In situ exopolysaccharides from Lactobacillus helveticus MB2-1 in Sayram ketteki yoghurt: Set yoghurts properties and interactions with sodium caseinate

The effects of high exopolysaccharides (EPS) - producing Lactobacillus helveticus MB2-1 on the structure and storage stability of set yoghurts, and the interactions between its EPS (molecular weight 9.34 × 104 Da) from Sayram ketteki yoghurt (SKY) and sodium caseinate (CAS) were studied. The rheology, microstructure, texture and storage stability of the three set yoghurts including control yoghurt (Control), adding-probiotic yoghurt (APY) and SKY were investigated, which showed that the SKY exhibited less shear thinning than the Control and APY, and the textural indexes and storage stability of the SKY were significantly better than that of other two yoghurts (p < 0.05). Moreover, the increased turbidity, decreased ζ potential and surface hydrophobicity of EPS/CAS complex coacervation were determined at EPS/CAS mass ratio of 3 (corresponding to 0.33 g/L of CAS and 1 g/L of EPS), mainly owing to the electrostatic attraction of the two biopolymers to form aggregates. Besides, the higher sizes and more aggregation of EPS/CAS complexes were formed at pH 3.5. Taken together, the results indicated that the high EPS-producing characteristic of L. helveticus MB2-1 could positively influence the qualities of set yoghurts, and the EPS/CAS complex coacervation in dairy products was closely related to the EPS/CAS mass ratio and pH condition.