British Journal of Nutrition

Mineral Metabolism

A continuous in vitro method for estimation of the bioavailability of minerals and trace elements in foods: application to breads varying in phytic acid content

Mechteldis G. E. Woltersa1, Hendrika A. W. Schreudera1, Grietje Van Den Heuvela1, Henk J. Van Lonkhuijsena1, Ruud J. J. Hermusa2 and Alfons G. J. Voragena3

a1 TNO Biotechnology and Chemistry Institute, Department of Biochemistry and Physical Chemistry, PO Box 360, 3700 AJ Zeist, The Netherlands

a2 TNO Toxicology and Nutrition Institute, PO Box 360, 3700 AJ Zeist, The Netherlands

a3 Wageningen Agricultural University, Department of Food Science, Biotechnion, PO Box 8129, 6700 E V Wageningen, The Netherlands

Abstract

A continuous in vitro method for the estimation of the bioavailability of minerals and trace elements is presented. This in vitro method is believed to be more representative of in vivo physiological conditions than in vitro methods based on equilibrium dialysis, because dialysable components are continuously removed from the pancreatic digestion mixture. The continuous in vitro method is compared with the equilibrium in vitro method with respect to the dialysability of Ca, Mg, Fe, Cu and Zn from eight different types of bread (varying in phytic acid content). The results show a pronounced effect of continuous removal of dialysable components from the pancreatic digestion mixture on the dialysability of minerals and trace elements. Furthermore, removal of dialysable components influences the effect of phytic acid on the bioavailability of minerals and trace elements. For these two reasons the importance of removal of dialysable components in vitro for the estimation of bioavailahility in vivo needs further investigation. The bioavailability of minerals and trace elements from bread samples is not related to the phytic acid content only. Therefore, the effect of phytic acid on the bioavailability of minerals and trace elements cannot be studied separately from the effects of other components on bioavailability.

(Received February 05 1992)

(Accepted June 04 1992)

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