pH Influence on the stability of foams with protein–polysaccharide complexes at their interfaces

Food foams such as marshmallow, Chantilly and mousses have behavior and stability directly connected with their microstructure, bubble size distribution and interfacial properties. A high interfacial tension inherent to air/liquid foams interfaces affects its stability, and thus it has a direct impact on processing, storage and product handling. In this work, the interactions of egg albumin with various types of polysaccharides were investigated by drop tensiometry, interfacial rheology and foam stability. The progressive addition of egg albumin and polysaccharide in water induced a drop of the air–water surface tension which was dependent on the pH and polysaccharide type. At pH 4, that is below the isoeletric point of egg albumen (pI = 4.5) the surface tension was decreased from 70 mN/m to 42 mN/m by the presence of the protein, and from 70 mN/m to 43 mN/m, 40 mN/m and 38 mN/m by subsequent addition of xanthan, guar gum and κ-carrageenan, respectively. At pH 7.5 the surface tension was decreased from 70 mN/m to 43 mN/m by the simultaneous presence of the protein and κ-carrageenan. However, a higher surface tension of 48 and 50 mN/m was found when xanthan and guar gum were added, respectively, when compared with carrageenan addition. The main role on the stabilization of protein–polysaccharide stabilized interfaces was identified on the elasticity of the interface. Foam stability experiments confirmed that egg-albumin/κ-carrageenan at pH below the protein isoeletric point are the most efficient systems to stabilize air/water interfaces. These results clearly indicate that protein–polysaccharide coacervation at the air/water interface is an efficient process to increase foam stability.