Structural characteristics of gels formed by mixtures of carrageenan and mucilage gum from Opuntia ficus indica

Sol–gel and gel–sol transitions of mixtures formed by mucilage gum from Opuntia ficus indica and either κ-carrageenan or ι-carrageenan were studied using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). A total polymer concentration of 2% (w/w), a mucilage concentration in the interval between 0 and 80% (w/w), and KCl or CaCl2 concentrations of 12 or 60 mM, were used. Results from DSC showed that gelation was independent of the presence of mucilage gum in the mixtures. SEM results showed the non-gelling characteristic of mucilage gum from O. ficus indica. However, when mixed with κ-carrageenan a synergistic effect was observed only at the 80/20 κ-carrageenan/mucilage gum ratio. The DSC and SEM results indicated that the mucilage gum gets adsorbed onto the i-carrageenan structure in an interaction controlled by electrostatic charges. Regarding the i-carradeenan/mucilage mixtures no clear interaction at structural level was observed.