Variations in Resin Content and Composition

The biosynthesis of extractives is controlled genetically and hence each wood species tends to produce specific substances. As a result of secondary changes, heartwood contains a large variety of phenolic substances. From the chemotaxonomical point of view, chemical structures of various flavonoids, lignans, stilbenes, and tropolones are of interest. For example, species within genera such as Pinus, Acacia, and Eucalyptus can be classified according to their characteristic composition of phenolic substances. 

The resin content of wood and its composition vary considerably, depending on such factors as place of growth, age of the tree, and genetic factors. For example, the resin content of Norway spruce (P/cea abies) is considerably higher for stems grown in the northern than in the southern parts of Scandinavia. The resin content within the same stem also varies, but in a very irregular manner. In all pines, the heartwood contains much more resin than the sapwood, whereas the opposite seems to be true for P/cea species as indicated by data for Norway spruce. The heartwood extractives in both pine and spruce contain resin acids and free fatty acids as main components, 

After felling of a tree the content of extractives decreases, and their composition changes because of various reactions. For acid sulfite pulping, the changes are beneficial, and wood is usually stored for several months to minimize pitch problems and to lower the resin content of the pulp. In the case of kraft pulping, storage of wood has detrimental consequences, since yields of both turpentine and tall oil are reduced. 

The resin reactions involve both oxidation by air and enzymic hydrolysis. These processes proceed simultaneously, and fats and waxes are mainly hydrolyzed enzymically. Because of both hydrolysis and oxidation the hy-drophilicity of the resin constituents is increased. These reactions are largely influenced by the conditions during storage. For example, logs are better preserved when submerged in water than when stored on land. The resin 

Assarsson, A. (1969). Changes in resin during wood storage. Sven. Papperstidn. 72, 304-311. (In Swed.) 

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