Antioxidant activity and characterization of volatile extracts of Capsicum annuum L. and Allium spp.

Plants that are commonly used in kimchi, a traditional Korean fermented food, include Capsicum annuum L. (green pepper), Allium fistulosum L. (Welsh onion), Allium cepa L. (onion) and Allium scorodoprasm L. (garlic), each of which has its own aroma. Aroma extracts of the plants were isolated by steam distillation under reduced pressure (DRP) and liquid–liquid continuous extraction (LLE). The aroma extracts were identified 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 µg/ml; these extracts inhibited malonaldehyde formation from cod liver oil by 49%, 58%, 62% and 58%, respectively, at a level of 500 µg/ml. Their antioxidant activities were comparable to that of the natural antioxidant α‐tocopherol.