Foaming and surface properties of casein glycomacropeptide–gelatin mixtures as affected by their interactions in the aqueous phase

Gelatin is widely used in food industry for the stabilization of foam products. On the other hand, casein glycomacropeptide (CMP) is a bioactive peptide with high surface activity. The aim of this work was to study the interfacial and foaming properties of CMP–gelatin mixed systems at pH 6.5 and 3.5 and evaluate the relation of these properties with the interactions in the aqueous phase. The CMP:gelatin ratio in mixed systems was 0:100 (pure gelatin), 25:75, 50:50, 75:25 and 100:0 (pure CMP). Viscosity, particle size, ζ-potential, interfacial properties and foaming properties were determined. At both pH, gelatin solutions showed the highest viscosity, CMP the lowest and the mixed systems presented behaviour more similar than CMP. Particle size and ζ-potential determinations evidenced the formation of complexes between CMP and gelatin at both pH. CMP was more surface active than gelatin and dominated the rate of diffusion of the mixed systems to the air–water interface. A synergistic effect was observed on foamability and foam stability in mixed systems that could be explained by the formation of a complex between CMP and gelatin with outstanding capacity for foams formation and stabilization.