Post-Harvest Chemical Staining in Blackwood (Acacia melanoxylon R. Br.)

Summary

This is the first report of post-harvest wood staining in blackwood (Acacia melanoxylon R. Br). In Tasmanian sawmills, an orange-brown stain commonly occurs upon cutting fresh blackwood. An investigation of the causal mechanism of stain development was completed using fresh flitches and stockpiled logs. Some fungi and bacteria were isolated from stained and unstained blackwood, but no species was consistently present in stained wood alone. Wood pH did not vary between stained and unstained wood, but there was some evidence of alterations in phenol composition. Blackwood extracts were analysed by HPLC and a minor phenolic compound was detected that was consistently found in stained samples and rarely in unstained. UV spectra indicated that this compound may be a quinone, but mass spectrometry data was inconclusive. Experiments with blackwood extracts showed that addition of oxygen (by means of H₂O₂ treatment) increased absorbance in the “brown” wavelengths characteristic of stain. This supports the assumption that the stain is an oxidative chemical stain, as it develops quite rapidly from cut surfaces.