Ultrafiltration of skim milk: analysis of the streams, retentate and permeate, and membrane fouling.

Ultrafiltration (UF) of skim milk (SM) is one of the most widely used type of membrane processes in the dairy industry. It is of great importance to understand how operational variables can influence the efficiency of the process and the properties of the streams produced from SM. For this reason, this study focused on: (a) to evaluate membranes performances during UF process at different temperatures and (b) to determine physicochemical properties of the resulting SM streams namely retentates and permeates, with an emphasis on minerals partitioning. To tackle this, SM was concentrated to different volumetric concentration ratio (VCR; 1.0, 1.5, 2.0, 2.5 and 3.0) at three different temperatures (i.e., 10, 25 and 55°C). Samples of retentate and permeate were collected at different VCRs following physicochemical analysis. Permeates were evaluated for ionic calcium concentration ([Ca2+]), mineral profile, pH and conductivity. For retentates, [Ca2+], pH, particle size and zeta-potential were also measured for understating colloids of milk (i.e., casein micelles). In conjunction with this, membranes performances were also investigated, such as, flux variation and water permeability. The objective of this study was to investigate the influence of different temperatures and different VCRs during UF of milk on membrane performances and physicochemical properties of the produced streams (i.e., permeate and retentate). The findings of this work can be used and exploited for underpinning, optimising and standardising production of dairy-based products in which UF is a critical process (e.g., cheeses and dairy powders).