Structural heterogeneity and its effect on the glass transition in sucrose solutions containing protein and polysaccharide

Foods systems containing polysaccharides and proteins tend to be structurally heterogeneous due to polymer incompatibility and phase separation, at least on a microscopic scale. This study was designed to determine the effect of such phase separation on the bulk glass transition temperature of frozen solutions containing sucrose, lactose, milk salts, protein from skim milk powder and guar or locust bean gum. The glass transition temperature of sugar-containing solutions was increased by the presence of polymer (protein or polysaccharide). However, the bulk glass transition temperature of microscopically phase-separated systems was dominated by the protein phase, suggesting that theoretical determinations of complex systems based solely on composition may fail to accurately predict glass transition temperatures, due to component structural heterogeneity. It was also shown that there was a difference in the amount of glass that formed within each domain, due to differential concentrations of the phase-separated polymer and its effect on dilution of the sugars in true solution. This may also affect predicted glass transition temperatures. (c) 2005 Elsevier Ltd. All rights reserved.