Mahtab Hassandokht Firouz - Department of Food Science and Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences and Health Services, Tehran, Iran
Mohammad Amin Mohammadifar - Department of Food Science and Technology, Faculty of Nutrition Sciences and Food Technology/National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences and Health Services, Tehran, Iran
Ghasem Fadavi - Department of Food Science and Technology, Faculty of Food Industry and Agriculture, Standard Research Center, Karaj, Iran

The knowledge of non-covalent interactions between proteins and polysaccharides is of the utmost importance in the development of engineered food materials, as the structure, function and stability of these composite food systems are primarily determined by macromolecular interactions. In the present study, electrostatic interactions and the subsequent associative phase separation of total gum tragacanth (TGT) and its soluble fraction, tragacanthin (T), with β-lactoglobulin (BLG) were investigated in aqueous medium as a function of pH (2.00–6.00) using spectrophotometry, light scattering and, in situ and continuous viscosity measurements. The results obtained by these complementary methods, allowed the associative phase separation process to be characterised in terms of five pH-delimited zones at which critical transitions took place. Both mixtures followed a similar trend, suggesting the occurrence of similar mechanism of complexation/ phase separation under our experimental conditions. Some small differences were however noticed. Indeed, the characteristic pH values associated with structural transitions in BLG+TGT mixtures were slightly higher and the kinetic of phase separation was faster. It was found that the assembled structures experience a progressive contraction process upon complexation. Interestingly, complexation of BLG and T at pH 4.30 led to the formation of nano-particles (d <60 nm).

Gum Tragacanth, β-lactoglobulin, Associative Phase Separation, Complexation