Strecker Type Degradation of Phenylalanine by 4-Hydroxy-2-nonenal in Model Systems

The reaction of 4-hydroxy-2-nonenal, an oxidative stress product, with phenylalanine in acetonitrile-water (2:1, 1:1, and 1:2) at 37, 60, and 80 degrees C was investigated to determine whether 4-hydroxy-2-alkenals degrade amino acids, analogously to 4,5-epoxy-2-alkenals, and to compare the reactivities of both hydroxyalkenals and epoxyalkenals for production of Strecker aldehydes. In addition to the formation of N-substituted 2-pentylpyrrole and 2-pentylfuran, the studied hydroxyalkenal also degraded phenylalanine to phenylacetaldehyde with a reaction yield of 17%. The reaction mechanism is suggested to be produced through the corresponding imine, which is then decarboxylated and hydrolyzed. This reaction also produced a conjugated amine, which both may be one of the origins of the produced 2-pentyl-1H-pyrrole and may contribute to the development of browning in these reactions. 4-Hydroxy-2-nonenal and 4,5-epoxy-2-decenal degraded phenylalanine in an analogous extent, which is likely a consequence of the similarity of the degradation mechanisms involved. These results suggest that different lipid oxidation products are able to degrade amino acids; therefore, the Strecker type degradation of amino acids produced by oxidized lipids may be quantitatively significant in foods.