Variability in content of hydrophilic extractives and individual phenolic compounds in black locust stem

The main goal of this study was to investigate the amounts of hydrophilic extractives in bark and wood samples of black locust stem (Robinia pseudoacacia L.). Six adult trees were included in the present investigation. Samples were taken from each felled trunk at four different heights. Material was extracted with a mixture of acetone and water, and the hydrophilic extractives were, then, qualitatively and quantitatively analysed. The highest contents of hydrophilic extractives, total phenols, dihydrorobinetin and robinetin were measured in wound-wood and heartwood. The concentrations of extractives were highest in the outermost samples of heartwood. Knotwood of black locust contained less dihydrorobinetin than heartwood. Significantly less hydrophilic compounds were extracted from bark and sapwood samples. This study shows that heartwood of black locust can be considered a source of value-adding compounds. The investigation showed significant variability in the content of extractives in radial direction and less pronounced axial variability within the black locust stems.