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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.

The aim of the study was to examine the amounts of extractives in sapwood and heartwood of black locust recovered using three different conventional extraction techniques and three different solvent compositions. Heartwood contained larger amounts of total phenols, dihydrorobinetin and robinetin than sapwood, irrespective of the extraction technique and solvent used. Dihydrorobinetin and robinetin were the characteristic phenolic compounds of black locust wood, whereas the concentration of dihydrorobinetin was significantly higher. The highest concentrations of examined extractives were obtained by Soxhlet extraction. More than ninety percent of extractives were leached from wood in a Soxhlet apparatus in less than 2 hours. Maceration with stirring and ultrasonic extraction gave smaller yields of extractives. The amounts of total extractives, total phenols and robinetin leached with the three solvents were comparable. Extraction of heartwood with acetone yielded significantly larger amounts of dihydrorobinetin than extraction with methanol or ethanol. Four hours extraction of wood meal with aqueous acetone in a Soxhlet apparatus was found to be the optimal extraction procedure for the recovery of dihydrorobinetin.