Manufacture of high-solids milk protein concentrate retentate using plate-and-frame membrane filtration system at low and high temperatures

In the typical milk protein concentrate (MPC) manufacturing process, skim milk is ultrafiltered using a spiral-wound membrane to produce MPC80 with ∼20% total solids (TS) and 80% total protein on a DM basis. However, improving the production efficiency by achieving higher solids in the retentate has been a challenge when using spiral-wound membranes due to the limitation of operating pressure. We attempted flat-sheet UF membrane in a plate-and-frame (PF) module to concentrate the MPC further and achieve better production efficiency. Three replicates of ultrafiltered skim milk (feed) from spiral-wound UF membrane were concentrated in 3 different PF settings, including PF at 22°C (PF22), PF at 50°C for medium solids (PF50MS), and PF at 50°C for high solids (PF50HS). Hence, there were total 4 treatments: feed, PF22, PF50MS, and PF50HS. Filtration was carried out until the pressure drop reached 900 kPa for PF22 and PF50HS. For the PF50MS, the filtration was stopped when the TS achieved close to 30%. The average permeate flux and final TS were significantly higher for the treatments conducted at 50°C compared with 22°C with permeate fluxes of 8.76, 10.50, and 11.18 Lm^-2h^-1 and TS of 26.83, 29.92, and 34.24%, respectively, for the PF22, PF50MS, and PF50HS treatments. The apparent viscosity of the final retentates was 577; 1,513; and 12,805 cP at a constant shear rate of 100 s^-1 for the PF22, PF50MS, and PF50HS treatments, respectively. Standard plate count increased in the high-temperature PF retentates; however, the level was below the acceptable limit as described in the USDA standards for fluid milk. This study determined that PF temperature is an important parameter for improving the filtration performance of MPC. The study establishes guidelines for increasing TS and protein levels in dairy foods production.