By using the newly modified method for the determination of the mean specific resistance during
cross-flow filtrations of milk a study was carried out, which allows an evaluation of the mean specific
fouling resistance as a function of pressure and colloidal interactions between casein micelles in the
deposit. Due to the extremely fast flux decline, when milk was used as a filtration fluid, milk was diluted
by protein free milk serum (10 kDa UF-permeate).
The speed of the deposit formation could thus be reduced. As shown in fig. 2, a dilution did not lead
to a significant change in deposit build up and thus resulted in an equivalent specific fouling resistance. A
dilution of 1:5 (milk: UF-permeate) gave the required speed reduction for gaining a sufficient amount of
data points (>>10) for the ln-linearization (4). Hence, this concentration was used for all experiments to
keep the casein concentration as close to the native concentration as possible. Fig. 2 shows, that an
increase in the pressure drop through the deposit layer increased the mean specific resistance for the
filtration of milk at native pH 6.8 as well as for a lower pH 5.9. During filtrations at reduced pH, the
pressure dependency was significantly higher. For a better visualization, trend lines based on e-functions
are used in the diagram.