Impact of stabilizing agents of commercial enzyme incorporated in formulated detergents on the cleaning of skim milk ultrafiltration membrane

PES/PVP membranes are widely used at industrial scale for skim milk ultrafiltration aiming at protein content standardization. Membranes are systematically fouled by proteins which are removed twice a day using formulated detergents among which enzymatic detergents often appear to be an eco-friendly solution. In this study, proteases called subtilisins, are selected and incorporated into a detergent formulation whose only variable was the source of subtilisin. Since liquid enzymes are commercially available in stabilized form, this allows to focus on the role of stabilizing agents on cleaning performance, even at very low concentrations. The selected UF membrane (HFK-131, Koch) has been fouled by skim milk at 50°C. Then, the cleaning efficiency of the prototype detergents was evaluated at 50°C from the residual protein quantified on membrane by ATR-FTIR. With equivalent enzymatic activity, detergents based on each one of the three selected enzyme sources, removed at least 95% of the proteins present at start evidencing the high cleaning efficiency. Simultaneously, the water flux recovery post-cleaning ranged from 1.9 to 3.8 requiring detailed and complex analysis to interpret this value greater than 1. Aiming at such understanding, a de-formulation approach was undertaken, combined with complementary ATR-FTIR characterization of membranes at every step. The discussion provides an explanation of the WFR behaviour likely associated with the variation in membrane hydrophilicity resulting to detergent ingredient adsorption. Besides the role of one given surfactant of the formulation, the impact of enzyme stabilizers was also demonstrated with possible synergetic effects with other ingredients.