Bitter taste mechanism

Noble, A.C., Astringency and bitterness of flavonoid phenols. In Chemistry of Taste Mechanisms, Behaviors, and Mimics (eds P. Given and D. Paredes), American Chemical Society, Washington, DC, 2002, p. 192. 

Many bixxer compounds contain both hydrophobic and hydrophilic sites which can alter cell membranes through penetration. There is a correlation between bitter intensity and hydrophobicity-solubility indexes such as fee octanol/water partition coefficient, lo (7). Penetration may directly affect cAMP phosphodiesterase as part of fee transduction process (see below). A bitter receptor protein may be involved wife certain bitters, such as specific structural requirements wife fee bitter tasting dipeptides and denatonium salts (27). The latter is used in some consumer products to avoid accidental ingestion. A receptor mechanism is also supported by fee existence of a genetic "taste blindness" for some bitter materials (see below). 

Tablets are often coated to protect the drug from the external environment, to mask bitter tastes, add mechanical strength, or to enhance ease of swallowing. A coating can also be used for aesthetic or commercial purposes, improving product appearance and identity.

Bitter taste is elicited by structurally diverse compounds, including phenols, ions, amino acids and peptides, alkaloids, acylated sugars, glycosides, nitrogenous compounds, and thiocarbamates. Taste receptor cells are primarily associated with papillae on the tongue. The signal transduction mechanisms by which taste perception occurs are well not understood, but are the focus of intensive research as reviewed recently (6). 

The only product in this category that has been adequately studied is Listerine. Listerine is a mixture of essential oils—thymol, menthol, a eucalyptol, and methylsalicylate. The mechanism of action appears to be related to alteration of the bacterial cell wall. This product is uncharged and has a low substantivity. Adverse effects reported have been a burning sensation and bitter taste. It is available in a 21.6-26.9% alcohol vehicle with a pH of 4.2. Recommended usage is twice daily, and the ADA accepts the product and some of its generic copies for the control of plaque and gingivitis. 

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