Abstract
Determination of total α, β-unsaturated. aldehydes (USA) in autoxidized lipids was attempted by means of a 2, 4-diaminotoluene (DAT) fluorescence method as a new evaluation method for lipid oxidation. α, β-USA were reacted with 2, 4-DAT in an acidic medium, and the fluorescence of the products, 7-amino-6-methylquinoline derivatives, was measured (excitation at 394nm and emission at 494nm). In the time-course of lipid autoxidation, the total α, β-USA value in lipids was compared with the peroxide value (POV) and the thiobarbituric acid value (TBAV). Total α, β-USA amounts were correlated with TBAV in four edible oils (olive, peanut, rapeseed, and sesame oils) within 20 hours during autoxidation at 80°C under aeration (100ml/min), but only total α, β-USA was still increasing after more than 50 hours of autoxidation. In fatty acid methyl esters, about 1, 000μg/g (as acrolein) of total α, β-USA was detected in 20 hour-autoxidized methyl linolenate, whereas the TBAV value was 500μg/g as malondialdehyde. It is of interest that 20 hour-autoxidized methyl oleate, which possesses only one double bond, contained about 500μg/g of total α, β-USA, whereas the TBAV level was only 40μg/g. Therefore, we consider that the determination of total α, β-USA was suitable for the evaluation of lipid alteration. Finally, 7-amino-6-methylquinoline derivatives of a, α, β-USA (C3-C10) were separated in preliminary high-performance liquid chromatographic studies and acrolein, crotonaldehyde, 2-pentenal, 2-heptenal and 2-nonenal were detected in the 20-hour-autoxidized methyl linoleate.
