Antioxidant Properties of O. Onites, T. Vulgaris and O. Basilicum Species Grown in Greece and Their Total Phenol and Rosmarinic Acid Content

This study determined the total phenol (TP), rosmarinic acid (RA) content and the free‐radical scavenging and ferric‐reducing antioxidant properties of acetonic and methanolic extracts of O. onites (oregano), T. vulgaris (thyme) and O. basilicum (basil) species (Crete, Greece). Oregano and thyme were higher in their 2,2′‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity than basil (EC50: 0.489, 0.555, 1.16 mg/mL, respectively). In ferric reducing antioxidant power (FRAP) assay oregano was superior to thyme and basil (EC50: 0.04, 0.088 and 0.1452 mg/mL, respectively), as high as butylated hydroxytoluene (BHT) (EC50: 0.0365 mg/mL). RA was a stronger radical scavenger than BHT and α‐tocopherol (EC50: 0.032, 0.083 and 0.123 mg/mL, respectively) and as strong a reducing agent as ascorbic acid (EC50: 0.00216, 0.0033 mg/mL). Thyme was the richest source of RA compared to oregano and basil (4,532, 3,280 and 2,372 mg/kg dry leaf, respectively). Oregano and thyme are more potent antioxidant sources than basil. The high positive correlations between TP, RA and DPPH activity (r = 0.854, r = 0.924, P < 0.05), indicate the significant contribution of o‐dihydroxyphenolic compounds to the antioxidant activity of the plant extracts. PRACTICAL APPLICATONS The studies reported may prove beneficial in the exploitation of natural antioxidant sources for the preservation and/or extension of the shelf life of raw and processed foods.