A comprehensive study of the relation between structural and physical chemical properties of acacia gums

Previously, we fully investigated the chemical and structural characteristics of two acacia gum samples. Now, the gums' physical chemical properties were investigated using zeta potential, fluorescence spectroscopy, potentiometric titration, viscometry and SAXS, and correlated to the gums's structural and self-association particularities. Since acacia gums are widely used in many food products, our aim was to elucidate the origin of the Acacia mearnsii gum (GN) properties in comparison with a commercial Acacia gum (GA). Both gums are negatively charged polyelectrolytes, nevertheless, the uronic acids in GN are stronger in view of the pKa of the carboxyl groups are ∼10-25% lower than in GA. Also, the acid dissociation constant (pKa) for both gums, can be related to the gums aggregation behavior. The pKa variability is more pronounced at lower gum concentrations and an inflexion point is noted close to the critical adsorption concentration. GN presents a more pronounced self-association behavior and a higher intrinsic viscosity (0.23 dL g−1vs 0.13 dL g−1), indicating a less compact structure. The SAXS scattering profile of GA revealed two size levels, consistent with a thin ellipsoid morphology with 2.0 nm (thickness) and 12.0 nm (radius). GN, though, presented just one broad bulge, suggesting a higher dispersity level. It was demonstrated that specific variations in the gums chemical structure reflect directly on their self-assembly feature which, in turn, plays an important role on the gums intrinsic physical chemistry properties, whatever the probed length scale.