6, 326 [ 19551. 52 M. van den Tempel, J. Colloid Sci. 16,284 [1961]. 53 A. J. Haighton, Fette . Seifen . Anstrichmittel 65, 479 119633. 54 A. J. Haighton, J. h e r . Oil Chemists' SOC. 42,27 [1965]. Danksagung rung der Arbeit. Eingegangen am 7. Juli 1988. Der H. Wilhelm Schaumann-Stiftung danken wir fiir die Forde-High Performance Size Exclusion Chromatography of Polar Compounds in Heated and Non-Heated Fats Fat Sci. Technol. 90. Jahrgang Nr. 8 1988

Virgin olive oils were subjected to simulated common domestic processing, including frying, microwave heating, and boiling with water in a pressure cooker. The impact of these processes on polyphenol content and physicochemical characteristics of oils was assessed. Thermal oxidation of oils at 180 degrees C caused a significant decrease in hydroxytyrosol- and tyrosol-like substances. In contrast, oils heated for 25 h still retained a high proportion of the lignans 1-acetoxypinoresinol and pinoresinol. Thermal oxidation also resulted in a rapid degradation of alpha-tocopherol and the glyceridic fraction of oils. Microwave heating of oils for 10 min caused only minor losses in polyphenols, and the oil degradation was lower than that in thermoxidation assays. Again, lignans were the least affected polyphenols and did not change during microwave heating. Boiling a mixture of virgin olive oil and water in a pressure cooker for 30 min provoked the hydrolysis of the secoiridoid aglycons and the diffusion of the free phenolics hydroxytyrosol and tyrosol from the oil to the water phase. Losses of polyphenols were detected only at pH lower than 6. Moreover, alpha-tocopherol and the glyceridic fraction of oils were not modified during this process. It is worth noting that all the heating methods assayed resulted in more severe polyphenols losses and oil degradation for Arbequina than for Picual oil, which could be related to the lower content in polyunsaturated fatty acids of the latter olive cultivar. These findings may be relevant to the choice of cooking method and olive oil cultivar to increase the intake of olive polyphenols.

The risk of hypertension is positively and independently associated with the intake of cooking oil polar compounds and inversely related to blood concentrations of monounsaturated fatty acids.

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The objective of this work was to study the evolution of oxidation in sunflower oils differing in unsaturation degree during long-term storage at room temperature. For this purpose, a combination of adsorption and size-exclusion chromatographies was used for quantification of oxidized triacylglycerol (TG) monomers, dimers, and polymers. Conventional sunflower oil, genetically modified high-oleic sunflower oil, and a 1:1 mixture of the two were used. Results showed that oxidized TG monomers were the only group of oxidation compounds increasing during the early oxidation stage, and an excellent correlation was found between amounts of oxidized TG monomers and PV during the induction period, independently of the degree of oil unsaturation. Both the rate of formation and the amount of oxidized TG monomers accumulated at the end of the induction period increased as the unsaturation degree of the oils tested was higher. The end of the induction period was marked by the initiation of polymerization and exhaustion of tocopherol. Therefore, the concomitant determination of oxidized TG monomers and polymerization compounds provided a complete picture of the oxidation process.

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A description is given of the development by collaborative study of two standardized methods for the determination of polar compounds in oils and fats by adsorption chromatography using silica minicolumns, and for quantification of polymerized triacylglycerols, oxidized triacylglycerols, and diacylglycerols in polar compounds by high-performance size-exclusion chromatography. The first procedure is sensitive, allowing savings in time, solvents, and reagents as compared to the previous determination (Standard Method 2.507), while the second is very rapid, giving a detailed information on the main groups of compounds in fats and oils associated with hydrolysis, oxidation, and thermal polymerization. Both methods are useful for the analysis of used frying fats as well as for the analysis of virgin or refined oils.