Cereal Chem 59:302 - 309.  |  VIEW ARTICLE
Cereal Complexes: Binding of Calcium by Bran and Components of Bran.

J. A. Rendleman. Copyright 1982 by the American Association of Cereal Chemists, Inc. 

Binding of calcium ions in aqueous media by food-grade white wheat bran, by components of bran, and by constituents of gastrointestinal fluid was studied in vitro at 37 C over the physiological pH range of 5-8. Analysis for free, uncomplexed Ca2+ was by means of the metal indicator tetramethylmurexide. No buffers wer used. Water-soluble components are responsible for more than half of the binding ability of bran, and the principal soluble chelating agent is phytate. Cellulose, starch, hemicellulose, and pectin (degree of esterification, 61%) have little affinity for Ca2+ at neutral pH and, therefore, as bran components, make no important contribution to calcium binding. Affinity of protein for calcium is also very low. At concentrations approximating those found in the human intestine, constituents of gartrointestinal fluid (ie, saliva, sugar, albumin, mucin, amino acids, phosphate ion, hydrogen carbonate ion, and bile acids) bind Ca2+ only very weakly. Extent of binding by these constituents was too small to measure accurately.