Differential Thermal Analysis of Edible Fats and Oils. II

Abstract

Heating differential thermal analyses were carried out, as previously reported, on four kinds of coconut oil and four kinds of palm kernel oil of different degree of hardening, comparing variation in the curve by the degree of hardening with the open capillary melting point and polymorphism measurment.1) Coconut oil stored at 0°C only showed a large and sharp endothermic peak at 24°C, irrespective of the degree of hardening and duration of standing. When coconut oil was left at 20°C for 1 hour, a small endothermic peak appeared at 19°C besides the peak at 24°C, and the smaller peak became sharp with lapse of time of standing.2) Coconut oil stored at 20°C for 1, 440 hours (two months) showed further changes in the curve, the peaks becoming more complex as the degree of hardening advanced, unhardened coconut oil #8 (I.V. 8.0) and #5 (I.V. 4.9) showing three peaks, #2 (I.V. 2.2) four peaks, and #0 (I.V. 0.7) five peaks. Polymorphism was a β′ type, which did not change greatly with difference in the degree of hardening, period or temperature of standing, but was different in the open capillary melting point. These facts agree with the result of DTA.3) The DTA curve of palm kernel oil showed greater variation than that of coconut oil, and the curves of #5 (I.V. 5.0) and #0 (I.V. 0.6) showed considerable change after ;standing at 0°C. When stored at 20°C for 1 hour, the curve was the same as that of coconut oil. The variation was greater, the longer the period of standing and higher the degree of hardening.Polymorphism of palm kernel oil was also similar to that of coconut oil, the transition being late, and there was no difference according to the temperature of standing, but showed considerable difference in the open capillary melting point, which was contrasted with the result of a marked difference in DTA curves.