Topochemical investigations of wood extractives and their influence on colour changes in American black cherry (Prunus serotina Borkh.)

The topochemical distribution of accessory compounds responsible for wood colouration during heartwood formation and processing of black cherry (Prunus serotina) is restricted to the axial and ray parenchyma cells. (+)-Catechin, taxifolin, aromadendrin, eriodictyol, naringenin, 4′-methoxynaringenin and prunin were identified in acetone/water extracts. However, the colour of wood after extraction is still reddish-brown, indicating that the coloured material is polymeric (cross-linked, condensed). It was demonstrated that (+)-catechin plays a pivotal role in the development of heartwood colour. Its concentration at the sapwood/heartwood boundary decreases, presumably due to the formation of non-soluble polymeric proanthocyanidins. Heat treatment of heartwood during veneer production intensifies the reddish-brown heartwood colour, probably by promoting the polymerisation of (+)-catechin and other flavonoid monomers.