Antioxidant activity of rosemary and thyme by-products and synergism with added antioxidant in a liposome system

This study describes the use of liposomes as biological membrane models to evaluate the potential of natural antioxidants as inhibitors of lipid peroxidation. Antioxidative effects of by-products from manufacturing of essential oils, i.e., distilled rosemary leaf residues (DRL), distilled thyme leaf residues (DTL), and the combined antioxidative effects of DRL or DTL with alpha-tocopherol (TOH), ascorbic acid (AA), and quercetin (QC) on peroxidation of l-alpha-phosphatidylcholine liposomes as initiated by hydrophilic azo-initiators, were investigated. In addition, experiments were repeated with whole thyme leaves (TL) to compare the characteristics of by-products (leaf residues from distillation) with the initial industrial product (leaf for distillation). Extracts from DRL, DTL, and TL all had an obvious antioxidative effect as evidenced by a lag phase for the formation of phosphatidylcholine-derived conjugated dienes. DRL and DTL had similar antioxidative activity, while whole thyme leaves showed superior antioxidant activity compared with distilled thyme residues. Combination of TOH or QC with DRL, DTL, and TL, respectively, showed synergism in prolonging of the lag phase.