Rheology and phase behavior of dense casein micelle dispersions

Abstract

Casein micelle dispersions have been concentrated through osmotic stress and examined through rheological experiments. In conditions where the casein micelles are separated from each other, i.e., below random-close packing, the dispersions have exactly the flow and dynamic properties of the polydisperse hard-sphere fluid, demonstrating that the micelles interact only through excluded volume effects in this regime. These interactions cause the viscosity and the elastic modulus to increase by three orders of magnitude approaching the concentration of random-close packing estimated at C(max) approximately 178 g/l. Above C(max), the dispersions progressively turn into "gels" (i.e., soft solids) as C increases, with elastic moduli G(') that are nearly frequency independent. In this second regime, the micelles deform and/or deswell as C increases, and the resistance to deformation results from the formation of bonds between micelles combined with the intrinsic mechanical resistance of the micelles. The variation in G(') with C is then very similar to that observed with concentrated emulsions where the resistance to deformation originates from a set of membranes that separate the droplets. As in the case of emulsions, the G(') values at high frequency are also nearly identical to the osmotic pressures required to compress the casein dispersions. The rheology of sodium caseinate dispersions in which the caseins are not structured into micelles is also reported. Such dispersions have the behavior of associative polymer solutions at all the concentrations investigated, further confirming the importance of structure in determining the rheological properties of casein micelle systems.

Origin of suppressed demixing in casein/xanthan mixtures

“…The static and dynamic properties of casein dispersions are well described by concepts used for polydisperse hard sphere colloids up to high concentrations close to the glass transition. [24][25][26][27][28] Xanthan is a rather stiff polysaccharide that forms helices in aqueous salt solutions. For renatured xanthan, i.e.…”

Rheological behavior of concentrated skim milk dispersions as affected by physicochemical conditions: change in pH and CaCl2 addition

“…Moduli G′ and G″ of this dispersion did not scale as f 2 and f 1 , respectively, indicating that the dispersion does not behave as a classical viscoelastic fluid at low frequencies (Macosko 1994) but it is in a transition regime from liquid to gel (Bouchoux et al 2009). As pH decreases, colloidal calcium phosphate (CCP) is solubilized (Philippe et al 2003).…”

“…Bouchoux et al (2009) reported that CM are forced to deform and deswell at ϕ > 0.78. The authors stated that there are two possible sources of elastic resistance to deformation: the resistance to deformation of the CM themselves (due to the elasticity of their interfaces) and the resistance of nonpermanent bonds between CM.…”

“…where W (−) is the milk powder mass fraction, ρ (g.mL −1 ) is the dispersion density at a defined temperature that was calculated as suggested by Choi and Okos (1986) taking into account the composition of the skim milk powder used (35% w/w protein, 50% w/ w carbohydrate, 1.5% w/w fat, 8.5% w/w ash, and 4% w/w moisture), and υ is the CM voluminosity (υ = 4.4 mL.g −1 ; Bouchoux et al 2009;Dahbi et al 2010;de Kruif 1998). The percentage of caseins in the total protein content of milk of 78.3% was used as suggested by Walstra et al (2006).…”

“…Indeed, CM are the main contributors to the skim milk rheology (Bienvenue et al 2003;Karlsson et al 2005;Liu et al 2012). However, information about how the CM behave and interact in such concentrated regimes is still scarce (Bouchoux et al 2009;Dahbi et al 2010;Dalgleish and Corredig 2012;Qu et al 2015). Concentration of skimmed milk is an important unit operation in a number of dairy processes.…”