Influence of Processing Temperature on Membrane Performance and Characteristics of Process Streams Generated during Ultrafiltration of Skim Milk

The effects of processing temperature on filtration performance and characteristics of retentates and permeates produced during ultrafiltration (UF) of skim milk at 5, 20, and 50^◦C were investigated. The results indicate that despite higher flux at 50^◦C, UF under these conditions resulted in greater fouling and rapid flux decline in comparison with 5 and 20^◦C. The average casein micelle diameter was higher in retentate produced at 5 and 20^◦C. The retentate analysed at 5^◦C displayed higher viscosity and shear thinning behaviour as compared to retentate analysed at 20 and 50^◦C. Greater permeation of calcium and phosphorus was observed at 5 and 20^◦C in comparison with 50^◦C, which was attributed to the inverse relationship between temperature and solubility of colloidal calcium phosphate. Permeation of α-lactalbumin was observed at all processing temperatures, with permeation of β-lactoglobulin also evident during UF at 50^◦C. All UF retentates were shown to have plasmin activity, while lower activity was measured in retentate produced at 5^◦C. The findings revealed that UF processing temperature influences the physicochemical, rheological, and biochemical properties of, and thereby govern the resulting quality and functionality of, retentate-and permeate-based dairy ingredients.