Poster and Slide Presentations Effects of alkaline pH on the apparent molar compressibilities of sweeteners

摘要

Magnesium hydroxide solution (saturated at 200C) was added to aqueous solutions of sucrose or sodium saccharin in order to measure solution parameters in relation to possible taste effects. Mannesium was chosen because it is known to be a net structure-maker and its double positive charge creates tenacious water-binding propensities and a corresponding negative contribution to apparent molar volume (—3 lcm3molT1). The use of magnesium hydroxide, rather than a magnesium salt at pH 7.0, avoids a concomitant positive contribution to partial molar volume from the anion. At pH 8.5 the magnesium concentration is <1.0% of the total concentration of sweetener (11.0—30.0% w/v) and thus contributes insignificantly to the measurable density. Hence, apparent specific volumes were unaltered by the presence of mag-nesium hydroxide. However, apparent molar isentropic compres-sibilities, measured by changes in ultrasound velocity showed sensitive differences in the presence of magnesium hydroxide. In all sweetener solutions, sucrose or sodium saccharin, the magnesium hydroxide elevates the apparent molar isentropic compressibility by up to 2.34 x 10A moP1bar1, which means that the compact-ness of the hydration layer around the solute is not as great in the presence of magnesium hydroxide. Although apparent specific volume is better established as an indicator of taste quality than is apparent specific isentropic compressibility, the former may be relatively insensitive in experimental conditions such as these. Both parameters show similar trends since both are related to water interactions and molecular packing characteristics. Elevation of apparent molar isentropic compressibility means that the solution approaches more closely to the open structure of pure water. The resulting water mobility advantage in the vicinity of ion-channels may thus explain the reports of certain cations as sweet taste enhancers.