According to the speculation, all the phenomena mentioned
above can be reasonably illustrated. For example, a sodium acetate
solution without adjusted pH had no sour taste, as there were no
undissociated hydrogen ions (pH 7.1) and the concentration of free
hydrogen ions was less than its sour taste threshold. In terms of the
three sodium acetate solutions at pH 4.0, although the concentration
of free hydrogen ions was below the sour taste threshold of
hydrogen ions, they all had an obvious sour taste, as there existed
protonated acetic acid species which contained undissociated
hydrogen ions. The total concentrations of all hydrogen ion species
in 50, 100, and 150 mg/l sodium acetate solutions were 0.65, 1.3
and 2.0 mM, respectively which are higher than the sour taste
threshold of hydrogen ions.