Exopolysaccharide-milk protein interactions in a dairy model system simulating yoghurt conditions

Although exopolysaccharides (EPS) produced by lactic acid bacteria can be used to modulate the rheological and physical properties of fermented milk, the interactions between EPS and milk proteins in such complex system remain poorly understood. This work aimed to study the interaction between EPS with different structural characteristics and caseins in the absence or presence of whey proteins in a dairy model system simulating yoghurt conditions. The study was expected to highlight the contribution of whey proteins to the casein network and identify possible interactions of EPS with the casein network. Four starters were used: HC15/210R (control), HC15/291 (neutral, stiff, branched EPS), HC15/702074 (neutral, flexible, highly branched EPS), and 2104/210R (anionic, stiff, linear EPS). Fermentation was performed at 42 C until the pH reached 4.6. Microstructure and rheological and physical properties (syneresis, elastic modulus, and apparent viscosity) were measured. The diversity of EPS functionalities depended on the specific structures of the EPS: stronger gels were formed with the anionic EPS from strain 2104 probably because of electrostatic interactions, although limitation of syneresis was more influenced by the neutrality and stiffness of the EPS backbone of strain 291. The sequential addition of casein and whey proteins to the dairy model system revealed their individual contribution to the microstructure of the protein network. This study showed that the rheological and physical properties of fermented milk can be modulated by the casein and whey protein concentrations and the use of different EPS with specific structural characteristics.