Effects of lipids on the water sorption, glass transition and structural strength of carbohydrate-protein systems.

Encapsulant systems are gaining wide practical interest due to their functional and nutritional properties. This paper was focusing on understanding structural relaxations in that systems near glass transition temperature. Freeze-dried trehalose-whey protein isolate-sunflower oil systems with various ratios of the last were used as a carbohydrate-protein-lipid food model. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used as a tool to model water sorption isotherms. The glass transition temperature was obtained by differential scanning calorimetry (DSC). Structural α-relaxation temperatures were measured by dynamical mechanical analyses (DMA), dielectric analysis (DEA) and combined to cover a broad range for strength assessment. The microstructure was characterized by optical light microscopy, confocal laser scanning microscopy and scanning electron microscopy. The C1 and C2 constants for Williams-Landel-Ferry (WLF) equation and structural strength parameter were calculated for each system. The effect of sunflower oil and water contents on strength of carbohydrate-protein system was analyzed. Strength shows decreasing with increasing of lipid concentration in the mixtures and more complex dependence on the water content in a system.

Structural strength analysis of amorphous trehalose-maltodextrin systems.

Fundamental knowledge of physical state of materials gives practically important information for food, biological and pharmaceutical industry. Based on Williams-Landel-Ferry (WLF) equation, the strength concept was introduced. This concept provides a simple parameter, S, to express resistance of solids to flow above the glass transition temperature. To develop this approach, miscible trehalose-maltodextrin (0:100; 20:80; 40:60; 60:40; 80:20 and 100:0) systems with different ratios of components were used in the present study. Such systems represent various food products including infant formula and many nutritional formulations. Amorphous solids were prepared from 20% solids in water solutions by freeze-drying. Fractional water sorption analysis of trehalose-maltodextrin miscible systems allows control of water content at high water activities. Glass transition temperatures were measured by DSC. DMA and DEA in a multi-frequency mode allowed determination of corresponding α-relaxation temperatures at various structural relaxation times. Volume rheology gives structural relaxation time - temperature dependence for high water content systems. The strength showed linear dependence on maltodextrin concentration and its value decreased significantly with increasing water content in miscible systems.