Processing and protein-fractionation characteristics of different polymeric membranes during filtration of skim milk at refrigeration temperatures

Serum protein concentrates (SPCs) were generated from reconstituted skim milk (3.2% protein) using lab-scale tangential-flow filtration at 3-4°C. The influence of membrane type on process performance (e.g., permeate flux) and protein-enrichment (e.g., protein profile) was assessed with polyvinylidene-difluoride membranes (0.1μm and 0.45μm pore-size), and a polyethersulfone membrane (1000kDa cut-off). The 1000kDa membrane exhibited the highest starting flux (6.7Lm^-2h^-1), followed by the 0.1μm (5.4Lm^-2h^-1) and 0.45μm (4.8Lm^-2h^-1) membranes. Flux decreased by >40% during filtration with the 1000kDa and 0.1μm membranes, while the decrease was lower (<20%) with the 0.45μm membrane. β-Casein comprised >97% of casein in SPCs from the 0.1μm and 1000kDa membranes. SPCs from the 0.45μm membrane had higher β-casein:α_s-casein ratios than the feed and higher levels of minor whey proteins (e.g., lactoferrin) relative to the other SPCs.