Tea polyphenols association to caseinate-stabilized oil–water interfaces

Abstract

Tea Catechins associate with proline rich proteins such as caseins. In this work, the interactions between epigallocatechin-gallate (EGCG), one of the main tea catechins, and caseins at an oil water interface were studied. The association of EGCG with sodium caseinate was quantified by measuring the amount of EGCG adsorbed on the emulsion droplets. In addition, the viscoelastic properties of the protein and EGCG–protein layers formed at the interface were studied using drop tensiometry. Different concentrations of EGCG were added to a model emulsion to obtain final concentrations of 10% soybean oil, 0.5% sodium caseinate and 0–9 mg/mL EGCG. At concentrations < 2 mg/mL EGCG, more than 90% was adsorbed at the interface. At higher concentrations, below 5 mg/mL, about 70% of EGCG was adsorbed. The surface load reached about 1 mg/m2 at 9 mg/mL of EGCG. The dissociation constant for the complex formed, was estimated using schatchard plot, and was 3.7 × 10−5 M for less than 20 mol bound EGCG/protein. The interactions of EGCG with sodium caseinate did not affect the interfacial tension but increased the dilational modulus of the EGCG-protein layer at the interface. This study demonstrated that sodium caseinate emulsions could be employed as carriers for EGCG, and that the complexes formed at the interface are affecting the physico-chemical properties of the emulsions. The results are of significance in the development of dairy based beverages containing tea polyphenols.