Lipid oxidation in aqueous systems is active area of research because lipids are present in aqueous medium in many food systems and in biological systems. Oxidative stability of polyunsaturated lipids generally decreases with increasing the degree of unsaturation, however, the stability in an aqueous solution is quite different from that in bulk phase or in organic solvent. In aqueous micelles, the oxidative stability of lipids increases with increasing the degree of unsaturation, and in emulsion, lipid oxidation is greatly affected by the properties of interface that consists of emulsifier and lipid. What is the reason for this characteristic behavior of the lipids in aqueous systems? NMR analysis gives useful information that more unsaturated fatty acids have higher flexibility of acyl chain conformation in aqueous systems. This flexibility brings about its high water permeability. The presence of water molecule near acyl moieties decreases the density of bis-allylic positions, where hydrogen radical abstraction occurs at the start of lipid oxidation; therefore, more unsaturated fatty acids is oxidatively more stable than less unsaturated fatty acids in aqueous micelles. Polyunsaturated fatty acyl moieties show the same behavior in other aqueous circumstances such as liposomes and cellular membrane to result the different oxidative stability from bulk phase and organic solvent system.

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The analysis of triglyceride (TG) molecular species in naturally occurring fats and oils by HPLC and LC-MS was investigated based on the partition number theory. The method using the tandem joined HPLC-UV-ELSD system with gradient elution was developed to quantify the respective TG molecular species in the fish oil. The position of DHA in the TG of a marine lipid was analyzed by the NMR method, and the procedure was established as one of the official analytical methods of the Japan Oil Chemist Society (JOCS). Additionally, the preservation of food lipids using an antioxidant like tocopherol, rosemary extract and phytic acid and its hydrolysis products for marine lipids are summarized. The Japanese traditional marine product of dried bonito, 'Katsuobushi' was examined for any lipid change during processing. The oxidized fats and oils are also reported to be a neurotoxin problem. Consequently, the control of the oxidation of fats and oils in foods is important, in order to prevent the deterioration of foods and protect human health in conjunction with the TG molecular species analysis.

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