Surface behavior and bulk properties of aqueous chitosan and type-B gelatin solutions for effective emulsion formulation

•Chitosan-type B Gelatin coacervation occurs through electrostatic interaction.•The coacervate formation was influenced by pH and concentration ratios of CH and GB.•Chitosan (CH) was found more surface active than type-B gelatin (GB).•CH and CH-GB blend were found more efficient to stabilize emulsion than GB. The behavior of aqueous chitosan (CH), type-B gelatin (GB) and CH-GB coacervate was studied on oil-in-water emulsion formulation at various pH and concentration ratio. The coacervate was formed by phase separation at ratios CH:GB, 1:10 to 1:1 with total biopolymer concentrations of 0.55%-1.0% (w/v) at pH 4.0-5.5. Soluble complexes were formed below pH 5.0 and coacervate formation was confirmed at pH 5.0 and above by zeta potential and UV-spectroscopy measurements. The coacervate formation was found maximum at the CH-GB ratios of 1:10 and 1:5 at pH 5.5. Formulated emulsions (>10μm droplets) using 1% (w/v) chitosan and GB were found stable (+52.5mv and creaming index 86%) and unstable respectively. Emulsion stabilized by mixed CH:GB 1:5 (3%w/v) had no creaming effect. The instability was attributed to the lower surface activity (K=5.0Lg−1) of pure GB compared to CH (K=14.3Lg−1). The formulation and methods can successfully tune the stability of the emulsions.