Composition, thermal and rheological behaviour of selected Greek honeys

Several chemical and physicochemical properties (sugar composition, water content, water activity, colour, viscosity, thermal properties) were determined for 33 Greek honeys from different botanical and geographical origin. The water content and water activity values varied within 13.0-18.9 g/100 g and 0.528-0.663, respectively. Steady shear and dynamic rheological tests revealed Newtonian behaviour for all samples examined over the temperature range of 20-60 degreesC. The steady shear viscosity (eta) and loss modulus (G(n)) were inversely related to the water content of honey. The temperature dependence of viscosity followed both the Arrhenius and the Williams Landel-Ferry models; for the latter model the viscosity data of different samples fitted very well into a common master curve. The glass transition temperature (T-g) of honeys, as determined by differential scanning calorimetry, varied between -34 and -47 degreesC depending on their composition. The plasticizing action of water on honey solids was evident for native samples as well as among diluted and concentrated honeys; T-g decreased with increasing water content. Despite a broad variation in sugar composition among the samples, the T-g values vs. water content fitted reasonably well to the Gordon-Taylor empirical equation. (C) 2003 Elsevier Ltd. All rights reserved.