Modification of the WLF model for characterization of the relaxation time-temperature relationship in trehalose-whey protein isolate systems

•Tg and Tα are strongly dependent on water content and less dependent on protein content in a carbohydrate-protein system.•New “strength” parameter combines the material state of the system and a practically important time factor.•New “strength” parameter is increasing upon addition of protein to the system.

Understanding structural relaxations is an important task for materials engineering in biological, food, polymer and pharmaceutical areas. By now a number of theoretical models for describing structural relaxation were developed. Nevertheless, the complicity of real systems requires more detailed investigation and development of appropriate mathematical models. In the present study trehalose-WPI system was used as a carbohydrate-protein model. The ratio of components was varied over the range 0–100% with 20% intervals. The experimental part consisted of tree main sections: (1) sample preparation and preliminary analysis (water content, water sorption, freeze drying), (2) thermal (DSC) and mechanical (DMA) analyses, (3) rheology of high water content systems. Water sorption isotherms were plotted, glass transition and α-relaxation temperature were obtained for each system. Based on the WLF relationship, the “strength” parameter: S=dC2C1−d was defined, where d is the critical decrease of τ (from 100 to 0.01 s) on the logarithmic scale, C1 and C2 – the “non-universal” constants in WLF equation. For all systems dependence of the “strength” parameter on the composition and water content was established.