bran during passage through pig gastrointestinal tract: Comparison with model predictions

Dietary fibers may limit mineral bioavailability through ion-exchange processes. To critically test this hypothesis, it is necessary to know the extent of mineral binding under gastrointestinal conditions. This work describes the merits and limits of methods devised to determine the extent of ion binding by dietary fiber in vivo. Corn bran was employed as the dietary fiber source. Bran was fed to pigs, then retrieved along with digesta from various gastrointestinal locations. Corn bran cation content (Na-, K·, and Ca -) was determined by energy-dispersive X-ray spectroscopy (EDX). EDX-determined ion contents were partitioned into bound and free fractions based on a previously developed ion-exchange model, the estimated free (aqueous) concentrations of electrolytes in the digesta, and the aqueous solution content of hydrated corn bran. The model provided estimates of bound Na-, K -, lvlg"-, and Ca2 for upper gastrointestinal locations. Colon ion concentrations were too high to be used in the model. Sodium values determined by EDX were insufficiently precise to test the adequacy of the model. Values for K· and Ca2 content determined by EDX analysis agreed well with model predictions when the extent of corn bran hydration was known explicit!.v. Correlation between model and observed values was poorer when bran hydration extent was simply estimated. Model predictions based on measured ion concentrations in the digesta suggest that calcium associated with corn bran in jejunum and ileum segments was predominantly bound, while most K and Na· was free. It was concluded that corn bran can bind sufficient Ca2 in the upper gastrointestinal tract to impact Ca2 absorption to a small extent under certain dietary regimes.