Structure of milk protein deposits formed by casein micelles and β-lactoglobulin during frontal microfiltration

Frontal microfiltration and grazing incidence small angle X-ray scattering (GISAXS) are used to investigate how β-lactoglobulin (β-Lg) influences the deposit structure of casein micelles (CM). Filtration experiments show that the mean specific deposit resistance decreases with increasing concentration of β-Lg in the suspensions of CM. GISAXS is used to probe surface-near structures of deposits on a nano-meter scale. A core–shell model used to compute the scattering from CM shows agreement with measurements on films prepared by spin-coating on silicon wafers. The core of CM becomes more compact as a result of preferential binding of β-Lg on the micellar surface. Scattering functions of deposits prepared by filtration on micro-sieves show power-law behavior characteristic for mass-fractal structure. This structure consists of dense packed CM with interconnected β-Lg molecules on the surface. The resulting network of CM is porous and explains the reduced mean specific deposit resistance, as well as the increased permeate flow, in the presence of β-Lg.