ANNE V. F. NIELSEN, ANNE S. MEYER
Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Soeltofts Plads 229, 2800 Kgs. Lyngby, Denmark

Abstract

Phytase enzymes present an alternative to iron supplements, because they have been shown to improve iron absorption by means of catalysing the degradation of a potent iron absorption inhibitor: phytic acid. Phytic acid is a hexaphosphate of inositol and is particularly prevalent in cereal grains, where it serves as a storage molecule for phosphorous. Phytic acid is also associated with minerals. The minerals are bound by chelation to the negatively charged phosphate groups in phytic acid. Phytases catalyse the dephosphorylation of phytic acid, thus releasing bound minerals to make them available for absorption. This article presents research on phytase catalysis in gastric conditions and considers potential benefits and drawbacks for using phytases as a food supplement.

INTRODUCTION

The World Health Organization has recently approved a phytase enzyme from the mould Aspergillus niger for use in foods (1). Several studies have demonstrated the efficacy of phytase enzymes for improving iron absorption from phytate-rich meals (Figure 1) (2–12). The objective of this study is to assess whether phytase catalysis in the gastric ventricle post ingestion may be practically possible and nutritionally useful.
Phytases (myo-inositol (1, 2, 3, 4, 5, 6) hexakisphosphate phosphohydrolase; EC 3.1.3.8) catalyse dephosphorylation of phytic acid (myo-inositol (1, 2, 3, 4, 5, 6)-hexakisphosphoric acid). Phytic acid is the major phosphorous storage compound in seeds and kernels and may constitute up to ~1.5 % of the kernels by weight (13). The phosphate groups of phytic acid are negatively charged at physiological pH values, thus making phytic acid a strong chelator of positively charged ions, notably minerals such as iron (Fe3+) and zinc (Zn2+) (13, 14). This chelation causes low bioavailability of minerals from phytate-rich foods, notably cereals. For iron, the bioavailability in typical cereals is as low as 2-3 % (15) ...