Astringent subqualities in acids.

Astringency, astringent subqualities (drying, roughing and puckering) and sourness were compared among six acids: hydrochloric, lactic, citric, acetic, fumaric and malic acids. The attribute profiles of organic acids were similar to each other but different from hydrochloric acid, the only inorganic acid, which was the most astringent and the least sour. In a second experiment, two inorganic acids (hydrochloric and phosphoric) and two organic acids (citric and malic) were tested at three concentration levels. At approximately equal levels of overall sensory impact, the inorganic acids were alike in astringency and sourness, receiving higher ratings for roughing and drying, and lower ratings for sourness than the organic acids. Interactions with concentration (differences in psychophysical functions) for the subquality of drying were noted, in addition to the differences in the astringent subqualities of roughing and drying seen across acids in both experiments. The higher level of astringency for inorganic acids suggests that the current model for tannin binding to salivary proteins as an explanation of astringency needs to be extended to include a direct pH-dependent effect.