In order to examine the correlation between open-tube melting point and polymorphism in the raw material oils and fats, measurement were made on seven samples of palm oil, coconut oil, hardened soybean oil, beef tallow, lard (bak and abdomen), and hardened whale oil after standing at 0, 10, 20, 30 and 40°C for 1, 5, 24, 120 and 480 hours.
1) The higher the standing temperature, polymorphism progressed more, approaching to the stable form, with rise in the melting point. When left at a low temperature, polymorphism did not progress and the melting point tended to be lower.
2) Fatty oils and hardened oils of high melting point showed slow polymorphism, and the modification starts from the unstable form. Consequently, the melting point tends to be lower.
3) Glycerides of high melting point, of symmetric type, exhibit fast polymorphism but those with complex composition of fatty acids or with a long molecular chain exhibit polymorphism. From this reason, transition occurred in the descending order of lard, palm oil, and beef tallow, and the difference in the melting point according to the standing temperature was greatest in the case of beef tallow.
4) Scattering of the melting point seemed to differ according to the kind of the fats and oils used as the raw material but it became smaller as the standing temperature became higher and as the time of standing longer.
5) When the SFI values are smaller, there is smaller degree of twinning of the molecules themselves and the form of the molecule tends to become straight, and the molecule becomes easier to line up when growing from the nucleus. Consequently, transition rate becomes faster and the melting point tends to be higher than those left at lower temperatures.
