The aroma extracts were identi¼ed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The major aroma compounds of the plant extracts were sulphides, alcohols and heterocyclic compounds. Antioxidant activities of the aroma extracts were evaluated using two different assays. The aroma extracts isolated from green pepper, Welsh onion, onion and garlic inhibited the oxidation of hexanal by 51%, 95%, 96% and 98%, respectively, for 1 month at a level of 500 mg/ml; these extracts inhibited malonaldehyde formation from cod liver oil by 49%, 58%, 62% and 58%, respectively, at a level of 500 mg/ml. Their antioxidant activities were comparable to that of the natural antioxidant a-tocopherol.