Cross-linking of sodium carbonate-soluble pectins from apple by zinc ions.

Sodium carbonate-soluble pectin fraction forms a self-organized network on mica and may have the potential ability to bind zinc ions. The aim of this research was to characterize the interaction of zinc ions with this fraction extracted from apples using rheological measurements and FT-IR study. The addition of zinc ions (10 and 20 mM of ZnSO4·7H2O) to 5% pectin water solution caused a significant increase in viscosity, which may be connected with the formation of a pectin network. Moreover, the addition of zinc ions resulted in an almost 1.5-fold decrease in the flow behaviour index and a 5-fold increase in the consistency index. FT-IR studies showed a decrease in the intensity of the bands connected with νas and νs(COO-) and γ(COH)ring as a result of the presence of zinc ions. Therefore, it may be supposed that these ions interact with the carboxylate and hydroxyl groups of galacturonic acid units.