Investigating the gelation behavior and mechanisms of Ficus awkeotsang Makino pectin under the influence of different cations.

This study explored the gelation behavior, gel properties, and mechanisms of Ficus awkeotsang Makino Pectin (JFSP) under monovalent (Li, Na, K, Rb, Cs) and divalent metal ions (Mg, Ca, Fe, Zn, Sr, Ba). At a polymer concentration of 0.3 % (w/v), stable gels formed with divalent ions at 1.8 × 10 mol/L and monovalent ions at 4.5 × 10 mol/L. The addition of metal ions increased the particle size of pectin dispersions, with divalent ions causing a larger increase (180.3 ± 0.3 and 202.2 ± 2.3 nm) compared to monovalent ions (170.2 ± 0.6 to 177.3 ± 0.2 nm). Also the metal ions neutralized negative charges on pectin molecules and transformed layered pectin gels into an ordered and porous network, as confirmed by scanning electron microscopy. Atomic force microscopy and small-angle X-ray scattering further confirmed a cross-linked structure with smaller inter-chain distance in Ca-treated gels (2.67 nm) compared to K-treated (2.95 nm) and control samples (3.65 nm). Microrheology indicated enhanced pectin interactions and network heterogeneity upon ion addition. Infrared spectroscopy showed intensified ionic carboxyl group vibrations, suggesting interactions between free carboxyl groups and cations, reducing electrostatic repulsion and promoting chain entanglement and cross-linking. Therefore, divalent ions, especially Ca, promoted gelation and improved gel hardness (20.15 ± 0.62 g), water holding capacity (98.86 ± 1.06 %), and stability (water loss rate of <10 %). These findings highlight the critical role of ion type and concentration in optimizing JFSP gel performance, with important implications for the development of JFSP-based functional foods.