Solutions properties and solute–solvent interactions in ternary sugar–salt–water solutions A.M. Seuvre a,b, * , M. Mathlouthi c a ENSBANA, Laboratoire EMMA (Eau – Molécules actives – Macromolécules – Activités), Université de Bourgogne, 1 Esplanade Erasme, 21000 Dijon, France b IUT Génie Biologique, Université de Bourgogne, Bd Docteur Petitjean, BP 17867, 21078 Dijon Cedex, France c Laboratoire de Chimie Physique Industrielle, UMR FARE 614, Université de Reims Champagne-Ardenne, BP1039, 51687 Reims Cedex, France article info Article history: Received 4 December 2008 Accepted 27 April 2009 Keywords: Viscosity Apparent molar volume Sugars Aqueous salt solutions Hydration Interaction abstract Viscometric constants were used to provide information on solute–solvent interactions in ternary water– sugar–salt solutions. Comparison was made between pure water and aqueous salt solution as solvents affecting the behaviour of small carbohydrates. The determination of intrinsic viscosity was made more accurate by applying triple extrapolation of the three equations (Huggins, Kramer and Meffroy-Biget). Results obtained with this triple extrapolation method were compared to that obtained with the Jones–Dole equation usually used. The B coefficient of the Jones–Dole equation was interpreted in terms of its components (B size ) and (B structure ), respectively assigned to the hydrodynamic volume and the con- tribution to solvent structural change. The determination of the apparent molar volumes in pure water enabled calculation of the hydration numbers. The determined apparent molar volumes of the studied sugars in aqueous salt solutions suggested a dehydration of the sugars explained by sugar–salt interac- tions. The most important perturbations observed in LiCl solutions compared to those in NaCl solutions were explained by LiCl being surrounded with more water molecules. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Small carbohydrates in aqueous solution are known to establish hydrogen bonds with water. The number and strength of these bonds depend on solute conformation (disposition of the hydroxyl groups in space), anomeric effect and on the proportion of ring iso- mers (pyranose or furanose) at equilibrium in solution. For exam- ple, D-glucose and D-galactose molecules in aqueous solution adopt the pyranose conformation while D-fructose presents an equilib- rium furanose ¡ pyranose (60% pyranose and 40% furanose) (Mathlouthi, 1980). Moreover, D-glucose and D-galactose have most of their hydroxyl groups in equatorial position (four and three, respectively). Equatorial OHs are more hydrated than are ax- ial ones because of a better fit with water structure. As a general rule, the solvent, because of its polarity, shows more or less affinity for solute, so that it controls its conformation and its solvation. In particular, sugar hydration is influenced by the stereochemistry of the solute and the molecular conformation (Franks, 1985). Different thermodynamic (Bonner & Cerutti, 1976; Dipaola & Belleau, 1977; Jasra & Ahluwalia, 1982) and spectroscopic studies showed that the hydration of a carbohydrate did not depend only on the number of OH groups and on the potential hydrogen bind- ing sites but also on their relative orientation. However, the con- clusions about their specific hydration are controversial (Harvey & Symons, 1978; Hoeiland & Holvik, 1978; Suggett & Clark, 1976). Furthermore, the water structure is influenced by other solutes, particularly by the ions arising from the dissolution of the electro- lytes. Na + and Li + are known to promote the structure of the water and the neighbouring water molecules are in a state more stable than in pure water (Moon & Jhon, 1986). While studies of carbohydrate–water and salt–water systems do not always lead to definitive conclusions, studies of solutions containing carbohydrate–salt–water systems are more complex and yet of a great interest since the interactions in aqueous solu- tions between carbohydrates and salts concern the biological area where there is coexistence between sugars and salt molecules. The intermolecular interactions of sugars in dilute aqueous solutions play an important role in governing the biological mechanisms of animal and plant life. The introduction of salts to the medium in- duces perturbations in the carbohydrate–water interactions. Vis- nhu and Misra (1977) observed an increase of the organisation of the water molecules with sodium salts in aqueous solutions of su- crose. Mohanty, Das, and Das (1981) have studied the KCl–water– sucrose system, using viscosity to show that KCl is able to break the structure of water, while Kaminsky (1957) suggested that breakdown of the structure of water can arise either from sucrose or from KCl. Banipal, Gautam, Dua, and Banipal (2006) studied the 0308-8146/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2009.04.101 * Corresponding author. Address: IUT Génie Biologique, Université de Bourgogne, Bd Docteur Petitjean, BP 17867, 21078 Dijon Cedex, France. Tel.: +33 3 8039 6843; fax: +33 3 8039 6611. E-mail address: amseuvre@u-bourgogne.fr (A.M. Seuvre). Food Chemistry 122 (2010) 455–461 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem