Citrus pectin, binding bile salts

Does Citrus Pectin Bind Bile Salts A possible mechanism by which dietary pectin may cause lowering of cholesterol levels in rats has been reported (1 9). In these in vitro studies, pectin was found to inhibit the transport of taurocholic acid from everted sacs of rat intestine. The absorption of labelled cholesterol was depressed by the addition of 5% pectin to the diet as evidenced by increased excretion of labelled cholesterol and diminished cholesterol deposition in the liver. It was concluded from these studies that pectin lowers cholesterol levels in cholesterol-fed rats primarily by binding bile salts and, consequently, by impairing cholesterol absorption. Results similar to those obtained with dietary pectin and described have also been reported for other non-nutritive substances such as guar gum, psyllium seed colloid and seruglucan (20). 

Recently the means by which pectin lowers cholesterol levels and even the validity of this effect have been questioned. Upon finding no bile salt binding capacity for soluble pectin, Baig and Cerda (76) proposed that pectin lowered serum cholesterol levels by forming insoluble complexes with the serum low density lipoproteins (LDL) which transport circulating cholesterol. Complexing of LDL by citrus pectin was observed in vitro, but the way in which pectin or some component thereof enters the blood stream to effect such binding in vivo has not been determined. 

Pfeffer et al. (82) have found that bile salt binding activity of commercial citrus pectins was lost if these products were dissolved, filtered, centrifuged, and reprecipitated before testing. Binding activity was concentrated in the residue pellet from centrifugation, which was found to be fine diatomaceous earth. This contaminant was probably introduced during filtration steps in processing and purification of pectin. The authors concluded that any hypocholesterolemic effect of commercial pectin was due solely to its diatomaceous earth contamination. 

Carrot fiber, prepared as an alcohol-acetone insoluble residue of cell wall material, binds deoxycholate and chenodeoxycholate under physiological conditions with the release of protons. Removal of calcium pectate from this material by extraction with ammonium oxalate reduces the capacity of carrot fiber to bind bile acids. Calcium carboxymethyl cellulose exhibits similar binding activity, whereas free carboxymethyl cellulose shows no binding. Calcium pectate prepared from citrus pectin and dissolved in water was found to bind bile acids under conditions used with carrot fiber. These results suggest that binding occurs through formation of salt linkage between calcium pectate in the cell wall residue and a bile acid. 

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