Chemical conversion of phenylethylamine into phenylacetaldehyde by carbonyl-amine reactions in model systems

The chemical conversion of phenylethylamine into phenylacetaldehyde in the presence of lipid oxidation products (LOPs) was studied to investigate the possibility that biogenic amines can be converted into Strecker aldehydes upon processing. Model systems of phenylethylamine and methyl 13-hydroperoxyoctadeca-9,11-dienoate (HP), 2,4-decadienal (DD), 4,5-epoxy-2-heptenal (EH), 4,5-epoxy-2-decenal (ED), 4-oxo-2-hexenal (OH), 4-oxo-2-nonenal (ON), or 4-hydroxy-2-nonenal (HN) were heated for 1 h at 180 °C and pH 3. Although HN and EH did not produce more phenylacetaldehyde than when phenylethylamine was heated alone, all other lipid oxidation products assayed increased the amount of phenylacetaldehyde produced by 300-900%, with ON being the most reactive compound for this reaction. The reaction was mainly produced at acidic pH values (<6) and was dependent upon the concentration of the LOPs involved, and the phenylacetaldehyde produced increased linearly as a function of the time and temperature. The E(a) values for the reactions between phenylethylamine and DD and ON were 54.8 and 53.8 kJ/mol, respectively. The reaction is proposed to take place by the formation of an imine between the phenylethylamine and the LOPs, which is later converted into another imine by an electronic rearrangement. This new imine is the origin of phenylacetaldehyde by hydrolysis. These results show a new pathway for Strecker aldehyde formation. This route provides a potential way to reduce biogenic amine content in foods when they can be thermally processed before consumption.