Antioxidant activity of aqueous tea infusions prepared from oregano, thyme and wild thyme

Using a multiple-method approach, antioxidant activity of aqueous tea infusions prepared from oregano (Origanum vulgare L. ssp. hirtum), thyme (Thymus vulgaris L.) and wild thyme (Thymus serpyllum L.) were tested in relation to their chemical composition. Total phenolic, flavonoid, catechin and anthocyanin content was determined by spectrophotometric methods. Oregano aqueous tea infusion had the highest amount of total phenols (12 500 mg/L gallic acid equivalent, GAE) and flavonoids (9000 mg/L GAE). Identification of polyphenolic compounds in aqueous tea infusions by HPLC-PDA analysis showed a dominant presence of rosmarinic acid (in mg/g): 123.11 in oregano, 17.45 in thyme and 93.13 in wild thyme. Antioxidant activity of aqueous tea infusions was evaluated using four antioxidative methods (the β-carotene bleaching method (BCB), the 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method, the thiobarbituric acid reactive species (TEARS assay) and the induction period of lard oxidation (Rancimat assay)). The results were compared with natural (ascorbic acid and α-tocopherol) and synthetic antioxidants, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). Oregano aqueous tea infusion showed the strongest antioxidant activity using three methods (the β-carotene bleaching method, DPPH radical scavening method and Rancimat assay), while thyme and wild thyme showed weaker and relatively similar antioxidant activity.