Degradation of pectin in the caecum contributes to bioavailability of iron in rats

Abstract

The present study was designed to investigate the effect of pectin on Fe bioavailability in ileorectomised rats or caecectomised rats. In Expt 1, rats were divided into the following two groups: ileorectomised rats fed a fibre-free diet (FF diet) and ileorectomised rats fed a FF diet supplemented with 5 % (w/w) pectin (pectin diet). Apparent Fe absorption in ileorectomised rats fed the pectin diet was significantly lower compared with ileorectomised rats fed the FF diet. In Expt 2, caecectomised rats and sham-operated rats were given one of the following diets for 3 weeks: diet containing ferrous iron (FeII diet), diet containing pectin at 50 g/kg diet (pectin diet) and diet containing a mixture of FeII and product prepared by the enzymatic degradation of pectin (FeII–OGA diet), which were presumed to be oligomers of galacturonic acid. The Fe content of these diets was 7·6, 8·1 and 7·7 mg/kg diet, respectively. The bioavailability of Fe in rats fed the FeII diet was not affected by caecectomy. In contrast, in rats fed the pectin diet, where Fe bound to pectin was the only Fe source, Hb gain and Hb regeneration efficiency were significantly decreased by caecectomy. The bioavailability of Fe from the FeII–OGA complex was not affected by caecectomy. These results suggest that Fe in pectin might be released by microbial degradation and subsequently made available for absorption in the large intestine, although pectin might decrease Fe absorption in the small intestine.