Contributions from microstructural changes to the rheological behavior of casein dispersions during drying
In several applications, a protein such as casein in dispersion form, undergo multiple processing steps including drying. In this work, the rheological and microstructural features of drying casein dispersions were studied in comparison with that of equal concentrations of as prepared dispersions without drying. The microstructure of casein micelles is affected by drying due to the conformational composition changes in the secondary structures such as α-helix, β -sheets, turns and random struc- tures of the protein. Theoretical predictions using rheological data demonstrate that these changes affect the packing of casein micelles. During drying, casein dispersions start to show prominent shear thinning above 20 wt% along with the prevalence of α-helices and β -sheets. In comparison, direct dispersions show different microstructural features, and therefore different rheological response. A detailed analysis showed that alkalinity of the dispersing medium is the crucial factor controlling the microstructural changes and hence the rheology.