Protein- saponin interaction and its influence on blood lipids

Protein source and saponins have been shown to influence lipid metabolism; however, little is known regarding the chemical interactions between proteins and saponins or the impact of addition of dietary saponins to different proteins on cholesterolemia. In the present study, quillaja saponin was added to casein and to isolated soy protein (ISP) and the saponin-protein interaction was investigated by gel electrophoresis and fluoroscopy. The impact on cholesterol metabolism also was investigated in gerbils. Results from the interaction studies showed that high molecular weight complexes were formed gradually between saponins and caseins, with β-casein being most susceptible. The resulting complexes differed drastically in charge and molecular weight. In contrast, soy proteins formed insoluble aggregates during heating independently of the presence of added quillaja saponin. Data from the animal study showed that addition of saponin to ISP did not affect serum lipids, while addition of saponin to casein resulted in significant decreases of LDL cholesterol and LDL/HDL ratios, resulting in values similar to those of ISP-fed animals. These results indicate that the effect of saponins on serum lipid profiles is dependent on the source of dietary protein. This could be explained by the finding that quillaja saponin reacted differently with caseins as compared to soy protein isolate.