Open-tube melting point and polymorphism were measured with five kinds of soybean oil and four kinds of beef tallow of different degrees of hardening, which were allowed to stand at 0, 10, 20, 40 and 50°C for 1, 5, 15, 24, 120 and 480 hours. Correlation of these points with S.F.I. and composition of fatty acids was also investigated.
1) In hardened soybean oil, polymorphism was later for the higher degree of hardening and for the lower temperature. In extreme hardening #0, polymorphism was entirely absent whn lfet at 0 and 20°C, and there recognized nearly no change in the melting point. With #20 (I.V. 17.1) and #40 (I.V. 38.9), the polymorphism was practically absent when left at 0°C, taking β-form when left at 40°C for 15 and 24 hours, and difference in the melting point due to time and temperature was also great. With #60 (I.V. 58.4) and #80 (I.V. 81.3), the polymorphism was much faster.
2) Hardened oil contains a considerable amount of C18 ;1 trans acid, therefore, the S.F.I. values became greater as the degree of hardening became higher and as the temperature of standing became lower. The S.F.I. value was 100% in #0 and #20, and over 50% in #40. Polymorphism was slow.
3) Hardened beef tallow also showed the same tendency as the hardened soybean oil but the poly-morphism was generally slower than that of soybean oil. Consequently, difference in the melting point due to the time and temperature of standing was smaller.
4) The amount of trans acid in beef tallow is smaller than that in hardened soybean oil and the value of S.F.I. is smaller, except in #0. The slower polymorphism of beef tallow than that of soybean oil is considered to be due to the complex composition of the glycerides and fatty acids
