Induction Periods for Lipid Crystallization of Various Vegetable Oils.

The induction period for crystallization, defined as the time required to crystallize, was discussed during isothermal storage at -5 to -45°C for various vegetable oils; olive, safflower, rapeseed, corn, rice bran, soybean, and linseed oils. The induction periods, largely dependent on the oil type and storage temperature, were classified into two groups. The induction periods of corn, rice bran, soybean, and linseed oils were monotonically shortened as the storage temperature decreased. On the other hand, the induction periods for rapeseed, olive, safflower oils and the mixtures of rapeseed and soybean oils, and of olive and safflower oils did not simply change or elongate with a decrease in storage temperature. The induction periods could be formulated using two parameters. One was an expected value of the melting point of the oil, which was calculated from its fatty acid composition. The other was a molar fraction of triacylglycerol composed of the same fatty acids in the oil. The crystallization and melting processes of the oils under nonisothermal conditions were also analyzed by differential scanning calorimetry (DSC). It was suggested that the induction period was also predictable from the peak shape, peak number, onset temperature, and peak area in the DSC curve of the oil during the crystallization process.