Determination of Antioxidant Charge and Total Phenolic Content in Greek aromatic plants by EPR/UV-Vis Spectroscopy

Aromatic plants and herbs are among the more important sources of phenolic compounds, which have been reported to show strong antioxidant activity. In the present work the total phenolic content and the antioxidant charge of five aromatic plants, Origanum vulgare L., Rosmarinus officinalis L., Ocimum basilicum L., Salvia officinalis L. and Achillea millefolium L., biologically grown in Western Greece, was determined by UV-vis and Electron Paramagnetic Resonance (EPR) spectroscopy. Dried plant leaves extracted in 50% methanol/ 48,5% H2O/ 1,5% formic acid solution were measured by UV-vis spectroscopy for the determination of total phenolics. Quantitative analysis has been done by using Gallic acid as standard solution. In addition the dry matter of plant leaves was measured at 77Kelvin by EPR spectroscopy. The EPR spectra of all samples contained stable radical signal with g-values 2.0046-49 and a linewidth of 3-5Gauss. These are characteristic of phenolic or quinone-type radicals with the unpaired electron partially on the Oxygen atom of the phenolic ring. Quantitative analysis of the radicals has been done using DPPH [1mm3 2x1013 spins] as reference. The calculations have been done per dry mass of the material. The present results reveal significant differences of radical concentration between samples of different origin by EPR spectra. The higher radical content was measured in Origanum vulgare L. and the lower in Ocimum basilicum L. plant leaves respectively. In addition a significant difference in total phenolics content was determined between plants. The higher concentration was found in Origanum vulgare L. and the lower in Achillea millefolium L. plant leaves respectively. It is concluded that a fraction of the total phenolics accumulation corresponds to the redox active antioxidant charge in plant leaves.