pH-Dependent interaction between sodium caseinate and xanthan gum

Xanthan gum and sodium caseinate are used to improve stability and texture of food. To investigate interactions between them, the effects of pH on structure of sodium caseinate–xanthan gum complex were analyzed. HCl titration showed that the absorbance of the mixture was different from that of sodium caseinate alone throughout the acidification, and that syneresis in the mixture was delayed in acidic pH. Rennet digestion clarified that xanthan gum retarded degradation of κ-casein at pH 2.7. Atomic force microscopy revealed that xanthan gum interaction with sodium caseinate was pH-dependent. Sodium caseinate particles were individually bound with xanthan gum at pH 6.6, and a side-by-side aggregation of sodium caseinate along xanthan gum was observed at pH 4.2. The mixture formed a network composed of rod-like fibers at pH 2.7. These results indicate that hydrophobic and electrostatic interactions play a role in the complex formation at neutral and acidic pH, respectively.