Strong gelation capacity of a pectin-like polysaccharide in the presence of K ion.

In the present study, a pectin-like apple polysaccharide (AP) obtained by metal precipitation technique was demonstrated to show strong gelling capacity in the presence of K ion upon cooling. Increasing amount of K addition monotonically promoted the gelation of AP, as characterized by the increased gelation temperature (T), gel melting temperature (T) and the gel strength. Compared with K ion, Na was unable to induce AP gelation even at high ionic concentrations, but other monovalent cations (Rb, Cs) can induce the gelation as in the case of K addition. At room temperature, the minimum cationic concentration as required to induce AP gelation followed the order of K ≈ Cr (8 mM) > Rb (3.5 mM), indicating that cationic radius (Na < K < Rb < Cs) played a dominant role in inducing AP gelation, but other factors may also be involved. Finally, the gelation behavior of AP in the presence of K was explained as the suppressed intermolecular electrostatic repulsion between AP chains due to the strong electrostatic shielding effect of K, which led to the formation of a gel network mediated by intermolecular hydrogen bonding. This reported gelation property may allow AP to find application as a new gelling polysaccharide.