Relating ionisation of calcium chloride in saliva to bitterness perception.

Saliva plays a role in the perception of bitter, sour and salty tastes that are presumed to be derived from the concentration of free cations or anions ions dissolved in saliva. The role of ionisation of calcium in bitter taste was studied by determining binding in vitro mixture of saliva and protein solutions and in spit. In vitro, the addition of whey to calcium chloride solutions increased the calcium binding, pH and viscosity. The addition of saliva to these mixtures, the increased calcium binding and the induced small changes in viscosity and pH were thought not to contribute significantly to bitterness perception. Nonstimulated saliva, at pH 7.5, contained about 5 mM calcium, of which about one third was ionised. The bitter threshold of fully ionised calcium chloride in water varied between 1 and 15 mM among individuals. In spit, after tasting whey, ionised calcium was found to have increased at low, but decreased at high, calcium concentrations and varied 30% among individuals. Bitterness was related, on average, to the concentration of ionised calcium and not to the total concentration of calcium in spit. A general explicative model based on the composition of bulk saliva is discussed in relation to perception threshold and the likely importance of saliva from von Ebner's gland.