Investigating the effect of diluents and fat globules on the size measurement of casein micelles by dynamic light scattering

Abstract

The hydrodynamic size of casein micelles was examined using dynamic light scattering (DLS). Four types of diluents [ultrafiltration (UF) permeate, lactose-free simulated milk ultrafiltrate (SMUF), calcium imidazole buffer, and deionised water] were compared in their effect on the stability of casein micelles. Results of dilution series and kinetic size measurements revealed that both UF permeate and lactose-free SMUF enable size measurements that are hardly affected by the required dilution step, whereas a calcium imidazole buffer containing 10 mm CaCl2 only could provide accurate sizing results within a short time after dilution. The contribution of residual fat globules to the particle size distribution was negligible in skim milk. For semi-skimmed milk, the size of the casein micelles could be estimated by subtracting the contribution of the fat droplets (obtained upon dilution in a casein dissolving solution) from the raw DLS data (as obtained upon dilution in milk ultrafiltrate).