CALORIMETRIC STUDY OF THE GLASS-TRANSITION OCCURRING IN AQUEOUS GLUCOSE - FRUCTOSE SOLUTIONS

Glass transition temperatures (T(g)) for dilute and concentrated gluco se:fructose:water solutions have been determined by differential scann ing calorimetry. The supplemented phase diagrams (glucose: fructose 1: 4, 1:2, 1:1. 2:1, 4:1 (w/w)) are presented and from these the temperat ure (T(g)') and concentration (C(g)') of the maximally freeze-concentr ated glass have been determined. Theoretical predictions of T(g) for b inary (glucose:fructose) and tertiary (glucose:fructose:water) systems according to the Couchman-Karasz and Gordon-Taylor equations are give n and discussed. Annealing vitrified glucose: fructose glasses above t heir T(g) allows the glass concentration to approach C(g)' as a result of ice formation. Viscosity measurements of fructose and fructose:glu cose mixtures allow for a calculation of T(g) of the non-aqueous solut ions.