A laboratory investigation of the anhydrous milkfat fractionation using a membrane technique

Anhydrous milkfat (AMF) exhibits a broad melting point range (−40 to 60 °C) which can be separated into fractions of different and narrow melting point ranges using membrane technology. In this study, five different hydrophobic polymeric membranes (three composite membranes in the nanofiltration (NF) category, i.e. MWCO (300–400 Da) and (700–1000 Da), and two membranes in the ultrafiltration (UF) category, i.e. polysulfone MWCO 10 kDa and PVDF MWCO 30 kDa, were evaluated for AMF fractionation in a stirred and heated cell, in a batch mode filtration. The effect of different operating conditions of pressures (200, 300, and 400 psi at constant temperature 55 °C), fractionating temperatures (40, 30, 23, 20, 17, 13.5, and 10 °C at the optimum pressure (300 psi)), and stirring speeds (50–600 rpm) were investigated. The fractionation was confirmed by thermal profile analysis and solid fat contents (SFC) for both, the permeate fat and the rejected fat using differential scanning calorimetry (DSC). The qualities of milkfat fractions have been assessed using ATR-FTIR spectrophotometer. For an in depth investigation, Raman microscopy and scanning electron microscopy images and spectrum were recorded. The results indicate that at the optimum operating conditions of pressure (300 psi) and moderate stirring speeds (100 rpm), and at constant fractionation temperatures (30, 23, 20, 17, and 13.5 °C) carried out separately, using the UF membrane (30 kDa), AMF can be successfully fractionated. All fractions have the same quality of the intact fat. A mathematical model based on the experimental data have been derived to predict milkfat permeate (g min−1) at different operating temperatures (°C).