High‐performance liquid chromatography and spectroscopic studies on fish oil oxidation products extracted from frozen atlantic mackerel

Abstract

AbstractThe formation of stable hydroxy derivatives from hydroperoxides produced during the oxidation of linoleic acid methyl ester and fish oil were studied by reverse‐phase high‐performance liquid chromatography (HPLC), gas chromatography‐mass spectrometry (GC‐MS) and 13C nuclear magnetic resonance (NMR) spectroscopy. The oxidation products identified were mixtures of four isomeric hydroxy derivatives: 13‐hydroxy‐9‐cis,11‐trans‐octadecadienoic, 13‐hydroxy‐9‐trans,11‐trans‐octadecadienoic, 9‐hydroxy‐10‐trans,12‐cis‐octadecadienoic, and 9‐hydroxy‐10‐trans,12‐trans‐octadecadienoic acids. The presence of hydroxy compounds was confirmed by 13C NMR, which gave rise to a hydroxy carbon peak at 87 ppm, and by GC‐MS, which showed three peaks corresponding to isomeric mixtures of trimethylsilyl ethers of the oxidized linoleic acid methyl ester. The mass spectra scans of the three peaks showed that they represent isomers of molecular weight 382 and are consistent with the molecular formula C22H42O3Si. In oil extracted from stored frozen mackerel, 13‐hydroxy‐9‐cis,11‐trans‐octadecadienoic acid was more prominent compared to the model lipid systems. HPLC offered a sensitive means of detection of hydroxy compounds produced both in the initiation and latter stages of oxidation. The effect of antioxidants added to the fish mince prior to storage can also be monitored by HPLC. Thus, the monitoring of lipid oxidation hydroxy derivatives by HPLC is of practical value in the efficient processing and quality control of fish, fish oils, and other fatty foodstuffs in order to enhance the acceptability, nutritional, and safety aspects.