In vitro binding of calcium, iron and zinc by non-starch polysaccharides

The in vitro binding capacity of eight non-starch polysaccharides (agar. Ic -carrageenan, gum xanthan. gum arabic, gum karaya, gum tragacanth, pectin a nd gum guar) was measured by equilibrium dialysis in neutral and acidic (0. 1M HCl) solutions in the presence of divalent cations (Ca2+, Zn2+). No sign ificant binding was observed in acidic conditions while, in neutral solutio ns, the extent of binding was correlated (P < 0.1) to the cation-exchange c apacity of the polysaccharides. It is apparent that the interactions are es sentially electrostatic in nature, due to the presence of ionised carboxyl (uronic:pyruvic acids) acid sulphated groups, in polyanionic polysaccharide s. By contrast, significant binding occurs with Fe3+ in acidic conditions, presumably due to complexation (chelation). These data provide a clear insi ght into how non-starch polysaccharides interact with minerals and the pote ntial nutritional consequence in terms of bioavailability. (C) 2001 Elsevie r Science Ltd. All rights reserved.