Faculté des sciences

Origin of suppressed demixing in casein/xanthan mixtures

Gruijthuijsen, Kitty van ; Herle, Vishweshwara ; Tuinier, Remco ; Schurtenberger, Peter ; Stradner, Anna

In: Soft Matter, 2012, vol. 8, no. 5, p. 1547-1555

We explore the properties of casein/xanthan mixtures for xanthan concentrations beyond those inducing phase separation. Previous work has successfully described the onset of demixing by depletion theory in the protein limit, where the xanthan polysaccharides , the polymers , are larger than the caseins from skim milk powder, the colloids (S. Bhat et al., J. Phys.: Condens. Matter, 2006, L339). We... Plus

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    Summary
    We explore the properties of casein/xanthan mixtures for xanthan concentrations beyond those inducing phase separation. Previous work has successfully described the onset of demixing by depletion theory in the protein limit, where the xanthan polysaccharides , the polymers , are larger than the caseins from skim milk powder, the colloids (S. Bhat et al., J. Phys.: Condens. Matter, 2006, L339). We now extend these studies to xanthan concentrations in a range of c/c* = 13–88, aiming to arrest the phase separation via a (transiently) arrested casein-rich phase. Surprisingly, we find that the casein-rich phase remains fluidic deep into the two-phase region, with an equilibrium composition that significantly differs from predictions for mixtures of hard spheres plus flexible polymer chains in a good solvent . Furthermore, we show that macroscopic phase separation is arrested for c/c* > 60. Our investigations reveal that the rheological properties of the mixtures are fully determined by the xanthan-rich phase with characteristic long relaxation times that depend remarkably strongly on the xanthan concentration.