Molecular mechanism of casein-chitosan fouling during microfiltration

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 & alpha;S1- and & beta;-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.