Effects of casein, ovalbumin, and dextran on the astringency of tea polyphenols determined by quartz crystal microbalance with dissipation.

Tea polyphenols (TPPs) can bind with proteins and peptides through hydrophobic interaction and hydrogen bonding. Casein, ovalbumin, and dextran were used to investigate their influence on the interactions between TPP and gelatin and, therefore, to investigate their influence on TPP taste. Casein-g-dextran (CgD) and ovalbumin-g-dextran (OgD) grafting conjugates were prepared through the Maillard reaction. Dispersible CgD/OgD-TPP complexes formed in acidic pH solution even after a heating process. At the same weight ratio of protein to TPP, about 20-30% of TPP was bound to the proteins. TPP affinity for dextran is much lower. Gelatin, a model of the salivary proteins in buccal cavity, was immobilized on quartz crystal sensor surface through covalent bond. By use of a quartz crystal microbalance with dissipation, we found that the complexation of TPP with gelatin causes a dehydration and collapse of the gelatin layer on the sensor surface that is similar to the sensation of dryness and constriction on oral membranes caused by polyphenols. The complexation between TPP and casein/ovalbumin/dextran can decrease the interaction between TPP and gelatin by decreasing the free TPP molecules and shielding gelatin surface from TPP. Casein has stronger binding ability on the gelatin surface compared to ovalbumin and dextran, and therefore casein is more effective to decrease the sensation of astringency caused by TPP.