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Received December 26, 2001; accepted March 19, 2002
Purpose. NaCl has proven to be an effective bitterness inhibitor, but the reason remains unclear. The purpose of this study was to examine the influence of a variety of cations and anions on the bitterness of selected oral pharmaceuticals and bitter taste stimuli: pseudoephedrine, ranitidine, acetaminophen, quinine, and urea.
Method. Human psychophysical taste evaluation using a whole mouth exposure procedure was used.
Results. The cations (all associated with the acetate anion) inhibited bitterness when mixed with pharmaceutical solutions to varying degrees. The sodium cation significantly (P < 0.003) inhibited bitterness of the pharmaceuticals more than the other cations. The anions (all associated with the sodium cation) also inhibited bitterness to varying degrees. With the exception of salicylate, the glutamate and adenosine monophosphate anions significantly (P < 0.001) inhibited bitterness of the pharmaceuticals more than the other anions. Also, there were several specific inhibitory interactions between ammonium, sodium and salicylate and certain pharmaceuticals.
Conclusions We conclude that sodium was the most successful cation and glutamate and AMP were the most successful anions at inhibiting bitterness. Structure forming and breaking properties of ions, as predicted by the Hofmeister series, and other physical-chemical ion properties failed to significantly predict bitterness inhibition.
KEY WORDS: bitter taste; bitterness blocking; salts; taste psychophysics; pseudoephedrine; ranitidine; acetaminophen.
ABBREVIATIONS: NaAc, sodium acetate ; COMAc, combined cations; (NaAc, NH4Ac, MgAc, KAc, CaAc) NH4Ac , ammonium acetate; MgAc, magnesium acetate; Kac, potassium acetate; CaAc, calcium acetate; MSG, monosodium glutamate; NaAMP, adenosine monophosphate; NaCl, sodium chloride; NaSal, sodium salyiclate; NaGlc, sodium gluconate; Na2GP, di-sodium glycerophosphate; Na2Phos, di-sodium phosphate; NaProp, sodium propionate; COM, combined anions; (MSG, Cl, Glc, Sal, I) Na2SO4, di-sodium sulfate; NaI, sodium iodide; KI, potassium iodide; PHCL, pharmaceutical.
INTRODUCTION
Excessive bitterness of the active compounds in oral liquid formulations is a major taste problem facing the pharmaceutical industry. Bitterness of formulations can influence pharmaceutical selection by physicians and patients and affect compliance with prescribed regimens (1,2). Consequently, many methods to inhibit or block bitterness, both chemical and physical, have been employed. A few examples are: the addition of sweeteners, lipids and emulsifiers, carbohydrates, proteins and flavors, and the encapsulation of the active compound (3); none of these methods is fully successful. Moreover, the problem...