Identification of volatile components in basil (Ocimum basilicum L.) and thyme leaves (Thymus vulgaris L.) and their antioxidant properties

Aroma compounds in the extracts of basil leaves (Ocimum basilicum L.) and thyme leaves (Thymus vulgaris L.) were identified by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The major aroma constituents of basil were 3,7-dimethyl-1,6-octadien-3-ol (linalool; 3.94 mg/g), 1-methoxy-4-(2-propenyl) benzene (estragole; 2.03 mg/g), methyl cinnamate (1.28 mg/g), 4-allyl-2-methoxyphenol (eugenol; 0.896 mg/g), and 1,8-cineole (0.288 mg/g). The major aroma constituents of thyme were 2-isopropyl-5-methylphenol (thymol; 8.55 mg/g), 4-isopropyl-2-methylphenol (carvacrol; 0.681 mg/g), linalool (0.471 mg/g), α-terpineol (0.291 mg/g), and 1,8-cineole (0.245 mg/g). Twelve aroma constituents of basil and thyme were examined for their antioxidant activities using the aldehyde/carboxylic acid assay. Eugenol, thymol, carvacrol, and 4-allylphenol showed stronger antioxidant activities than did the other components tested in the assay. They all inhibited the oxidation of hexanal by almost 100% for a period of 30 days at a concentration of 5 μg/ml. Their antioxidant activities were comparable to those of the known antioxidants, α-tocopherol and butylated hydroxy toluene (BHT).