Amounts of the reactive aldehydes, malonaldehyde, 4-hydroxy-2-hexenal, and 4-hydroxy-2-nonenal in fresh and oxidized edible oils do not necessary reflect their peroxide and anisidine values

Abstract

There is a growing development of foods and food supplements enriched in n-3 lipids, whereas quantitative data on oxidation products present throughout the food chain are lacking. To give a first insight of the range of potentially toxic aldehydes that can be encountered in these foods, malondialdehyde (MDA), 4-hydroxy-2-hexenal (4-HHE) and 4-hydroxy-2-nonenal (4-HNE) were quantified in a set of four fresh and oxidized oils presenting large variations in unsaturation levels, n-6/n-3 ratio and oxidabilities. Results were compared to classical methods. In fresh rapeseed, sunflower, kiwiseed, and tuna oils, the concentrations of MDA ranged between 0.6 and 29μmolkg-1 oil, of hydroxyalkenals between 0.1 and 3.3μmolkg-1, hydroperoxides concentrations (HPX) ranged between 0.4 and 4mmolkg-1 oil, peroxide value (PV) and anisidine value (AV) were well below the acceptable limits. In oxidized rapeseed, kiwiseed, and tuna oils 4-HHE ranged from 120 to 150μmolkg-1, whereas MDA ranged from 600 to above 1100μmolkg-1. Conversely, sunflower oil exhibited the highest quantities 4-HNE (175μmolkg-1) but the lowest of MDA (100μmolkg-1) and 4-HHE (2.9μmolkg-1) in agreement with its fatty chain composition. Altogether, the results highlight the interest of using methods able to quantify specific oxidation products and not only PV and AV to assess lipid oxidation especially in oils or products containing high quantities of n-3 FA. Practical applications: This work provides quantitative data regarding amounts of toxic aldehydes that can be present in edible oils. The used methods made it possible to quantify MDA, 4-HNE, and 4-HHE as respective markers of oxidation of polyunsaturated fatty acids in a whole, n-6 and n-3 polyunsaturated fatty acids. They could be applied to oils, fats, and food products to better estimate the occurrence and exposure to these compounds. Comparison with methods currently used to evaluate the quality of edible oils indicates clearly that the dynamics of formation of the different oxidation markers are oil-specific. Thus, oxidation indicators should be selected as regard to fatty chain profiles and not used to compare oils with very different profiles of polyunsaturated fatty acids.These tools could be used to design nutritional, metabolic, and toxicological trials avoiding too unrealistic exposures in undesirable contaminants.