Radial distribution and partial characterization of lipids in the trunk of three hardwoods

The lipids extracted from wood zones of different age across the trunk cross sections of three hardwood species differing in their ability to form heartwood (Tilia cordata Mill., Betula verrucosa Ehrh., and Robinia pseudoacacia L.) were partly characterized. In all trees, the lipid concentration rises towards the interior of the trunk. The lipid from Robinia shows, compared to that ofTilia and Betula, high acid values. Lipid extracted from the innermost sapwood of Robinia exhibits maximum acidity. In Robinia and Tilia the innermost parts of the trunk show minor acid values. Lipid of Betula, however, shows no acidity radial gradient. The ester value, the iodine value and the mount of unsaponifiable material are highest in the lipids extracted from the innermost heartwood of Robinia. These lipid characteristics are more or less constant across the trunk of Tilia. Betula trunk indicates a slight increase of the ester value and the proportion of unsaponifiable material towards the pith. The increase in lipid concentration in the Robinia trunk is not due to an accumulation of triglycerides and phospholipids, but to polar compounds which seem to originate at the sapwood-heartwood boundary. The fatty acid pattern of the saponifiable lipid fraction shows no change towards the centre in the trunk of Tilia and Betula. This fraction in the heartwood of Robinia, however, exhibits higher amounts of linoleic acid, eicosenoic acid and behenic acid, while the saponifiable lipid from the sapwood contains higher concentrations of shorter chain fatty acids (C₁₂— C₁₆).