Many food colloids contain polysaccharides as well as
proteins, and the presence of protein–polysaccharide
complexes can have a profound influence on structure,
stability and rheology. Furthermore, the phenomenon of
complex coacervation involving hydrocolloids like gelatin
and gum arabic has long had important practical
applications in the area of microencapsulation. Recent
advances in understanding this behaviour are reviewed by
de Kruif et al. (pp. 340–349). The authors demonstrate
the analogy between protein–polysaccharide complex
coacervation and colloidal gas–liquid phase separation,
insofar as the phase transition is mainly entropically
driven, and it disappears at high ionic strength. The
stoichiometry of the weakly charged protein–polysaccharide complex is considered to be mainly determined by the
polyion charge density, and the structure is considered to
be dynamic, with timescales varying from milliseconds to
days depending on the interaction strength. The coacervate phase is typically more viscous than elastic: it
resembles more the rheological behaviour of a concentrated particle dispersion than a viscoelastic polymer
solution. Unfortunately, these concentrated mixed polyelectrolyte systems are rather complicated to describe
theoretically due to the difficulty in properly representing
the correlated local charge distributions.
Many food colloids contain polysaccharides as well asproteins, and the presence of protein–polysaccharidecomplexes can have a profound influence on structure,stability and rheology. Furthermore, the phenomenon ofcomplex coacervation involving hydrocolloids like gelatinand gum arabic has long had important practicalapplications in the area of microencapsulation. Recentadvances in understanding this behaviour are reviewed byde Kruif et al. (pp. 340–349). The authors demonstratethe analogy between protein–polysaccharide complexcoacervation and colloidal gas–liquid phase separation,insofar as the phase transition is mainly entropicallydriven, and it disappears at high ionic strength. Thestoichiometry of the weakly charged protein–polysaccharide complex is considered to be mainly determined by thepolyion charge density, and the structure is considered tobe dynamic, with timescales varying from milliseconds todays depending on the interaction strength. The coacervate phase is typically more viscous than elastic: itresembles more the rheological behaviour of a concentrated particle dispersion than a viscoelastic polymersolution. Unfortunately, these concentrated mixed polyelectrolyte systems are rather complicated to describetheoretically due to the difficulty in properly representingthe correlated local charge distributions.
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