Effects of Trans Isomers in thermally Oxidized Lipids on the Formation of Lipid-Protein Complexes

Abstract

Cottonseed oil, methyl oleate and methyl linoleate were oxidized at various temperatures ranging between 0 and 180°C for 24hr with aeration. They were then treated with egg albumin in an aqueous medium under the atmosphere of nitrogen at 60±2°C for 2hr with agitation at the rate of about 250rpm. The lipid-protein complexes and unreacted lipid fractions were isolated and such lipid fractions were compared with the oxidized lipids originally used.It was confirmed that only the lipid materials which had been oxidized to a sufficient degree formed complexes with protein. In all cases, however, the maximum level of lipids contained in the complexes was considerably limited : utmost 1.3%, 0.3%, and 0.3% on a weight basis, for oxidized cottonseed oil, methyl oleate and methyl linoleate, respectively. The refractive indices, viscosities, iodine values and peroxide values were failed to give information on the possible mechanism of the complex formation.The amounts of lipids contained in the complexes are approximately constant when the lipid-protein complexes are formed with cottonseed oil, methyl oleate and methyl linoleate oxidized at or above 90, 120, 30°C, respectively. But in the complex formed with methyl linoleate oxidized at 180°C, this value is small. Total trans isomers contents in oxidized cottonseed oil, methyl oleate and methyl linoleate are approximately constant when the lipids are oxidized at or above 90, 120 and 60°C, respectively. But in methyl linoleate oxidized at 180°C, this value is small. These facts show that there is an intimate relationship between total traps isomers produced in thermal oxidation of lipids and lipid-protein complex formation.