Assessment of Ferric-Reducing/Antioxidant Power in the Foliage of Several Tree Species

Recently considerable attention has been given to the presence of non-enzymatic antioxidant compounds present in plant foliage. Carotenoids (xanthophylls + carotenes) have been identified as a class of compounds that have antioxidant abilities. New evidence suggests that phenylpropanoids (hydroxycinnamic acids + flavonoids) may also play a role in oxygen freeradical scavenging. The Ferric-Reducing/Antioxidant Power (FRAP) assay was used to examine these oxygen-reducing compounds in the foliage of ten tree species. The FRAP assay is a rapid and direct test that has been used primarily to quantify the capability of non-enzymatic antioxidants in animal systems and has rarely been used for plants. Foliage from five coniferous (Juniperus virginiana, Pinus sylvestris, Picea pungens, Thuja occidentalis and Ginko biloba) and five deciduous (Rhamnus catharticus, Acer saccharum, Fraxinus pennsylvanica, Robinia pseudoacacia and Quercus rubra) species was examined. Soluble carotenoids and phenylpropanoids were extracted from foliage in a methanol solution. Concentrations of these compounds were measured spectrophotometrically and FRAP assays performed on these extracts. There was a significant positive correlation (P\u3c0.05) observed between concentrations of soluble phenylpropanoids (assessed at 300 nm) and FRAP values in T. occidentalis, A. saccharum and F pennsylvanica. In addition there was a weak, but significant (P\u3c0.10), positive relationship observed between these two variables across all species and was strongest for the deciduous lifeform (P\u3c0.05). These results suggest that phenylpropanoid concentrations may play an important role in the scavenging of oxygen free-radicals in the foliage of some tree species