Contribution of lipid oxidation products to acrylamide formation in model systems

The reactions of asparagine with methyl linoleate (1), methyl 13-hydroperoxyoctadeca-9,11-dienoate (2), methyl 13-hydroxyoctadeca-9,11-dienoate (3), methyl 13-oxooctadeca-9,11-dienoate (4), methyl 9,10-epoxy-13-hydroxy-11-octadecenoate (5), methyl 9,10-epoxy-13-oxo-11-octadecenoate (6), 2,4-decadienal (7), 2-octenal (8), 4,5-epoxy-2-decenal (9), and benzaldehyde (10) were studied to determine the potential contribution of lipid derivatives to acrylamide formation in heated foodstuffs. Reaction mixtures were heated in sealed tubes for 10 min at 180 degrees C under nitrogen. The reactivity of the assayed compounds was 7 >> 9 > 4 > 2 >> 8 - 6 >> 10 similar to 5. The presence of compounds 1 and 3 did not result in the formation of acrylamide. These results suggested that alpha,beta,gamma,delta-diunsaturated carbonyl compounds were the most reactive compounds for this reaction followed by lipid hydroperoxides, more likely as a consequence of the thermal decomposition of these last compounds to produce alpha,beta,gamma,delta-diunsaturated carbonyl compounds. However, in the presence of glucose this reactivity changed, and compound 1/glucose mixtures showed a positive synergism (synergism factor = 1.6), which was observed neither in methyl stearate/glucose mixtures nor in the presence of antioxidants. This synergism is proposed to be a consequence of the formation of free radicals during the asparagine/glucose Maillard reaction, which oxidized the lipid and facilitated its reaction with the amino acid. These results suggest that both unoxidized and oxidized lipids are able to contribute to the conversion of asparagine into acrylamide, but unoxidized lipids need to be oxidized as a preliminary step.