A kinetic model for evaluation of the antioxidant activity of several rosemary extracts

The antioxidant properties of phenolic diterpenes in several rosemary (Rosmarinus officinalis) extract formulations were investigated. Carnosic acid, carnosol and methyl carnosate were identified and quantified by high-performance liquid chromatography (HPLC) and carnosic acid was found to be the most abundant phenolic compound in the rosemary extracts investigated. To describe the antioxidant properties the free radical scavenging activity using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) test and the antioxidant activity coefficient in the β-carotene–linoleic acid emulsion system, CAA, were assayed. In both assays, extracts with higher total phenolic contents were superior in antioxidant activity. To interpret the antioxidant properties the kinetic approach was used. A power function was found to best represent the time dependence of the content of free radicals scavenged, as well as the content of β-carotene bleached in the presence of rosemary extracts. The rate of free radical scavenging, RS, and the rate of β-carotene bleaching, RB, were estimated and suggested as new parameters to describe the antioxidant activity of rosemary extracts. The kinetic data were interpreted in terms of differences in the reactivity of antioxidant compounds.