A Chemical Basis for Sour Taste Perception in Aqueous Solutions and Fresh Pack Dill Pickles.

Abstract

Sour taste is related to pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity simply by knowing the pH and the type and amount of acids present. The main objective of this study was to investigate the roles of protonated organic acid species and hydrogen ions in evoking sour taste perception. In order to test whether the intensity of sour taste was a linear function of the molar concentration of protonated organic acid species plus the molar concentration of hydrogen ions, pH of solutions was adjusted with sodium hydroxide resulting in other uncontrolled variables, such as organic anions and sodium ions. A secondary objective was to investigate the roles organic anions and sodium ions in suppressing sour taste intensity of acid solutions. Sour taste intensity and other sensory attributes were measured using the Spectrum MethodTM. The distribution of organic acid species was calculated using pHToolsTM, a modeling program implemented in MATLABTM. Mixtures of three acids, chosen from a group of eight organic acids, were used for testing the effect of protonated organic acid species, and hydrochloric acid was used for testing the effect of hydrogen ions. The effect of organic anions and sodium ions in suppressing sour taste intensity were tested at constant concentrations of protonated acid species and hydrogen ions. The effect of sodium ions was further investigated by adding NaCl to acid solutions in the absence of organic anion species. Sour taste increased linearly with hydrogen ion concentration (R2= 0.995), as well as with the molar concentration of protonated organic acid species at pH 3.5 (R2= 0.949), 4.0 (R2= 0.952), and 4.5 (R2= 0.975). Type of acid was not a determinant factor for sour taste intensity after adjusting for the effects of protonated organic acid species and hydrogen ion concentration. Protonated organic acid species and hydrogen ions were shown to be additive factors and produce approximately the same sour taste response on a molar basis. Furthermore, sour taste intensity was linearly related to the total concentration of protonated organic acid species in fresh pack dill pickles at pH 3.5 and 4.0 (R2= 0.999, 0.999, respectively). Suppression of sour taste in pH adjusted solutions was shown to be only partially explained by sodium ions and organic anions, although both seem to have an effect. This study reveals a simple chemical basis for the sour taste of organic acids and may allow for better control of flavor in the formulation of acidified foods.