Development and characterization of gelatin and Persian gum composite edible films through complex coacervation

Composite films of Persian gum (PG) and gelatin (G) were prepared by complex coacervation approach at different mixing ratios (100:0, 75:25 and 50:50, respectively) and critical pH levels corresponding to the electrostatic interactions. First, PG, G, and their mixture solutions were characterized in terms of turbidity as a function of pH. The maximum interaction of biopolymers was observed at pH 4.18 and the corresponding composite film revealed a compact and homogeneous structure as a result of strong electrostatic interactions and hydrogen bondings within the film network, whereas PG films had rough and slightly irregular surfaces as observed in SEM micrographs. Moreover, composite films showed reduced water solubility and elongation at break and enhanced water vapor barrier properties and tensile strength. G concentration positively affected the lightness of films, while the reverse trend was observed for opacity. In the DSC thermograms of composite films, there was only one glass transition temperature which decreased gradually with an increase in the G content, indicating appropriate miscibility between biopolymers in the film matrix. In general, the most desirable composite regarding physical and mechanical characteristics was produced from the interaction of PG and G at a mass ratio of 50:50 and pH 4.18. •Persian gum and Gelatin are miscible at the molecular level.•The molecular interactions are produced by hydrogen bonds and electrostatic forces.•The molecular interactions hinder the formation of Persian gum network.•The thermal stability of composite films decreases with increasing gelatin content.