Effect of temperature on the performance of plate-and-frame filtration during milk protein concentrate manufacture

In the typical milk protein concentrate (MPC) manufacturing process skim milk is ultrafiltered using spiral wound membrane to produce MPC with 20% total solids (TS) and more than 80% total protein (TP) based on solids. This MPC is then further concentrated before spray drying using reverse osmosis or nanofiltration. In this study we had attempted to concentrate MPC using a plate-and-frame filtration (PF) system instead of spiral wound system. Three replicates of MPC80 having TS 20.01, 19.70 and 20.65% from the ultrafiltration of skim milk were concentrated in a PF system fitted with flat sheet membranes (Alfa Laval M37; surface area 3.3 m2 with a 10 kDa molecular weight cut-off). Three different PF settings were utilized including: PF at 22°C (PF22); PF at 50°C for medium solids (PF50MS); PF at 50°C for high solids (PF50HS). Filtration was continued until the transmembrane pressure difference was 9 bar for PF22 and PF50HS. For the PF50MS, filtration was stopped when the TS achieved was 30%. The average flux, final TS and TP/TS ratio were 8.76, 10.50 and 11.18 L/m2 hr, 26.83, 29.92 and 34.24% and 0.83, 0.88 and 0.87 respectively for the PF22, PF50MS and PF50HS treatments. The average flux, final TS and TP/TS ratio were significantly (P \u3c 0.05) higher for the treatments conducted at 50°C as compared with 22°C. The viscosity of the retentates corresponded to the final TS and was 577, 1513 and 12805 cP for the PF22, PF50MS and PF50HS treatments, respectively. The permeate from the PF50HS treatment had significantly (P \u3c 0.05) higher solids and TP as compared with the other treatments. The standard plate count (SPC) of the retentate before drying was significantly (P \u3c 0.05) higher for the treatments at 50°C and was 3.54 to 4.41, 5.17 and 5.28 log10cfu/g for the PF22, PF50MS and PF50HS treatments, respectively. The loose and tapped density of MPC powders after spray drying were significantly (P \u3c 0.05) lower for the PF50MS and PF50HS treatments. This study determined that, increasing the PF temperature improves filtration performance and the level of TS achieved but also increase the SPC count of the final retentate