American Journal of Clinical Nutrition, Vol 34, 1392-1401, Copyright © 1981 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

The effect of chemical agents, beverages, and spinach on the in vitro solubilization of iron from cooked pinto beans

N Kojima, D Wallace and GW Bates

The solubilization of iron from cooked pinto beans was examined using an improved in vitro methodology. The iron content of the beans was found to exist in three populations: 1) that which is spontaneously soluble upon incubation; 2) that which can be mobilized by chelating or reducing agents; and 3) that which is more firmly bound to the insoluble bean residue. These fractions constitute approximately 25, 45, and 30%, respectively, of the bean iron content when using consecutive 30-min incubations at pH 2 and 6. Ascorbic acid is maximally effective in iron mobilization under acidic conditions and acts via iron reduction. Citric acid is maximally effective near pH 6. The combination of ascorbic acid and citric acid leads to the solubilization of 70% of the iron content of the beans. Orange juice also leads to maximal soluble iron, predominantly in the Fe2+ state. Tea severely decreases iron solubility in the system. Only 3% of the iron content of spinach is solubilized by 10 mM ascorbic acid. Whole spinach suspension and the insoluble spinach residue are able to remove iron from solution that was previously solubilized from beans.