Optimization of extraction of antioxidants from aromatic herbs and their synergistic effects in a lipid model system

Response surface methodology was applied to improve the polyphenol extraction process of rosemary, oregano, sage, and thyme. Aqueous ethanol (EtOH 50%) rendered the highest polyphenol extraction yield for all tested samples. Based on their total phenolic contents, rosemary, oregano, and thyme were selected for evaluation of their scavenging activities towards DPPH radical and ABTS radical cation and application in an oil model system. All extracts decreased the production of primary oxidation compounds during Schaal oven test storage. The induction period, as evaluated by the Rancimat test, was also reduced. There was an agreement between both oil model system assays, and rosemary extract showed the highest antioxidant capacity, followed by thyme and oregano. A centroid simplex design was used to evaluate the synergistic effect among the samples. Rosemary was able to play a synergistic effect when combined with thyme and oregano, or when used in binary mixtures.