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The aims of dissertation are: (1) to investigate the influence of calcium ions and saponins on solubilization of cholesterol at conditions, simulating the digestive tract and (2) to clarify the mechanisms behind the observed effects, by using colloid and bio-physical methods. The main conclusions of the dissertation can be summarized as follows: 1. We found that the solubilization of cholesterol, fatty acids and monoglycerides decreases with increasing calcium concentration in the reaction mixture, simulating the intestinal fluid in the digestive tract. We confirmed that the main mechanism by which calcium ions decrease cholesterol solubilization in mixed micelles of bile salts and reaction products, is by precipitation of fatty acids and monoglycerides. 2. We found that the active components for cholesterol-lowering in the Quillaja Dry extract (QD) are not the saponins, but the large molecular-weight polyphenols, present in this extract. It was shown also that the solubilization of saturated fatty acids in the dietary mixed micelles decreases significantly in presence of QD. This effect is explained by the presence of calcium ions of high concentration in the QD. 3. We found a new saponin extract (Sapindin), which decreases cholesterol solubilization in vitro and prevents prevents the increase of serum cholesterol in in vivo experiments with mice. There is good semi-quantitative agreement between the cholesterol bioaccessibility, measured in vitro, and the serum cholesterol levels determined in vivo. The main mechanism of lowering the cholesterol bioaccessibility by Sapindin is via displacement of cholesterol from the dietary mixed micelles, leading to formation of cholesterol precipitates.
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