Effect of crosslinking with Ca⁺⁺ and Zn⁺⁺ in the formation of gellan gum gels

Abstract

This study involves an investigation of the effects of crosslinking of gellan gum (GG) with Ca⁺⁺ or Zn++ on the physical properties of GG gels. GG gels crosslinked with different concentrations of Ca⁺⁺ or Zn⁺⁺ were prepared and parameters such as % water holding capacity and penetration thickness were investigated as measures of the extent of interaction of Ca⁺⁺ or Zn⁺⁺ with GG molecules. Data generated from the above studies revealed that Zn⁺⁺ interacted with the GG molecules to a greater extent than Ca++ . In order to further strengthen our finding, we have prepared Zn⁺⁺ crosslinked and Ca⁺⁺ crosslinked floating GG beads respectively by ionotropic gelation in the presence of a gas-generating agent (NaHCO3 ) and compared their physico-chemical properties such as density, drug entrapment efficiency and release in 0.1 M HCl (pH 1.2) using metronidazole (MTZ) as a model drug. Experimental data suggested that Zn⁺⁺ crosslinked floating GG beads were denser and less buoyant than Ca⁺⁺ crosslinked floating beads but capable of significantly (p < 0.05) improving MTZ entrapment efficiency and sustaining the MTZ release in 0.1 M HCl (pH 1.2) compared to Ca++ crosslinked floating beads. The difference in observed behavior may be attributed to differences in specificity, soft and hard character, enthalpies of hydration and ionization potentials of Ca⁺⁺ and Zn⁺⁺ .