RECENT ADVANCES IN LIPID OXIDATION

In a major pathway of the autoxidation of methyl linolenate, peroxyl radicals of the internal hydroperoxides undergo rapid 1,3-cyclisation to form hydroperoxyepidioxides. Because linolenate hydroperoxides are relatively unstable, free radical antioxidants are much less effective in linolenate oils than in linoleate oils. Tocopherols and carotenoids effectively inhibit photosensitised oxidation of vegetable oils. Direct gas chromatographic analyses of malonaldehyde do not correlate with the TBA test. Model fluorescence studies indicate that malonaldehyde may not be so important in crosslinking with DNA. In contrast to oxidised methyl linoleate, oxidised trilinolein does not form dimers. Although trilinolein oxidises with no preference between the 1(3)- and 2-triglyceride positions, the n-3 double bond of trilinolenin oxidises more in the 1(3)- than in the 2-position. Synthetic triglycerides oxidise in the following decreasing relative rates: LnLnL, LnLLn, LLnL, LLLn (Ln = linolenic and L = linoleic). To estimate the flavour impact of volatile oxidation products their relative threshold values must be considered together with their relative concentration in a given fat.