How to predict taste reactions?
Harry T. Lawless

Example: how much sourness would you like from an acidulant?
Problem: we have two acids to pick from.

1. First approach:
   Weight may predict sourness.
   The more we add, the greater the sour response.

   HOWEVER: acids have different molecular weights, and therefore at the same concentration weight-per-volume, will elicit different sourness responses, one acid having more protons per unit volume to donate.

2. Second approach:
   Molarity may predict sourness.
   The more molecules per unit volume, the greater the sourness response.

   HOWEVER: acids have different degrees of dissociation, and therefore at the same molarity, will have different concentrations of free protons and therefore different sourness impact.

3. Third approach:
   pH may predict sourness.
   The more free protons in solution, the greater the sourness response.

   HOWEVER, the oral tissues and salivary milieu are also reactive, and titrate protons off anions in equilibria. Therefore, not all acids are equally sour at equal pH.

4. Fourth approach:
   Titratable acidity may predict sourness. The concentration of available protons, down to a level at which the tissues may remove them is important. Titratable acidity to a pH of about 4 is a good predictor of sourness. However, there are still residual differences in sourness at equal titratable acidity.

5. Other potential factors:
   electrostatic interactions, e.g. from anion binding near sour (H⁺) receptors.
   taste properties of the anions themselves.