Complexation between sodium caseinate and gallic acid: Effects on foam properties and interfacial properties of foam

The impact of gallic acid (GA) treatment on the adsorption behavior at the air/water interface and foam properties of sodium caseinate (SC) was investigated. The surface hydrophobicity and negative charge of SC were significantly decreased in bulk solution after interacting with GA. The combination between SC and GA was further confirmed by Fourier transform infrared spectrometer. Compared with SC, the foam stabilized by SC/GA complex (mass ratio of 1:1) showed excellent long-term stability. Moreover, the studies of air/water interfacial behavior demonstrated that the combination slightly decreased the interfacial activity of SC, but considerably increased its interfacial viscoelasticity, suggesting more stable of the air/water interface stabilized by SC/GA complex. Finally, the result of Lissajous plots analysis shows that the increase of GA content lead to the strain hardening occurs in the interface during compression and extension. This also proves that the addition of GA could improve the foam stability of the system.