title: Effect of molecular structure and water content on the dielectric relaxation behaviour of amorphous low molecular weight carbohydrates above and below their glass transition.
abstract: The dielectric relaxation behaviour of several amorphous low molecular weight carbohydrates and their 10% w/w water mixtures has been studied in the supercooled liquid and glassy regions in the frequency range 100 Hz to 100 kHz. The dry carbohydrates show a primary alpha-relaxation (activation energy 250-405 kJ mol(-1)) at temperatures above the calorimetric glass transition temperature, Tg, and, in most cases, a secondary beta-relaxation (activation energy 42-55 kJ mol(-1)) at sub-Tg temperatures. Whilst D-mannose showed a beta-relaxation similar in strength to D-glucose, its deoxy sugar, L-rhamnose showed a relatively weak beta-relaxation. This indicates that the hydroxymethyl group influences relaxation in carbohydrate glasses. Addition of water shifted the alpha-relaxations to lower temperatures and increased the strength of the beta-relaxations. In glucitol this resulted in a merging of the alpha- and beta-relaxations. The beta-relaxation increased in strength and decreased in temperature for the series of water mixtures: D-glucose, maltose, and maltotriose.
authors: Institute of Food Research, Food Materials Science Division, Colney, Norwich, UK.
authors: T R
authors: TR
authors: Noel
authors: R
authors: R
authors: Parker
authors: S G
authors: SG
authors: Ring
mesh_terms: D002152:Calorimetry, Differential Scanning; D002241:Carbohydrates / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D014867:Water