, Volume 219, Issue 4, pp 409-415
Date: 27 Jul 2004

In vitro analysis of binding capacities of calcium to phytic acid in different food samples

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Abstract

The present work was performed to study the role which plays phytic acid in calcium binding, and to determine the calcium binding capacities in different foods, using in vitro extractions. Different food samples (soybeans, oats, chickpea, rice flour, and corn semolina) were extracted for 4 h at 37 °C using artificial simulated gastrointestinal juice (pepsin) at pH=2. The total calcium and phytic acid concentrations were determined by AAS and capillary electrophoresis, respectively, at pH=2 and pH=8 after neutralisation with a sodium hydroxide solution (3 M). Having determined the binding capacities of calcium in each food, we then use these results to estimate the fraction of calcium available for resorption during the process of digestion, when food moves from the acid pH of the stomach to the alkaline milieu of the intestines. The results obtained for the foods analysed show that the capacity of calcium to bind to phytic acid exhibits a clear pH dependence. The calculated calcium binding capacities, or the molar ratio of calcium to phytic acid in the in vitro extracted foods, varies from 3 mol calcium per mol phytic acid for soybean, chickpea and oats, to 2 mol calcium per mol phytic acid for rice, to1 mol calcium per mol phytic acid in corn semolina. Calcium may bind to one or more of the phosphate groups of phytic acid. Previous studies have demonstrated that phytic acid has the ability to bind minerals, proteins, and starch, and have then considered it as an inhibitor to the bioavailability of minerals and trace elements.