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 alpha-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.