Identification of N-epsilon-(2-propenal)lysine as the main form of malondialdehyde in food digesta.

The form(s) in which malondialdehyde (MDA), a mutagenic product of the oxidative decomposition of polyunsaturated fatty acids (PUFA), occurs in foods was investigated. Several foods of animal origin (ground beef, smoked fish, chicken, sausages) were digested in vitro using pepsin and porcine intestinal fluid and the occurrence of MDA derivatives in the digesta was investigated by thin-layer, column and high-performance liquid chromatography. The predominant form of MDA was shown to be identical to synthetic N-epsilon-propenal lysine. This compound is apparently formed by a reaction between free MDA generated as a product of the oxidative rancidity of PUFA in foods and the free epsilon-amino groups of proteins, from which it is released in the course of digestion. It has been shown to be excreted in rat and human urine partially in the unchanged form and partially as the N-alpha-acetyl derivative. The results of this study serve to mitigate concern over the possible carcinogenicity of MDA in the diet, since less than 10% of the MDA in several foods containing highly unsaturated fatty acids was found in the free form.