A Mass and Energy Balance for Fractionation of Serum Proteins from Skim Milk by Ceramic Microfiltration

It is possible to separate serum components, particularly proteins, in milk using microfiltration (MF); however, the partition dynamics for large globular proteins is challenging from an efficiency perspective. This study assessed the partitioning of serum proteins, when skim milk was microfiltered using a 0.1 μm graded permeability ceramic membrane, from a mass balance and energy utilisation perspective. The MF was carried out at 50°C at a volume concentration factor (VCF) of 3 with two sequential diafiltration (DF) steps. A mass balance focused on dry matter, crude protein, and true protein yielded recoveries of 99.5, 94.9, and 95.3%, respectively. However, an accurate mass balance relative to colloidal and serum protein (SP) contents, as determined by analysis of nitrogen fractions, in the retentate and permeate streams relative to the feed was not achieved. The overall percentage SP removal for the three-step MF and DF process was found to be 90.14 and 50.63%, when considering non-casein nitrogen determination, in the permeate and retentate streams, respectively. This observation is similar to discrepancies reported in the literature relative to casein/whey separation, highlighting potential errors associated with quantifying nitrogen fractions in processed streams using standard methodologies designed for nitrogen fractions determination in raw milk. The corresponding energy required for the initial VCF 3 filtration step followed by the two diafiltration stages was 13.1, 13.7 and 20.6 kWh/kg of SP removed, respectively. Demonstrating the dynamic relationship between SP protein partition and yield relative to diafiltrant utilisation and its subsequent impact on energy consumption per kg SP partitioned.<br>