A novel approach for characterisation of stabilising bonds in milk protein deposit layers on microfiltration membranes

The gel formation mechanism of low-pressure casein gels during the filtration of skim milk remains unknown this far. We investigated the prevailing bond types in this gel and correlated these findings with deposit layer properties and filtration performance. At high pH and low transmembrane pressure, calcium bridges predominated among the bond types stabilising the deposit layer gel. However, there were less calcium bridges present than within or between casein micelles in skim milk. With a decreasing amount of calcium bridges at low pH and higher transmembrane pressures, the deposit layer turned into a dense and mushy gel, which impaired solvent and solute permeability. Additionally, ionic and hydrogen bonds, as well as disulphide bonds, were formed between the highly concentrated deposited proteins during gelation. Hydrophobic interactions played a negligible role. We concluded that intramicellar calcium bridges are associated with a voluminous micelle and a stable gel backbone, which benefits filtration efficiency.