Viscosity, microstructure and phase behavior of aqueous mixtures of commercial milk protein products and xanthan gum

The behavior of commercial milk protein/xanthan mixtures was studied at neu tral pH. Four milk protein ingredients; skim milk powder, milk protein conc entrate, sodium caseinate and whey protein isolate were considered. For the xanthan concentrations used, up to 1wt%, the viscosity of the mixtures was dominated by the viscosity of xanthan. Mixtures of xanthan with skim milk powder or milk protein concentrate showed phase separation, as seen by conf ocal micrographs, and phase diagrams have been established for these two sy stems. No visible phase separation was observed in the case of mixtures of sodium caseinate or whey protein isolate systems. However, mixtures of sodi um caseinate and xanthan, under certain conditions, showed formation of 'th read-like' xanthan-rich regions by confocal microscopy. We believe that the phase separation occurring in milk protein concentrate/xanthan or skim mil k powder/xanthan mixtures was a result of depletion flocculation of casein micelles by the xanthan macromolecules, but thermodynamic incompatibility w as likely to occur in sodium caseinate/xanthan mixtures. (C) 2001 Elsevier Science Ltd. All rights reserved.