In the case of lipid oxidation through air at 180°C for 2 hours in glass flask, the increase of 1750cm-1 estercarbonyl absorption was observed in the infra red spectrum and the high electron spin resonance peak was detected. Such increasing absorption and high peak gave the information that the radical polymerization and peroxidation of lipid mainly occurred, though little carbonylization took place via the peroxidation (peroxide). While, the addition of 1% sesamol to the oxidation condition described above brought about the appearance of a new carbonyl absorption (1730cm-1) together with the increase of 1750cm-1 absorption. Especially, triolein of a pure triglyceride gave the typical pattern in the infra red spectrum, which was same pattern as observed in the electron spin resonance. From the change of the infra red spectrum and electron spin resonance, the degrees were indicated of the carbonylization and polymerization of lipid under such drastic oxidation as the addition of sesamol.
In the preceding report, from the information of infra red spectrum and electron spin resonances, it was suggested that the oxidation of lipid gave the polymerization and peroxidation products mainly under the mild condition of heating, but addition of sesamol induced the carbonylization from the peroxidation. In this paper, the oxidation of lipid under the condition of heating on the metal surface was reported. In some cases of the oxidations, the new carbonyl absorptions (1730cm-1) appeared in the infra red spectrum that showed the carbonylization from the peroxides. Especially, in the oxidation of triolein on the iron surface, the increase of the absorption (1730cm-1) in infra red spectrum was parallel with the decrease of the peroxide value. Moreover, the degree of the absorption (1730cm-1) was largely effected by the kind of metal. The oxidation on tin generated the strong absorption of 1730cm-1 in the infra red spectrum. On the other hand, in many cases of the oxidations on iron, the absorptions were not observed. These results suggested the useful application of infra red spectrum to studing the oxidation of lipid by the metal catalyst at high temperature. Under the condition as described above, electron spin resonance peak was not detected in the almost cases.
For the determination of nicotinic acid (NA) in foods, the following result was obtained by high-performance liquid chromatography with Zipax SCX column. The method was useful for the detection of NA in foods. Calibration curve was linear over the range 0-100μg/ml of NA and minimum detectable concentration was 5μg/ml. Adjustment of pH value of the sample solution to pH value of mobile phase, 2.6 was required.