Abstract: This work aimed to investigate the formation mechanism of gelatin-sodium alginate complex (GEL-AG) at room temperature. The effects of GEL-to-AG ratio (m/m) and pH on the electrostatic interaction between the two compounds were studied by turbidity titration, zeta potential measurement, and methylene blue spectrophotometry. Isothermal titration calorimetry (ITC) was employed to elucidate the thermodynamic behavior of GEL-AG interaction. The results showed that the complex formation process was a spontaneous exothermic process driven by enthalpy through strong electrostatic interaction. The environmental pH influences the electrostatic interaction between GEL and AG through adjusting the net charge carried by them; insoluble complexes were formed at low pH and soluble complexes at high pH. Low concentration of NaCl (< 0.02 mol/L) could promote the combination between GEL and AG through electrostatic shielding, while high concentration of NaCl could inhibit the interaction. The electrostatic interaction between GEL and AG could be strengthened with increasing GEL-to-AG ratio or their respective total concentrations. At a GEL-to-AG ratio of 7:3, a stable complex suspension was obtained at a high pH, while pH in the range of 2.5–3.5 showed little influence on the properties of GEL-AG suspension. This study will be useful for the development of GEL-AG-based biomaterials and their application in the food and pharmaceutical fields.

Key words: gelatin; sodium alginate; isothermal titration calorimetry; electrostatic complex; turbidity