4. Conclusions
Through this research, it was concluded that hydrogen ions are
the fundamental substance producing a sour taste. Hydrogen ions
have two forms: one is free hydrogen ion species, and the other is
the undissociated hydrogen species, which is bound to the anionic
acid species. The intensity of sour taste is related to the total concentration
of free and undissociated hydrogen ions. The threshold
of sour taste of pure free hydrogen was determined to be
0.575 mM, which corresponds to pH 3.24. The anionic acid species
has no sour taste, but can affect the intensity of sour taste of the
hydrogen ion which is bound to it. The effects of anionic acid species
on the intensity of the sour taste are determined by structure.
The effects will be similar if the structures of the anionic acid species
are similar. The hydroxyl or conjugated groups in the anionic
acid species can intensify a sour taste, so the thresholds of organic
acids which contain these groups will be lowered.