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The effect of dried oyster mushroom (Pleurotus ostreatus) on cholesterol (C) content in serum, in lipoproteins and in liver, and on the activity of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase in liver microsomes, was studied in male rats (strain Wistar, initial body weight 75 g) fed on low-cholesterol (9 mg/100 g) and high-cholesterol (0.3%) diets. Addition of 5% oyster mushroom to both diets reduced significantly the C-content in serum (by 30%), in very-low- and low-density lipoproteins (in a 1:1 ratio to the decrease of total serum C) and in liver (by 50%), as well as the activity of HMG-CoA reductase (by more than 30%).

The effect of dried tomato, grape and apple pomace (5% in diet) on the cholesterol levels in serum and selected organs was studied in male Wistar rats fed a cholesterol diet (0.3%) shortly after weaning. Pomace of individual fruits contained 47.2, 67.0 and 46.2 g of total dietary fiber per 100 g of dry matter for tomato, grape and apple pomace, respectively. Corresponding values for the soluble components of the fiber were 10.3, 14.7 and 26.0%. None of the tested products affected the serum cholesterol levels. Tomato and apple pomace significantly reduced cholesterol level in liver by 15% and 11%, respectively, and all tested pomace species reduced cholesterol content in heart (by 18-21%). Triacylglycerol content was affected only by tomato pomace and solely in the heart. Cholesterol absorption measured by dual-isotope ratio method, was not significantly affected by the pomace, however, all products strongly reduced (up to the half of the original value) the activity of HMG-CoA reductase in liver and increased the fractional catabolic rate of plasma cholesterol (by 60-120%). All tested pomace reduced plasma levels of conjugated dienes and tomato and grape pomace exhibited this effect also in the liver. All tested pomace reduced the activities of antioxidant enzymes superoxid dismutase, catalase and glutathione peroxidase in erythrocytes (by 34-56%).

In male rats fed a diet containing 1.5% cholesterol and 5% of dried mushroom (Pleurotus ostreatus) a significantly reduced accumulation of cholesterol in serum (by 45%) and the liver (by 15%) was observed at the end of the 12th week of the experiment. The decrease in serum cholesterol level by more than 90% is a consequence of the decreased cholesterol concentration of very-low-density lipoproteins (VLDL) and of low-density lipoproteins. Consumption of P. ostreatus reduces the total VLDL entry into the circulation by 19% and accelerates (by 49%) fractional turnover rate of VLDL.

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