The hydrolysis of thermally oxidized sunflower oil by pancreatic lipase was studied in relation to chemical changes in the acylglycerols. Four classes of compounds (monomers, dimers, trimers and polymers) formed from the acylglycerols were separated from the heated oils by column chromatography on silica gel, and further verified by thin layer chromatography. Each fraction, after analyses for generaly properties, was subjected to a time course study of hydrolysis by pancreatic lipase over a 30-min period. After 70 hr of heating, the amount of hydrolysis for the acylglycerol dimers was only about half that of the monomers, and that for the trimers was, in turn, about one-third that of the monomers. The polymers were the least hydrolyzed and showed no further reaction after 5 min. The reduction in enzymatic hydrolysis of isolated fractions from the thermally oxidized oils indicates structural differences, related to formation of polar compounds and polymerization products. Adverse effects on animals from feeding these materials can be attributed partly to inhibition of hydrolysis resulting in less available energy.

Butter, butterfat, and corn, coconut, rapeseed, and soybean oils were exposed to 500 ft-c of fluorescent light at varying time-temperature conditions. Oxidation rates were measured by the peroxide values. Vitamin A and ~-carotene content of butterfat were estimated. The effect of wavelength on the relative rates of oxidation was determined. The light transmitting properties of the samples at 15 and 30 C over a spectral range of 380-750 nm were measured. It was observed that there was no increase in oxidation rate when the light was switched off. The stability of the oils as shown by the oxidation rates did not correlate well with the ratios of C18:2 to C18:1 or C18:3 to C18:2 nor with the degree of unsaturation. Increase in temperature alone had minimal effect; however, in the presence of light the rate of oxidation increased considerably with a corresponding decrease in the content of Vitamin A and ~carotene. ~-Carotene provided strong protective properties. After the photobleaching of ~carotene in butterfat, there was a rapid increase in peroxide values. With coconut oil, the oxidation rate was greater at 15 C than at 30 C due to greater light absorption at 15 C over the entire spectrum. The rate of oxidation decreased at higher wavelengths, and this effect was more pronounced in the vegetable oils than in butterfat, where the /3carotene was considered to serve as a filter for light of low wavelength.

No abstract

Methyl linoleate, diluted with an equal weight of methyl laurate, was heated without exclusion of air at 200C for 200 hours. The reaction mixture was separated by means of molecular distillation, urea adduction, column chromatography, and gas chromatography. Cyclic and aromatic materials were detected in the nonurea adductable monomer fractions. The dimer was separated into polar and nonpolar fractions. Analytical data for the nonpolar dimer are consistent with a cyclic Diels-Alder product. Bioassays showed the nonadductable monomer, the polar dimer, and a fraction of intermediate boiling point to be toxic when administered to weanling male rats. Urea-adductable fractions, nonpolar dimer, and polymer were not toxic. The concentrations of the toxic components were so low that the heated linoleate, before fractionation but after removal of the laurate, was not toxic.