SPME determination of volatile aldehydes for evaluation of in-vitro antioxidant activity.

The in-vitro antioxidant activity of natural (essential oils, vitamin E) or synthetic substances ( tert-butyl hydroxy anisole (BHA), Trolox) has been evaluated by monitoring volatile carbonyl compounds released in model lipid systems subjected to peroxidation. The procedure employed methodology previously developed for the determination of carbonyl compounds as their pentafluorophenylhydrazine derivatives which were quantified, with high sensitivity, by means of capillary gas chromatography with electron-capture detection. Linoleic acid and sunflower oil were used as model lipid systems. Lipid peroxidation was induced in linoleic acid by the Fe2+ ion (1 mmol L-1, 37 degrees C, 12 h) and in sunflower oil by heating in the presence of O2 (220 degrees C, 2 h). The change in hexanal (the main lipoxidation product) concentration found in the lipid matrix subjected to oxidation with and without the substance being tested was used to calculate the antioxidant protection effect. These procedures were employed to evaluate the antioxidant activity of the essential oils of cilantro ( Coriander sativum L.), fennel ( Foeniculum vulgare Mill.), rosemary ( Rosmarinus officinalis L.), "salvia negra" ( Lepechinia schiedeana), and oregano ( Origanum vulgare L.), and the well-known antioxidants BHA, vitamin E, and Trolox, its water-soluble analog. In the sunflower oil system, the essential oils had a stronger protective effect against lipid peroxidation than BHA, vitamin E, and Trolox within the range of concentrations examined (1-20 g L-1). The highest protecting effect, corresponding to a 90% drop in hexanal release, was observed for cilantro oil at 10 g L-1.