The interactions between the two negatively charged polysaccharides: Gum Arabic and alginate

Abstract Although a combined formulation of gum arabic and alginate is used for a variety of applications in pharmaceutical, food, and cosmetic industries, the origin of the interactions between these two polysaccharides has not yet been systematically studied or established. This study investigated the nature and strength of the possible interactions between gum arabic and alginate, using a variety of techniques: solid-state nuclear magnetic resonance spectroscopy (SS-NMR), infrared spectroscopy (FTIR), isothermal titration calorimetry (ITC), hydrophobic-interaction-chromatography (HIC), fluorescence spectroscopy, rheology, differential scanning calorimetry (DSC), and thermogravimetric (TG) analyses. The results showed that alginate interacts with gum arabic at pH 4, despite the net negative charge of each of them. Of the three main fractions of gum arabic (i.e., the arabinogalactan-peptide fraction containing 1 wt% protein, arabinogalactan protein containing 10 wt% protein, and glycoprotein containing 25–50 wt% protein), only the latter two fractions interact with alginate. The interaction intensity of glycoprotein with alginate was almost four times greater than the interaction intensity of arabinogalactan protein with alginate. We suggest the local positive charges in the proteinaceous content of gum arabic at pH 4 enables an electrostatic interaction between proteins in the second and the third fractions of gum arabic with negatively charged carboxylate groups in alginate. The gum arabic-alginate-mixture presented different thermal behavior, higher viscosity, and elastic modulus compared with the individual solutions of gum arabic or alginate at pH 4. The information obtained from this study will be beneficial for the rational design of biopolymers that give foods novel textural properties.