Relating the variation of secondary structure of gelatin at fish oil-water interface to adsorption kinetics, dynamic interfacial tension and emulsion stability

The objectives of this study were to quantify the relationship between secondary structure of gelatin and its adsorption at the fish-oil/water interface and to quantify the implication of the adsorption on the dynamic interfacial tension (DST) and emulsion stability. The surface hydrophobicity of the gelatin solutions decreased when the pH increased from 4.0 to 6.0, while opposite tend was observed in the viscosity of the solution. The DST values decreased as the pH increased from 4.0 to 6.0, indicating that higher positive charges (measured trough zeta potential) in the gelatin solution tended to result in higher DST values. The adsorption kinetics of the gelatin solution was examined through the calculated diffusion coefficients (Des). The addition of acid promoted the random coil and beta-turn structures at the expense of alpha-helical structure. The addition of NaOH decreased the beta-turn and increased the a-helix and random coil. The decrease in the random coil and triple helix structures in the gelatin solution resulted into increased D-eff values. The highest diffusion coefficients, the highest emulsion stability and the lowest amount of random coil and triple helix structures were observed at pH = 4.8. The lowest amount of random coil and triple helix structures in the interfacial protein layer correlated with the highest stability of the emulsion (highest ESI value). The lower amount of random coil and triple helix structures allowed higher coverage of the oil-water interface by relatively highly ordered secondary structure of gelatin.