In order to verify whether the protonated acid species makes a
contribution to sour taste, different concentrations of sodium acetate
solutions were prepared and adjusted to pH 4.0 using
hydrochloric acid. The intensity of sour taste of these solutions
was then scored (Fig. 2). Fig. 2 shows that the intensity of sour
taste for these sodium acetate solutions increased with an increase
in concentration of protonated acetic acid species. In the acetate
solutions, the concentrations of hydrogen ions were identical, but
the concentrations of protonated acetic acid species were different.
Thus the results suggested that the protonated acetic acid species
cannot only produce a sour taste, but the higher its concentration,
the stronger is the sour taste.