Comparative analysis of influence of promoters and inhibitors on in vitro available iron using two methods

The investigation was undertaken with the objective of comparing two in vitro techniques, measuring dialyzable iron (method A) and measuring ionizable iron (method B), for iron bioavailability in a model system. The effect of the time of introduction of the additives on the available iron was also determined. FeSO4 solution was used as the reference source of iron, to which a series of enhancers (ascorbic acid, citric acid, maleic acid and tartaric acid) and inhibitors (tannic acid, calcium oxalate, oxalic acid, calcium carbonate and sodium phytate) were added individually at various concentrations, and available iron was estimated. From FeSO4 solution, 0.1% (method A) and 3.9% (method B) of iron was available. The addition of ascorbic acid, citric acid and tartaric acid increased this by 33-50%, 28-57% and 23-90%, respectively, for method A and by 15-89%, 24-78% and 24-93% for method B. Tannic acid, sodium phytate and calcium oxalate exhibited an inhibitory effect irrespective of the concentrations, while oxalic acid and calcium carbonate exhibited a dose-dependent inhibitory pattern. The iron availability analyzed by both methods showed a positive correlation with seven out of nine additives. An inverse relation was seen between the inhibitory effect of calcium carbonate and calcium oxalate and their time of introduction into the system. The overall observations showed that although absolute values varied widely, a positive correlation existed between the methods.