Physicochemical properties and vibrational spectra of small carbohydrates in aqueous solution and the role of water in their sweet taste

Solution properties (intrinsic viscosity, apparent specific volume, hydration number and surface tension) were determined for three nutritive sugars (d-glucose, d-fructose and sucrose) and three polyols (xylitol, sorbitol and lactitol) in water and in 1% (ww) aqueous salt (NaCl, KCl or MgCl2) solution. Likewise, the laser-Raman spectra of these carbohydrates in water (10% ww) or in salt solutions were recorded in the OH stretching region (3800−2800 cm−1) and analysed by comparison to the Raman band of water fitted to 4 Gaussian components. Microwave spectra of saturated sugar solutions were also obtained and interpreted in terms of polarity of the sugars. Comparison of the physicochemical results and Raman data in water, on the one hand, and in salt solution on the other, permitted determination of the influence of the biologically important cations (Na+, K+ and Mg2+) on the effect of sugars and polyols on water structure. This is also useful to support our three-step model of sweet taste chemoreception which relies on the fact that water mobility and the polarity of stimulant are the clue to the elucidation of the sweetness mechanism.