Carbohydrates glass transition temperature

Levi, G. and Karel, M. 1995. Volumetric shrinkage in freeze-dried carbohydrates above their glass transition temperature. Food Res. Int. 28, 145-151. 

Torreggiani, D., Fomi, E., Guercilena, I., Maestrelli, A., Bertolo, G., Archer, G.P., Kennedy, C.J., Bone, S., Blond, G., Contreras-Lopez, E., and Champion, D. 1999a. Modification of glass transition temperature through carbohydrates additions Effect upon colour and anthocyanin pigment stability in frozen strawberry juices. Food Res. Int. 32, 441 146. 

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). 

Control of moisture is one area of great value to food systems. Low molecular weight carbohydrate materials interact with water in ways that can be measured physically and used to predict physical properties. For example, the influence of molecular weights of saccharides on glass transition temperature has been studied [77] to understand their impact on food system proper-... 

Thus it is clearly visible that they are about 40-50 K higher than the value of Tg evaluated on the basis of dielectric measurements for acetyl derivative of lactose. It is surely related to the fact that molecules of the reduced disaccharide form strong hydrogen bonds and mainly these interactions are responsible for so significant difference in the glass transition temperatures of the both investigated herein carbohydrates. Influence of hydrogen bonds on structural... 

Torreggiani, D., Fomi, E., Guercilena, I. et al. 1999. Modification of glass transition temperature through carbohydrates additions Effect upon color and anthocyanin pigment stability in frozen strawberry juices. Food Research International 32 441-446. 

Fig. 6.4-6 Effect of water on the glass-transition temperature of several carbohydrates, calculated with the Gordon-Taylor equation [B.108]...

Because water plasticizes hydrophilic food components, their glass transition is strongly dependent on water content. The effect of water on the glass-transition temperature of several amorphous carbohydrates, calculated with the Gordon Taylor equation [B.79], is depicted in Fig. 6.4-6. Within the range of the materials shown, Tg decreases with lower average molecular weight and/or increased concentration of plasticizer (water). 

Regarding the thermal properties of lignosulphonates, when examined by differential scanning calorimetry (DSC), they do not exhibit a glass transition temperature. In high temperature DSC decomposition runs they show two peaks, one at about 320°C and the other at about 450°C. The first peak is associated with the degradation of carbohydrates and the second with lignin itself [26]. 

Industrial kraft lignin exhibits a glass transition temperature at around 140°C. In high tenperature decomposition runs, it exhibits a multiplet peaking at 452°C with two shoulders at 432°C and 482°C. This is in contrast to ligno-sulphonates, which display no glass transition temperature and have a low temperature degradation peak because of their carbohydrate content [26]. 

According to the glass transition theory, lipids are dispersed in the free volume of the food matrix composed of carbohydrates and protein polymers. In the rubbery state, the lipids react readily with oxygen and become oxidized. In the glassy state, however, the lipids are stable to oxidation because they are encapsulated and there is no free volume. The glass transition temperature, which determines when the food matrix changes from one state to the other, increases with a decrease in moisture and water activity. In many foods the... 

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