Rheological evaluation of gelatin-xanthan gum system with high levels of co-solutes in the rubber-to-glass transition region

Effects of moisture content, xanthan gum (XG) addition, and glucose syrup (GS):sucrose ratio on the gelation of gelatin-XG systems with high levels of co-solutes were investigated in the rubbery and the glass transition regions. Frequency sweep tests were performed between 0.1 and 100rad and the storage (G') and loss (G') moduli of the system were measured in the temperature range of 60 to -15°C. The onset of glass transition region increased with decreasing moisture content. The time-temperature superposition yielded master curves of G' and G' as a function of timescale of measurement. G' and G' were superimposed with the horizontal shift factor a_T, which was temperature dependent according to the Williams-Landel-Ferry (WLF) equation. Glass transition temperature (T_g) of the samples were determined by dynamic mechanical analysis (DMA) from the peak of tan. δT_g decreased with XG addition. The energy of vitrification of samples with XG increased compared to samples containing only gelatin. Relaxation spectra of the samples were calculated from rheological measurements using the first and second approximations. The Rouse theory was more closely followed with the second approximation.