Interfacial Study of Class II Hydrophobin and Its Mixtures with Milk Proteins: Relationship to Bubble Stability

Class II hydrophobin (HFBII) is a very promising ingredient for improving food foam stability. Pure HFBII-stabilized bubbles exhibited exceptional stability to disproportionation (dissolution) but were not stable to bubble coalescence induced by a pressure drop. Bubbles stabilized by mixtures of HFBII + sodium caseinate (SC) or beta-lactoglobulin (BL) showed decreased shrinkage rates compared to pure SC or BL and improved the stability to pressure-drop-induced coalescence. Higher bubble stability was more closely correlated with higher surface shear viscosity than the surface dilatational elasticity of the mixed protein systems. Brewster angle microscopy observations and the high shear strength of adsorbed films, including HFBII, even in the presence of hydrophobic and hydrogen-bond-brealcing agents, confirm that intermolecular attractive cross-links are unlikely to be the origin of the high strength of HFBII films. Possibly the HFBII molecules form a tightly interlocking monolayer of Janus-like particles at the air-water interface.