Formation of β-phenylethylamine as a consequence of lipid oxidation

The decarboxylation of phenylalanine in the presence of methyl 13-hydroperoxyoctadeca-9,11-dienoate (LOOH), 2,4-decadienal (DD), 4,5-epoxy-2-decenal (ED), 4-hydroxy-2-nonenal (FIN), and 4-oxo-2-nonenal (ON) was studied both to explore the potential of lipid oxidation products (LOP) to produce amino acid decarboxylation and to understand the reaction pathways responsible for this degradation. All assayed LOP were able to decarboxylate phenylalanine, but their reactivity decreased in the following order when the reaction was carried out under non-oxidative conditions: DD > ED approximate to LOON > HN approximate to ON. The reaction pathway is proposed to take place by decarboxylation of the imine formed between the amino group of the amino acid and the carbonylic group of the oxidized lipid. This decarboxylation is facilitated due to the formation of a relatively stable azomethine ylide after the loss of carbon dioxide from a 5-oxazolidinone intermediate. The azomethine ylide would, finally, evolve into new conjugated imines, which are the origin of both beta-phenylethylamine and phenylacetaldehyde, which was also detected in the reaction mixtures. The activation energy (Ea) for the phenylalanine decarboxylation in the presence of 2,4-decadienal was 54 kj/mol. Although additional studies are needed to determine the contribution of the chemical pathways described in this study to the overall biogenic amine formation in foods, this study provides the chemical basis both to understand how biogenic amines can be produced chemically from amino acids in the presence of lipid-derived carbonyls and to propose potential inhibitors in this route. (C) 2012 Elsevier Ltd. All rights reserved.