Enzymatic cleaning of inorganic ultrafiltration membranes used for whey protein fractionation

The aim of this work was to study the cleaning of inorganic membranes fouled by whey protein solutions using proteolytic enzymes. Tami® 150+4T membranes (Tami Industries, S.A., 26110 Nyons, France) of 400 kg/mol molecular weight cut-off (MWCO) and a ZrO2 filtering layer were selected to carry out the tests and Maxatase® XL (Genencor International, 2333 CN Leiden, The Netherlands) and P3-Ultrasil® 62 (Henkel Ibérica, S.A., 08025 Barcelona, Spain) were investigated as cleaning agents. Cleaning efficiency was observed to be a function of the operating conditions. The operating conditions studied were the pH of the cleaning solution, the enzymatic agent concentration and cleaning time. Very high cleaning efficiencies (close to 100%) were achieved in short operating times (20 min). The proteolytic enzymes were observed to adsorb onto the inorganic membrane used. However, enzyme-cleaned membranes gave better results than chemically-cleaned ones when used for whey protein fractionation: higher permeate flux was obtained, while selectivity remained practically the same. No peptides were detected in the retentate and permeate streams resulting from hydrolysis of proteins by the adsorbed enzyme. The possibility of reusing the enzyme solutions for consecutive cleaning steps was also studied. A 30% loss in activity was observed during each cleaning cycle, irrespective of the initial activity of the solution.