyphenolic compounds decreased from the base of the tree towards the top, indicating the total extracts included compounds that were not detectable with the chromatographic method used.
Knotwood of softwood species is rich in secondary metabolites, especially lignans. These metabolites can be extracted with organic solvents, and are known to be valuable sources of natural bioactive molecules. Here, we examine the intraspecific variability of the yield and compositions of ethanol extracts from knotwood along the stems of three economically significant softwoods Abies alba, Picea abies and Pseudotsuga menziesii in view of further valorisation. Extractive yields from all three species were higher from knots at the base of the living crown than at the top. Lignans and terpenes were abundant in A. alba and P. abies extracts, and lignans were present in the highest concentrations at the crown base. Secoisolariciresinol and hydroxymatairesinol were the most abundant lignans in A. alba and P. abies, respectively. P. menziesii extract composition was more diverse than those of the other species, containing taxifolin, small amounts of the lignan nortrachelogenin, and smaller amounts of secoisolariciresinol. A cyclitol, D-pinitol, was found in high concentrations in extracts from knots at the very top of the crown, particularly in A. alba and P. menziesii. Lignans, taxifolin and D-pinitol are reported to have anti-tumour properties, and valuable food-supplement markets exist for these compounds suggesting possibilities of further valorisation.
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