Use of transferrin and EPR to probe the in vitro digestive chemistry of iron

Abstract

The study of the chemistry of iron in food materials undergoing digestion can increase our knowledge of the basis of iron bioavailability. Apotransferrin has been used as a probe of iron reactivity following the in vitro enzymatic digestion of pinto beans at pH 3.0 and pH 5.0 in the presence and absence of additives such as ascorbic acid, citric acid, a combination of ascorbic and citric acids, phosvitin, tea, and orange juice. Electron paramagnetic resonance spectroscopy was used to monitor and quantitate the exchange reactions. The effects of additives were similar when either the digestive slurry or its supernatant was reacted with apotransferrin. Although citric acid caused a two-fold increase in the digestive solubilization of pinto bean iron when compared to control, the amount of iron donated to transferrin was similar. The addition of ascorbic acid did not increase digestive solubilization of iron, however the iron exchange to transferrin increased 1.6 times. A maximum reactivity of pinto bean iron was observed when orange juice or ascorbic plus citric acids were included in the digestion. A strong inhibitory effect of tea on iron reactivity was seen. The order of additives in terms of their enhancement of the reaction of pinto bean supernatant with apotransferrin is: ascorbic plus citric acids > orange juice > ascorbic acid > citric acid > control > phosvitin > tea. This order parallels that expected for the effect of the additives on human iron bioavailability.