Role of milk constituents on critical conditions and deposit structure in skimmilk microfiltration (0.1 μm)

Crossflow microfiltration (0.1 μm) of skimmed milk is widely used in the dairy industry to separate casein micelles from soluble proteins. The accumulated matter at the membrane surface turns into an irreversible deposit in critical hydrodynamic conditions (CHC) (J/τw)crit that irreversibly alters filtration performance. The aim of this work was to identify the milk constituents responsible for CHC and to evaluate the role of constituents (casein micelles, soluble proteins, minerals) on the microfiltration performance and deposit structure. An original methodology of filtration based on step-by-step τw variation at constant flux was used with dairy fluids of variable and controlled composition. Casein micelles were shown to be the milk constituents responsible for the apparition of the CHC, creating an irreversible deposit at the membrane surface. Soluble proteins had no effect on the set-up of the CHC, but their presence in milk increased by 20% the irreversible fouling. The presence of the mineral aqueous phase of milk played a role in CHC set-up and irreversible fouling. Calcium ions are supposed to create bonds in the deposit between the membrane and the micelles and between micelles themselves.