Effects of Epigallocatechin Gallate on β-Casein Adsorption at the Air/Water Interface

Protein adsorption at the air/water interface is of first interest in foam stabilization and has been much studied. Though interactions between polyphenols and proteins in solution have been demonstrated, their effects on protein adsorption properties are totally unknown. The aim of this work is to study the effect of epigallocatechin gallate on β-casein adsorption. Protein adsorption from a polyphenol−protein solution was monitored by tensiometry and ellipsometry. The adsorption layer structure was measured by spectroscopic ellipsometry, and viscoelastic properties were monitored by an oscillating bubble method. Adsorption kinetics shows that protein adsorption is slowed by the polyphenol. While polyphenol adsorption from pure polyphenol solution is not observed, polyphenol adsorption from the mixture is observed. It seems that protein surface concentration is increased when polyphenol bulk concentration is smaller than 60 mg/L and that protein surface concentration is decreased when polyphenol bulk concentration is larger than 60 mg/L. Moreover, the elastic modulus of the layer increases after the formation of the layer. From these results, it can be concluded that β-casein adsorption properties are greatly modified by the polyphenol. However, the mechanisms involved remain to be understood.