Samples of coconut oil (I.V. 9.9), hardened coconut oil (I.V. 1.6), and coconut oil mixed with 5 or 20% of fully hardened beef tallow (I.V. 1.4) and samples obtained by randomly interesterification among these samples were stored at 5, 15 and 30 C for 6 months, and their A.V., P.O.V. and Co.V. were measured every month. Roughness of their crystal surface was examined by electron microscope and correlation between crystal growth and change in A.V. was also examined.
1) As the criteria for judging completion of ester exchange, measurement of the melting point, S.F.I. curve and cooling differential thermal analysis were carried out.
2) No great change was seen in P.O.V. and Co.V. in the original samples and those obtained by ester exchange, but they all underwent change with the rise in storage temperature, showing that P.O.V. and Co.V. had no correlation with the glyceride composition.
3) As reported in the previous paper, the original samples showed no change when stored at 30 °C but A.V. increased by storage at 15 and 5 °C, in that order, and this change was greater in the sample mixed with hardened beef tallow. Samples obtained by interesterification showed no rise in A.V. at all the temperatures of storage tested.
4) Roughness of crystal surface under electron microscope became greater when stored at 15 and 5 °C, in that order, while the samples obtained by interesterification showed a smooth surface in all the samples kept at any of the temperatures tested. It was thereby found that low temperature deterioration characteristic to hardened coconut oil can be prevented by changing the glyceride composition.
