Molecular mechanism of casein-chitosan fouling during microfiltration
Résumé
In this study, the casein-chitosan complexes were subjected to microfiltration. The filtration property was
analyzed, and the molecular mechanism of fouling was explained under different medium pH, casein-chitosan
ratios and ionic strength. Results suggest that a higher pH and more polysaccharide can slow down the
fouling growth rate, but a higher pH is unfavorable for long-term processing. Especially the effect of pH on the
process was far more significant than the others. At pH 2.8, most of amino acid residues combined with chitosan
to form the denser particles and to generate the gel consistency and yield stress. Thus, the severe fouling
resistance was caused by the tight gel layer stacked on membrane surface. At pH 6.8–7.8, the electrostatic
binding energy between casein and chitosan decreased. The complexes gel consistency and yield stress disappeared,
and the incompact network was formed. Thereby, the cake layer density and the fouling growth rate
were reduced. At pH 4.8, the amino acid residues of αS1- and β-casein bound to chitosan decreased. Although the
complex exhibited the gel consistency and yield stress, the microfiltration efficiency was improved due to the
decrease of binding sites. This work provides new evidences into understanding the membrane fouling
mechanism.