An alternate mechanism for the astringent sensation of acids

Tannic acid was added to saliva, the pH was adjusted to 12 different levels in the range 2.5-7.2 and light scattering was observed. The maximum light scattering occurred at pH 4.4, with considerably less scattering at both higher and lower pH. Saliva Without added tannic acid had a light scattering maximum at the same pH. The total polyphenol (Folin-Ciocalteu) content of saliva was determined with results between 53 and 93 mg/l. It is proposed that at least part of the mechanism for the astringent sensation of acids in water is caused by an intensification of the interaction between salivary protein and salivary polyphenol. When acid is not present the interaction is less intense and the perception is weak or non-existent. The increased precipitation of salivary protein when acid is added to polyphenol also accounts for the observed increase in astringency. (C) 2003 Elsevier Ltd. All rights reserved.