Sucrose glass transition

The glass transition of solutes that remain amorphous during and after the freezing process can often be seen in the DSC thermogram as a shift in the baseline toward higher heat capacity. This is illustrated in the DSC thermogram of sucrose solution in Fig. 6, in which the glass transition is observed at — 34°C. 

To illustrate this more quantitatively, consider the hypothetical sucrose example discussed by Ahlneck and Zografi [80]. Assuming that all the sorbed water is taken up by the amorphous portion of material, 0.1% total moisture would correspond to approximately 20%, 10%, 4%, and 2% moisture content in the amorphous material, respectively, for 0.5%, 1%, 2.5%, and 5% of amorphous solid. The glass transition temperatures for the amorphous portions... 

Chen, Y.H., Aull, J.L., and Bell, L.N. 1999. Invertase storage stability and sucrose hydrolysis in solids as affected by water activity and glass transition. J. Agric. Food Chem. 47, 504-509. 

A simple relationship was not found between shrinkage and glass - rubber transitions of both peach and apricot tissue (Campolongo, 2002 Riva et al., 2001, 2002). Even when sorbitol use increased AT (= T — 7g ) values, both the color and the structure showed the highest stability. The fact that sorbitol performed better than sucrose indicates that the chemical nature of the infused solute is more important than its glass transition temperature in preventing structural collapse, in accordance with the results reported by del Valle et al. (1998). 

Glass Transition Temperature (Tg) of Amorphous Sucrose versus Water Content... 

Table 1.6.1 Glass transition temperature Tg and crystallization temperature Tc for amorphous sucrose, trehalose, lactose, raffinose and amorphous sucrose in the presence of absorbed water...

Fig. 1.27.1. DTA measurement of a 24% sucrose-6% NaCI solution during slow rewarming after quick (200 °C/min) freezing. 1, Glass transition at = 78 °C 2, growth of crystals (exothermic) at =52 °C 3, increase of c water is formed between the crystals 4, ice melts at = 7 °C (Figure 1 from [1.25])...

Fig. 1.29. Behavior of a su-crose-NaCI solution at different sucrose—NaCI concentrations and temperatures after quick freezing (200°C/min) during slow rewarming (Figure 8 from [1.25]). 1, Eutectic melting temperature of NaCI 2, crystallization temperature of NaCI 3, temperature at which the glass phase starts to soften 4, glass transition temperature...

Zeng, X.M., Martin, G.P., Marriott, C. Effects of molecular weight of polyvinylpyrrolidone on the glass transition and crystallization of co-lyophilized sucrose. Int. J. Pharm. 218, 63-73, 2001... 

Kouassi, K., Roos, Y.H. Glass transition and water effects on sucrose version in non-crystalline carbohydrate food systems. Food Res. Int. 34, 895-901, 2001... 

Both lactose and sucrose have been shown to crystallize in an amorphous form at moisture contents close to the glass transition temperature (Roos and Karel 1991a,b Roos and Karel 1992). When amorphous lactose is held at constant water content, crystallization releases water to the remaining amorphous material, which depresses the glass transition temperature and accelerates crystallization. These authors have done extensive studies on the glass transition of amorphous carbohydrate solutions (Roos 1993 Roos and Karel 1991d). 

Maltodextrins of varying molecular weights are plasticized by water and decrease the glass transition temperature. Maltodextrins retard the crystallization of amorphous sucrose and at high concentrations totally inhibit sucrose crystallization (Roos and Karel 1991c). 

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