Thermophysical properties of amorphous dehydrated and frozen systems, as affected by salts

MAZZOBRE, MARÍA FLORENCIA; LONGINOTTI, M. PAULA; CORTI, HORACIO ROBERTO; BUERA, MARÍA DEL PILAR

Amorphous Food and Pharmaceutical Systems

RSC Publishing

Lugar: Cambridge; Año: 2002; p. 231 - 243

Upon the change from an amorphous to a crystalline structure, deteriorative reactions may be accelerated in dehydrated or frozen systems. Although electrolytes have a universal presence in biological systems and pharmaceutical formulations, their effect on the thermophysical properties of sugar systems has not been fully investigated. The objective of the present work was to explore the effects of salts on water sorption, sugar and ice crystallization characteristics, and transport behaviour in trehalose and sucrose systems in supercooled or freeze-dried glassy systems. The water sorption properties, ice crystallization, and ice melting characteristics of sugar-water systems were modified by the presence of salts, at levels of mass fraction of water (w) £ 0.4, without affecting the glass transition temperature (Tg) values of the systems. The presence of salts seemed to constrain the dimensionality of sugar crystal growth, probably due to changes in nucleation mechanism. Results from electrical conductivity measurements showed that large positive deviations from the Walden rule occur in sugar-salt systems. The observed changes in the properties of salt-containing systems could be attributed to local heterogeneities, induced by ionic species, in supercooled solutions.