Viljem Vek

Extractives of mechanically wounded wood and knots in beech

Abstract Various types of wound-associated wood, such as discoloured wood including knots of living and dead branches, were sampled from common beech trees (Fagus sylvatica L.), extracted, and the extracts have been analysed by GC and colourimetry assay. Sequential pressurised solvent extraction was applied with cyclohexane and aqueous methanol. The yield of hydrophilic compounds was three to five times higher than that of lipophilic extractives. The fractions differed mainly in their hydrophilic moieties. The lipophilic extractives consisted mainly of free fatty acids, fatty alcohols and free sterols. The yield of fatty acids was slightly higher in reaction zones and knots. The content of free sterols was highest in the reaction zones and in the discoloured wood. The hydrophilic extractives consisted of soluble sugars, various acids and phenolic compounds with catechin as the dominant one. Expectedly, the yield of phenolic extractives and catechin (proanthocyanidins) was highest in knots and wound-wood. Discoloured wood gave rise to lower amounts of catechin.

Comparison of two extraction and two chromatographic methods in analysis of beech wood extractives

Parallel samples of beech wood were extracted in a Soxhlet apparatus and in a system for accelerated extraction, and further evaluated with gas chromatography (GC) and high performance liquid chromatography (HPLC). A strong correlation between the content of hydrophilic extractives obtained by the two extraction methods was found. In addition, a strong correlation between the content of catechin quantified with GC after speed extraction and with HPLC after Soxhlet extraction was revealed. These relationships have practical use in quick assessment of the chemical properties of beech wood.