Effect of Processed Oils and Fats on Cholesterol Metabolism. IV

Effect of Palm Stearin and Changes in Its Effect by Blending with Soybean Oil and Further Randomizing

Abstract

Four groups of weanling male rats were fed diets containing 20% (by weight) either palm stearin, soybean oil, their equal weight blend (PS/SO) or fat randomized blend [(E)PS/SO] for 28d. A comparative study was made of serum lipids, cholesterol and its metabolites in the livers and feces of the rats. The physical and chemical properties of the dietary fats were also examined.
1) SFC curves indicated palm stearin rich in saturated triglycerides, mainly tripalmitin, to be considerably hard even at 30°C. However, its blend with soybean oil and further randomization improved plasticity and mouth feel due to decrease in SFC at each step.
2) Serum cholesterol (total) and triglyceride concentrations were significantly higher in the palm stearin group, but similar in the PS/SO and (E)PS/SO groups, compared with those in the soybeanoil group. In the palm stearin, PS/SO and (E)PS/SO groups, C_{16 : 0} rich in dietary fats was preferentially excreted into feces, but the proportion of this fatty acid in liver lipids of the palm stearin group was obviously higher than those of the PS/SO and (E)PS/SO groups.
3) Contents of cholesterol and its metabolites in the feces were basically the same among the palm stearin, PS/SO and (E)PS/SO groups. In contrast, contents of some metabolites, formed by the action of intestinal bacteria, such as coprostanol and deoxycholic acid, in the palm stearin group werelower than those of the other two groups. Thus, the ratio of metabolites to cholesterol in the feces was low only in the palm stearin group, while no differences could be detected among the PS/SO, (E)PS/SO and soybean oil groups.
4) Plam stearin, uniquely rich in C_{16 : 0,} especially in tripalmitin, thus appears to have adverse effect on serum cholesterol, probably due to increase in C_{16 : 0} incorporated into liver, and cholesterol metabolism due to the suppression of intestinal bacteria functions. However, blending palm stearin with liquid vegetable oils and randomization were shown to improve both physical and biological properties.