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Purified triolein (TO) and trilinolein (TL) were oxidized by introducing oxygen at 75°C into the same apparatus as employed previously. In each oxidized sample, volatile decomposition products, especially aldehydes (as the origin of rancid odor), were identified by gas chromatography mass spectrometry, comparing with the products from the corresponding fatty acid methyl-ester.It was observed that heptane and octane as hydrocarbons, 1-heptanol and 1-octanol as alcohols, and heptanal, octanal, nonanal, decanal, 2-decenal and 2-undecenal as aldehydes were formed from TO, while pentane as a hydrocarbon and hexanal, heptanal, 2-heptenal, 2-octenal and 2, 4-decadienal as aldehydes were obtained from TL. The precursors of those products, the monohydroperoxides (MHP), and cleavage positions were discussed in comparison with those of methyl-esters. The formation mechanism of the above products could be explained except for heptanal from TO and 2-heptenal from TL (these were assumed to be secondary oxidation products). Further, 3-nonenal (or 2-nonenal), which was expected to be formed from TL, was not found. In the oxidation of TL, formation of 11-MHP was found in addition to 9-MHP and 13-MHP.The relative percentages of peak area were calculated from a gas chromatogram of volatiles derived from TO, and aldehydes accounted for about 67% of the area. The odor of octanal was the strongest. In the oxidation of TL, 2, 4-decadienal accounted for 42% of the total area, and the odor of hexanal was the strongest at each stage of oxidation.

To examine the autoxidation of unsaturated triglycerides, experiments were carried out on purified trilinolein (TL), by introducing oxygen at 75°C into an apparatus similar to that employed previously. Methyl linoleate (ML) prepared from the same source was used for comparison. Samples were taken at various oxidation times, and several chemical constants such as peroxide value (POV), thiobarbituric acid value (TBAV), etc. were measured. The IR and UV absorption spectra were also examined. Further, the antioxidative effect of α-tocopherol (α-Toc) and the synergism of ascorbic acid (AA) were studied. α-Toc and AA (3mM/kg) were added TL, and the residual amounts of them in the course of oxidation were followed by high performance liquid chromatography. The relation between the decrease of residual α-Toc and AA and the increase of POV of TL was examined.The results obtained were as follows. The induction period of oxidation was much shorter in TL than in ML. The rate of oxidation or decomposition of peroxides was faster in TL than in ML after the induction periods. The maximum TBAV of TL was found to be about 1/3 that of ML. The antioxidative effect of α-Toc and the synergistic effect of AA were clearly observed in both TL and ML. It was observed that α-Toc and AA decreased more gradually when both were present than either one alone. The results indicate that α-Toc and AA acted as mutually protective substances, and when both disappeared at nearly the same time, POV increased rapidly.

A simple method for the determination of sorbic acid in foods was presented. The method was based on the following two steps: The separation of sorbic acid by steam distillation from foods and subsequent colorimetric determination.The procedure was as follows: One ml of the distillate containing 50-400μg of sorbic acid was transferred into a 20ml graduated test tube, and diluted to the 20ml mark with 0.2% p-hydroxybenzaldehyde-sulfuric acid solution. After the solution was kept in a boiling water bath for 20 minutes, and cooled under tap water, the absorbance of the resulting solution was measured spectrophotometorically at 610mμ.The recoveries of sorbic acid from food were 95.3-99.8%.