Electrical responses of a water/octanol/water liquid membrane to taste substances

Examination was made of electrical potential oscillation across the liquid membrane of a water/octanol/water system in the presence of five types of primary taste substances, imparting bitterness (quinine hydrochloride and berberine hydrochloride), sweetness (sucrose and glucose), sourness (hydrochloric acid and citric acid), saltiness (sodium chloride and potassium chloride) and umami (sodium glutamate and sodium inosinate) at concentrations from 0.01 mM to 1 M. Each exerted effect on the mode of oscillation, particular so on the potential of the liquid membrane immediately following contact of the octanol solution with the aqueous solutions, potential just before oscillation and low potential of the first oscillation. The effects of substances in the same taste category on oscillation were essentially the same. Effect intensity showed the following order: bitter approximate to sour < salty approximate to umami < sweet substances. The oscillation mode for drugs (dextromethorphan hydrobromide and doxycycline hydrochloride) corresponded to that due to bitter substances, and the drugs and 10% simple syrup (a flavoring agent prescribed by the Japanese Pharmacopoeia), sweet substances. It thus follows that the degree of modification of drug bitterness by simple syrup may be evaluated by the octanol membrane.