Abstract
The chemical composition of maritime pine ( Pinus pinaster) bark and of alkaline bark extracts has been investigated with bark from trees grown in Portugal. Bark is composed of lignin and polyphenolics (ca. 44%), polysaccharides (ca. 39%), dichoromethane, ethanol and water extractives (ca. 17%) and ashes (ca. 1%). The lignin content determined by the Klason method, after the extraction of polyphenolics (tannin-rich fraction) from the bark by alkali solution, is 33.2%. Cellulose content is about 24%. Hemicelluloses (about 15% of bark dry weight) are suggested to be predominantly composed of arabinoglucuronoxylans and minor amounts of galactoglucomanans. The bark lignin is composed by p-hydrophenylpropane and guaiacylpropane units in proportions of 20:80. The condensed tannins are constituted mainly by catechin-type structural units. The direct extraction of bark with aqueous alkaline solutions yields extracts which contain sugars, lignin and condensed tannins. The number average molecular weights ( M n) of alkaline extracts are in the range 1000–1500. The composition and M n of extracted substances depends on the alkaline extraction conditions.
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