Cereal Chem 59:310 - 317.  |  VIEW ARTICLE
Cereal Complexes: Binding of Zinc by Bran and Components of Bran.

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

Binding of zinc ions in nonbuffered aqueous media by food-grade white wheat bran, by components of bran, and by substances normally found in gastrointestinal fluid was investigated in vitro at 37 C over the pH range 5-7. Analysis for uncomplexed Zn2+ was by means of the metal indicator tetramethylmurexide. Water-soluble components are responsible for about 39% of the total binding power of whole bran, and the principal soluble chelating agent is probably phytate. Bran that has been pretreated with dilute HCl at pH 1.6 contains an even greater concentration of soluble, zinc-binding substances. The combined contributions of cellulose, starch, hemicellulose, and pectin to the observed binding ability of bran are no greater than 10%. Each gram of bran contains about 0.27 mmol of zinc-binding sites, and each site is capable of chelating one zinc ion. Various gastrointestinal components were investigated for their possible role in binding Zn2+ in the human small intestine. On one hand, sugar, saliva, amino acids, albumin, and hydrogen carbonate ion at concentrations expected in the intestine have little effect on the concentration of free Zn2+. On the other hand, phosphate ion and mucin do cause significant zinc loss, and this loss might be high enough to influence bioavailability of zinc. The low solubility of zinc salts of certain bile acids may also be important biologically.