Impact of shear and pH on properties of casein micelles in milk protein concentrate

Properties of casein micelles can be manipulated by changing environmental conditions, which leads to formation of particles of varying sizes with different physical properties. This study evaluated the impact of shear (100 and 1000 s⁻¹) on the properties of casein micelles in milk protein concentrate in the pH range 2.0–7.5. Casein micelle size was not affected by shear at pH 6.7 or 7.5, whereas casein aggregates, which were formed at pH 4.6 and 2.0, had their size considerably reduced upon high shearing. The composition of the soluble phase was dependent on pH as increased concentrations of β-casein and α_s-caseins were found at pH 4.6 and pH 2, respectively. Greatest dissociation of individual caseins from the micelle occurred at pH 2.0. These serum caseins appeared in a form of fairly small soluble aggregates mainly consisting of α_S- and β-caseins. The composition of aggregates varied with applied shear, indicating orthokinetic aggregation and fragmentation.