In vitro bioavailability of calcium and iron from selected green leafy vegetables

Abstract

The objective of the present investigation was to analyze the relative influence of oxalic acid, phytic acid, tannin and dietary fiber on in vitro availability of iron and calcium from green leafy vegetables (GLV). Thirteen GLV were selected and analyzed for iron, calcium, oxalic acid, phytic acid, tannin and dietary fiber contents using standard methods. The bioavailability of calcium and iron in the GLV was estimated by equilibrium dialysis. Oxalic acid content was less than 1 g kg-1 in four greens and ranged between 1.22 to 11.98 g kg-1 in the remaining. Dietary fiber ranged from 19.5 to 113.7 g kg-1. Tannin content ranged between 0.6138 and 2.1159 g kg-1 with the exception of two GLV that had 0.1332 and 14.8619 g kg-1. Four GLV were found to have approximately 40% bioavailable iron, while the others were in the range of 6-30%. In vitro available calcium was less than or equal to 25% in eight GLV and between 34% and 52% in five GLV. Multiple regression analysis revealed that these factors together accounted for 53% (r2 = 0.53) and 45% (r2 = 0.45) inhibition of iron and calcium absorption, respectively. These findings infer that calcium and iron availability is influenced by the constituents present in the GLV. © 2006 Society of Chemical Industry.