Phytate, zinc, and calcium contents of 30 East African foods and their calculated phytate:Zn, Ca:phytate, and [Ca][phytate]/[Zn] molar ratios

Abstract

Representative samples of 30 staple Malawian foods, raw and prepared “as eaten,” were analyzed for phytate using an anion-exchange method, and for calcium and zinc by flame atomic absorption spectrophotometry. Phytic acid contents expressed on a fresh weight (FW) basis ranged from 211–1089 mg/100 g for cereals and 166–1297 mg/100 g for legumes, to 4–97 mg/100 g for leaves, 10–59 mg/100 g for roots, and 11–25 mg/100 g for fruits. In general, leaves had the highest calcium content (81–514 mg/100 g FW), followed by kidney beans (90 mg/100 g FW), and dry pigeon peas (112 mg/100 g FW). The calcium content of other foods analyzed was relatively low. The zinc content of wild blight, cassava leaves, and okra leaves was comparable to that for the less refined cereals and legumes (i.e., > 1.0 mg/100 g FW), but higher than that of highly refined cereals, pumpkin leaves, chinese cabbage, and other foods analysed (i.e., < 1.0 mg/100 g FW). Cooking had no effect on the phytate content of cereals, but milling and fermentation reduced both the phytate and zinc contents of maize flour. The phytate:Zn molar ratios calculated for all cereals and most legumes analyzed were greater than 20:1. Corresponding Ca:phytate molar ratios were low. Fruits, except for mangoes, vegetables, and roots, had low phytate: Zn molar ratios, but their Ca:phytate and [Ca][phytate]/[Zn] molar ratios were high. Mangoes had high phytate:Zn, Ca:phytate, and [Ca][phytate]/[Zn] molar ratios. These analytical results suggest that the bioavailability of zinc in the Malawian diet is probably low, due to the high phytic acid content of the staple foods.