Origin of suppressed demixing in casein/xanthan mixtures

Abstract

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* ¼ 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.

Introducing Diffusing Wave Spectroscopy as a Process Analytical Tool for Pharmaceutical Emulsion Manufacturing

“…Therefore, the use of DWS allowed to identify a second crossover at high frequencies for all emulsions, where G′′ prevailed over G′ . This second crossover has been previously observed and it reflects the short‐time relaxation and dissipation mechanisms in the system …”

“…Therefore, the use of DWS allowed to identify a second crossover at high frequencies for all emulsions, where G prevailed over G . This second crossover has been previously observed 42,50 and it reflects the short-time relaxation and dissipation mechanisms in the system. 51 The results indicate that the xanthan-containing emulsions were viscoelastic, with a liquid-like behavior at very low frequencies, a gel-like structure at higher frequencies, and again a dissipation dominated behavior at very high frequencies.…”

“…The mesh size of highly entangled solutions of semiflexible polymers has been described by Hinsch et al:where ξ is the mesh size and υ corresponds to the polymer density, that is, the number of polymers with contour length L c per unit volume. The typical contour length of xanthan is approximately 2 μm, and the molecular weight of this grade of xanthan has been reported to be approximately 2 × 10 6 Da . Taking these values into account, the mesh size for the continuous phase networks containing different concentrations of xanthan can be determined.…”

Intermittent dynamics and logarithmic domain growth during the spinodal decomposition of a glass-forming liquid

“…40 Moreover, bicontinuous disordered structures reminiscent of the ones obtained in spinodal decompositions may also be found in colorful bird feathers, and were recently interpreted as incompletely phase separated polymeric glasses, 41,42 thus demonstrating the broad relevance of the problem of the glass-gas phase separation. Finally, even more complex mixtures that are relevant to food processing 43 or solar cell technology [44][45][46] also exhibit kinetically arrested spinodal decompositions, that might result from the fact that one component becomes mechanically rigid.…”

Unexpected Decoupling of Stretching and Bending Modes in Protein Gels

“…Because of this difference the gels exhibit features of porous media, the elasticity increasing exponentially with φ instead of the typical power law increases observed in classical colloidal gels. Indeed, for colloidal systems, where spinodal decomposition is for instance induced by depletion [4,5,9,10,12,18,20], the arrest of the phase separation process generally leads to gels where the ratio between particle and strand size barely exceeds one order of magnitude. Both, bending and stretching modes should here still contribute to the elasticity of the system; however, it is unlikely that both modes will be as clearly separated in time, as this is the case in the lysozyme gels.…”