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

Abstract

Understanding the behavior of casein micelles (CM) in concentrated regimes is critical for the design of dairy unit operations such as drying or evaporation but also it is still scarce. In this work, the effect of the decrease in pH and the addition of a calcium salt on concentrated skim milk dispersions was examined by rheometric measurements at 25°C. Control samples (S1), samples with a pH of 5.8 (S2), and samples with 0.04 M CaCl 2 addition (S3) at different concentrations (40, 45, 48, 50, and 52% w/w) were analyzed through flow curves and oscillatory dynamic data by frequency sweep tests. All samples showed a clear shear thinning non-Newtonian behavior and a large dependence on concentration, dispersions being more fluid for samples S2 and S3. A viscosity model for microgels was used to obtain parameters related to the characteristic structure of systems. It was demonstrated that CM had a similar structure for the different physicochemical systems studied and that the decrease of pH and the addition of salt reduced the dispersion stability due to electrostatic and steric potential energy is depleted. Dynamic data showed that dispersions at the highest concentration had dominant and similar elastic behavior and weak gel character. A transition regime from fluid to gel was observed in samples S2 at 45% w/w. No samples obeyed the Cox-Merz rule. This study allowed gaining more understanding related to the structure of CM systems studied.

Influence of protein standardisation media and heat treatment on viscosity and related physicochemical properties of skim milk concentrate

“…viscosity, especially in unstandardised skim milks. It is important to note that the TS content achieved after evaporation (i.e., 46% TS) in this study was chosen so as to avoid skim milk gelation which occurs rapidly above 50% TS (Olivares, Achkar, & Zorrilla, 2016). The viscosity and WPNI of skim milk was most significantly affected by protein concentration followed by heat treatment, and finally by the type and mode of addition of the standardisation media.…”

Dissociation and coagulation of caseins and whey proteins in concentrated skim milk heated by direct steam injection

“…Interestingly, the structure and integrity of casein micelles remain unaltered in concentrated milk systems and the effects on micelle hydration, charge, and colloidal calcium phosphate are reversible upon dilution depending on temperature and time of storage. Viscosity changes were attributed to an increase in the volume fraction of casein micelles which can be considered as highly hydrated spherical microgel particles (Olivares et al 2016). High heat treatment of highly concentrated milks is relatively unusual to date due to immediate spray drying for preservation, low heat stability, and high fouling potential.…”

The effect of heat treatment on physicochemical properties of skim milk concentrate and spray‐dried skim milk powder

“…At a higher TS content, casein micelles are densely packed and their movement is restricted, which also contributes to a high viscosity (Olivares et al . 2016). High SMC viscosity (>100 mPa.s) is associated with various undesirable processing issues, that is pump failure, bearding and blockages of nozzles and product rework (Westergaard 2004).…”

“…During evaporation, the viscosity of skim milk concentrate (SMC) increases due to an increase in TS content and a reduction in the distance between particles due to water removal (Bienvenue et al 2003). At a higher TS content, casein micelles are densely packed and their movement is restricted, which also contributes to a high viscosity (Olivares et al 2016). High SMC viscosity (>100 mPa.s) is associated with various undesirable processing issues, that is pump failure, bearding and blockages of nozzles and product rework (Westergaard 2004).…”