Thermodynamic parameters of gelatin-pectin complex coacervation

Investigating the thermodynamic parameters in the formation process of protein-polysaccharide complex coacervates is very important for understanding the binding mechanism of the two biopolymers and regulating food properties by using complex coacervates. Herein, the influence of pH, salt ion strength and temperature on the thermodynamic parameters of gelatin (G)-pectin (P) complex coacervation were explored by using isothermal titration calorimetry (ITC), supplemented by dynamic light scattering and turbidity measurement. The results showed that G and P could form complex coacervates mainly through electrostatic bonding with different strength in the pH2.0–10.0. The complex coacervation process of G and P at pH 3.5 was spontaneous driven by entropy, while the binding at pH 8.5 and 9.5 was enthalpy driven. In addition, the electrostatic binding of G/P at pH 3.5 changed into an enthalpy driven process with the increase of salt ion concentration to 100 mM. Finally, the binding constant between G and P decreased with the increase of temperature from 25 °C to 45 °C, as well as positive ΔH and ΔS and negative ΔG, suggesting that the binding also involves hydrogen bonding and hydrophobic interaction. These findings could provide in-depth understanding of the application of G/P complex coacervates in the design of food structure.