Characterisation of the antioxidant properties of de-odourised aqueous extracts from selected Lamiaceae herbs

De-odourised aqueous extracts of four commonly consumed herbs belonging to the Lamiaceae family, i.e. oregano (Origanum vulgaris L.), rosemary (Rosmarinus officinalis L.), sage (Salvia officinalis L.) and thyme (Thymus vulgaris L.), were investigated for their antioxidant properties. Various experimental models were used for the characterisation of the activity, including iron reduction capacity, DPPH, ABTS+ and OH radical-scavenging activities and the capacity of the extracts to inhibit copper-induced oxidation of human low-density lipoproteins (LDL) ex vivo. The extracts showed varying degrees of reductive and radical scavenging capacity, and were capable of a marked prolongation of the lag-time in the LDL oxidation assay. The hierarchy of the observed antioxidant activity of the extracts was dependent on the type of assay used. The observed antioxidant characteristics were not fully related to the total phenolic contents of the extracts in any of the assays, but were presumably strongly dependent on rosmarinic acid, the major phenolic component present in this type of Lamiaceae extract.