*2.2. Downstream Process*

NF processes were performed using a polyethersulfone spiral membrane with a nominal cut-off of 150–200 Da, respectively, with a total filtering area of 0.3 m<sup>2</sup> (Fluxa Filtri, Milano, Italy). The system used for the membrane process was a UF-NF system equipped with a 10 L volume steel tank, pressure gauges on the inlet and retentate lines, and a thermostatic bath to keep the temperature constant (Idea 3 Engineering, Lessona, Italy). The whey fraction provided by the dairy factory had been ultrafiltered in site on 20 kDa polyethersulfone membranes with a filtering surface of about 40–50 m<sup>2</sup> and flux of 2500–3000 L/h. The concentration factor reported was 13–14 fold, on the basis of 10,000 L used at the inlet for each treatment. In this study, 10 L of the permeate of the abovementioned UF on 20 KDa were nanofiltered and concentrated. All recovered fractions were characterized by analyzing lactate, lactic acid and total proteins as described in the following paragraph.
