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Dietary Aspergillus niger Phytase Increases Iron Absorption in Humans^1,2,

Ann-Sofie Sandberg^*,3, Lena Rossander Hulthén and Maria Türk^*

^* Chalmers University of Technology, Department of Food Science, S-402 29 Göteborg Sahlgren's Hospital, Department of Clinical Nutrition, Göteborg University, S-413 45 Göteborg, Sweden

Phytate is an inhibitor of iron absorption that can be removed before the intestinal site of absorption by microbial phytase, thereby increasing iron absorption from a meal. The effects of two kinds of dietary phytase, cereal phytase and microbial phytase from Aspergillus niger, on iron absorption were investigated. Iron absorption was measured from single meals containing white wheat rolls supplemented with wheat bran with or without phytase activity (expt. 1) and phytase-deactivated wheat bran with or without addition of microbial phytase from A. niger (expt. 2). Each experiment had 10 subjects and two different radio iron tracers: ⁵⁵Fe and ⁵⁹Fe were used for comparison of the absorption from the test meals in each experiment. No differences in iron absorption were found between meals containing wheat bran with or without phytase activity. Addition of microbial phytase to the meal containing phytase-deactivated wheat bran increased iron absorption from 14.3 ± 2.6% to 26.1 ± 3.8% (P < 0.0001). Two pH optima, one at pH 2.0 and one at pH 6.0, were found for A. niger phytase at 37°C, but activity occurred at all pH values between 1.0 and 7.5. The results suggest that effective and complete degradation of phytate occurred in the stomach when A. niger phytase was given with the meal. This may be explained by high activity of microbial phytase at physiological pH conditions of the stomach, whereas wheat phytase has a different pH optimum.

KEY WORDS: • phytase • phytate • iron absorption • humans

¹ Supported by grants from the Swedish Council for Forestry and Agricultural Research 50.0474/91, 711.0656/91.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom reprint requests should be addressed.

Manuscript received 16 June 1995. Revision accepted 24 October 1995.