Relationship Between Physical Properties of Casein Micelles and Rheology of Skim Milk Concentrate

Abstract

The properties of casein micelles in milk concentrates are of interest for the use of ultrafiltered (UF) skim milk concentrates in dairy products, and for the general understanding of colloidal stability and behavior of the casein micelle. The rheological behavior of UF skim milk concentrate with a casein concentration of 19.5% (wt/wt) was investigated at different pH and NaCl concentrations by analyzing flow viscometry and small amplitude oscillatory shear measurements. Viscometric flow curves were fitted to the Carreau-Yasuda model with the aim of determining values for the viscosity at infinite high shear rates and thereby estimate the voluminosity of the casein micelles (nu(casein)) in the UF concentrate. The voluminosity of the casein micelles increased with addition of NaCl and decreased when pH was decreased from 6.5 to 5.5. At pH 5.2, nu(casein) increased because of acid-induced aggregation of the casein micelles. The changes in nu(casein) could be interpreted from transmission electron microscopy of freeze-fractured samples of the UF concentrate and partly from dynamic light scattering measurements. Altered interactions between casein micelles due to different pH and NaCl concentrations are proposed to occur due to collapse of the kappa-casein layer, changed ionic strength, and altered distance between casein micelles.

Does ultrafiltration have a lasting effect on the physico-chemical properties of the casein micelles?

“…This change in pH is in agreement with previous reports (Karlsson et al 2005), and was accompanied by a change in the cation profile of the milk. Table 2 (Holt 1997).…”

“…The extent of the changes on colloidal calcium phosphate during UF depends mainly on processing conditions (such as temperature and pH of filtration), and micellar dissociation has been reported to occur during UF (Singh 2007). Changes in the chemical and physical properties of skim milk during membrane filtration have been extensively investigated (JimenezLopez et al 2008;Karlsson et al 2005); the casein micelles are recognized as key factors in the processing performance during filtration (David et al 2008;Piry et al 2008;Rabiller-Baudry et al 2005). However, the effects of UF on the structure function of the casein micelles have received very little attention.…”

Low shear rheological behaviour of two-phase mesophase pitch

“…It has been proposed that represents the viscous relaxation time, which is the time over which the viscosity changes from Newtonian to shearthinning, and is commonly referred to as the "Yasuda" constant which describes this transition; it is inversely related to the width of the transition zone [20]. The lines in Figures 3 to 7 are the fits based on this equation.…”

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

“…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).…”