Experiments for prevention of hardened coconut oil series deterioration were made with four kinds of sugar fatty acid esters, monoolein, monolinolein and propylene glycol esters of fatty acids.
1) Sugar fatty acid esters, ranging from lipophilic ones containing a large amount of triester to hydrophilic ones with a larger content of monoester, were added by 1-2%. Rise in A.V. was hardly observed in samples added with sugar esters containing a large amount of triester. There were some effect in other esters but the rise in A.V. occured with decrease in the content of triester.
2) Examination of the crystal surface showed the presence of minute single crystals in the sample added with lipophilic sugar ester with low triester content, but the surface was much more smooth than that of the control sample without the addition. Sample added with lipophilic sugar ester and which did not show rise in A.V. was a non-crystalloid and had smooth surface.
3) Addition of monoolein or monolinolein could prevent the increase in A.V. up to a certainextent. Electron microscopic observations on crystal surface of such samples exhibited more smooth than the control samples without such addition.
Propylene glycol ester of fatty acid was practically ineffective in preventing the crystal growth.
