Abstract

The influence of tree height on the composition of bark extractives from Eucalyptus globulus and Eucalyptus nitens was investigated for its potential in the sourcing of valuable compounds. The bark of these trees was extracted at different heights to obtain lipophilic and hydrophilic compounds, which were chemically characterized. The extraction yield of lipophilic compounds was higher for E. globulus than for E. nitens. The type and proportion of the compounds changed with the tree variety and height. The main compounds detected were triterpenic acid derivatives, such as lupane, oleanane and ursane types, followed by fatty acids. The yield extraction of the hydrophilic compounds was higher for E. nitens than E. globulus. The total phenolic content, proanthocyanidins and antioxidant activity of the extracts increased with the tree height in both cases. However, the E. globulus extracts [half maximal inhibitory concentration (IC50)=13.8 +/- 0.2 mu g ml(-1) showed higher antioxidant activity than did the E. nitens extracts (IC50 = 22.8 +/- 0.2 mu g ml(-1)). Differences in the extract composition and the spatial conformation of the molecules (steric effect) could also help to obtain a higher antioxidant capacity from E. globulus extracts. These results show that differentiation by tree height can contribute to the selective enrichment of these valuable compounds.