Binding of Na+ ions to proteins: Effect on taste perception

This study investigated the relationship between the ionic binding of sodium and salty perception in protein matrices. Protein type (i.e. gelatin, milk protein and soy protein), protein concentration and pH were varied to obtain matrices with distinct compositions and rheological properties. 23Na NMR spectroscopy was used to determine the ratio of sodium ions bound to proteins and the mobility of sodium ions. The results showed that protein type, concentration and pH affected the rheological properties of the protein matrices, the ionic binding of sodium ions and taste intensity. As the protein concentration increased, the mobility of sodium ions decreased and the ratio of bound sodium ions increased. Gelatin matrices displayed the greatest mobility of total sodium ions and the smallest amount of bound sodium. Soy protein had a larger amount of bound sodium than milk protein. Lowering the pH of milk protein matrices tended to decrease the ratio of bound sodium and increase sodium mobility. We suggest that sodium ionic binding is related to the presence of negatively charged groups in proteins. Although changes in matrix composition modified sodium ionic interactions, taste perception was mainly affected by the rheological properties of the protein matrices. As the values of fracture stress or viscosity increased, firmness intensity increased and saltiness intensity decreased. The observed effects of texture on taste could be explained by cross-modal texture-taste interactions and by differences in the oral breakdown behavior of protein matrices.