Controlling microstructure and physical properties of biopolymer hydrogel particles through modulation of electrostatic interactions

Foods contain varying amounts of salts and acids, which alters the electrostatic interactions between biopolymer molecules. This study therefore examined the influence of NaCl content (0-400 mM) and pH (3-8) on the physical properties of hydrogel particles fabricated by mixing sodium caseinate (1.5%) and pectin (1.5%). The hydrogel particles were assembled using a biopolymer phase separation approach that involved both segregation (thermodynamic incompatibility) and aggregation (complex coacervation) mechanisms. The addition of NaCl increased hydrogel particle size and altered the shape from spherical to rod-like, which was attributed to the influence of salt on the electrostatic attraction between biopolymers. There was a reduction in the lightness and increase in the shear viscosity of the hydrogel particle suspensions with NaCl addition, which was attributed to changes in particle dimensions and morphology. Solution pH also altered particle size and shape, and therefore the lightness and viscosity of the suspensions. In particular, the lightness of the suspensions was greater at pH 3-5, than at higher pH values. This study highlighted the significant effects of salt and pH on the properties of hydrogel particles. This knowledge could be used to manipulate food formulations to achieve desirable physicochemical or sensory properties.