## 2 Materials and Methods
### Materials
The composition of retenate and permeate samples was analyzed using a MilkoScan(tm) FT2 infrared milk analyzer (Foss, Hillerod, Denmark) for process control. At the end of the MF run, the retenate and the permeate collected during the processing run were combined and sampled. The MF experiment was performed in three replicates. The MF retenate was subjected to DF twice, in order to produce native micellar casein concentrate with reduced serum protein (SP) content. The MF retenate (obtained in the first stage) was diluted by weight to 1\(\times\) CF by reverse osmosis (2 kg of pasteurized RO water per kg of the retenate, DF factor of 3), and it was used in the first DF process. The retenate was combined with water before heating to 50 \({}^{\circ}\)C, and it was processed in the MF system to achieve 3\(\times\) CF under identical conditions as in the first stage. The third and last MF stage (second DF) was identical to the second MF stage (first DF); the retenate from the second stage was diluted with RO water, and it was used as the feed. All retenates and permeates were collected, cooled, combined, and sampled [16]. The final MF retenate (liquid MCC) was spray-dried after cooling and storing overnight (4 \({}^{\circ}\)C). SP removed from milk by MF was further purified and concentrated by ultrafiltration to obtain SPC. Both MF permeates and the DF permeate from the first DF were cooled to 4 \({}^{\circ}\)C and stored overnight before SPC production. One day after MCC production, MF permeates and the DF permeate from the first DF were weighed, combined, heated to 50 \({}^{\circ}\)C, ultrafiltered (UF stage 1 with 5\(\times\) CF) and diafiltered (DF stage 2 at 8\(\times\) CF) to produce 60% liquid SPC. The final UF retenate (liquid SPC) was spray-dried after cooling and storing overnight (4 \({}^{\circ}\)C). The feed for the ultrafiltration process was fractionated in a pilot-scale UF system (continuous bleed-and-feed recirculation mode). The system was equipped with a semipermeable polyethylene(PES) spiral wound membrane (model: 3838 HFK-131, Koch Separation Solutions, Wilmington, MA, USA) with a nominal pore size of 10,000 Da and a surface area of 6.7 m\({}^{2}\). Ultrafiltration was carried out under the following conditions: feed temperature--around 50 \({}^{\circ}\)C; retenate inlet pressure--around 4.2 bar for UF and around 3.8 bar for DF, with no back pressure on the permeate side. At the beginning of the UF process, before the retenate and the permeate were redirected to the feed tank, approximately 10 to 15 L of the feed was collected and discarded to flush water out of the system. Next, the retenate and the permeate were returned to the feed vat, and retenate and permeate outlet valves were adjusted to the indicated CF values. Before DF, RO water was added to the UF retenate in an amount corresponding to the amount of permeate obtained during UF. When the desired CF was achieved, the permeate and retenate streams were directed to cooling and storage tanks. When the process was completed, the final UF retenate and permeate were combined and sampled for analysis in the MilkoScan(tm) FT2 infrared milk analyzer (Foss, Hillered, Denmark). The final MCC and SPC retenates were spray dried with a Production Minor Spray Dryer (Niro Atomizer, Seborg, Denmark). The feed was kept at or below 7 \({}^{\circ}\)C; the feed rate was approximately 15 kg/h; the inlet temperature was 180 \({}^{\circ}\)C and the outlet temperature was 80 \({}^{\circ}\)C. The dried product was collected, packaged in hermetically sealed plastic bags, and weighed after the run. Powder samples intended for physicochemical analyses were stored in a shaded place, at 21 \({}^{\circ}\)C [17].