Analysis of free malondialdehyde in photoirradiated corn oil and beef fat via a pyrazole derivative.

Malondialdehyde (MA) formed in linolenic acid, linoleic acid, corn oil and beef fat upon photoirradiation was determined by gas chromatography (GC). The MA produced was reacted with methylhydrazine to give 1-methylpyrazole and was subsequently analyzed on a GC equipped with a nitrogen-phosphorus specific detector and a fused silica capillary column. MA values determined by this method correspond to free or unbound MA levels. Linolenic and linoleic acids produced 867 micrograms MA/g and 106 micrograms MA/g, respectively. Oleic and stearic acids did not produce detectable levels of MA upon photoirradiation. Amounts of MA produced after eight hour irradiations of corn oil and beef fat were 56.24 micrograms/g and 25.01 micrograms/g, respectively. Some photoreaction products in irradiated corn oil also were identified as methylhydrazine derivatives.