抄録
It was found that the low-temperature deterioration of hardened coconut oil series was due to strong adsorption of water on the active surface during crystal growing. It was expected that oxygen would also be adsorbed at the same time and, therefore, experiments were made on the addition of β-carotene which is relatively affected by oxidation. The oils added with β-carotene were stored at 5°, 15° or 30°C for 2 months, there by the A.V., P.O.V. and residual rate of β-carotene were measured. Color tone was examined by the Rovibond method and absorbance was measured at 450 mμ.
1) Coconut oil series stored at 5° or 15°C showed an increase in A.V., accompanied by green coloration but such coloration was not observed in the oil stored at 30°C, and in the control samples of hardened soybean oil and hardened whale oil which were stored at 15°C.
2) Measurement of the amount of β-carotene showed that the residual quantity decreesed in the order of increase in A.V. and green coloration. The decrease was especially marked in hardened palm kernel oil, the residual β-carotene being nil after 2 months of storage at 5° or 15°C.
3) Residual color estimated from absorbance at 450 mμ also showed the same tendency but the residual rate of β-carotene was rather large. It was therefore considered that changes in color were due to the formation of an oxidation intermediate.
4) Colored substance was separated from β-carotene by column chromatography and submitted to thin-layer chromatography. The chromatogram revealed yellow, greenish, orange and bluish green spots, which were considered to be oxidation products, other wise than the spot for β-carotene.
5) Absorption spectra in the visible range were measured with each of the fractions separated by thin-layer cnromatography. The spot at Rf 0.56 had large absorption maxima at 426 and 451 mμ, and a small absorption at 405 mμ. The spot at Rf 0.20 was labile and its spectral measurement could not be made. These spots were considered to be the main components of the green-colored substance.
