Fractionation of casein micelles and minor proteins by microfiltration in diafiltration mode. Study of the transmission and yield of the immunoglobulins IgG, IgA and IgM

There is little information concerning the fractionation by microfiltration (MF) of casein micelles and immunoglobulins plus other minor whey proteins with ceramic gradient membranes. The order of transmission was α-lactalbumin (α-La, 2.3 nm)> β-lactoglobulin (β-Lg; 4.2 nm)>IgG (10.7 nm)> lactoperoxidase (8.2 nm)> IgA (18.1 nm)> IgM (23.8 nm)> lactoferrine > blood serum albumin (7.8 nm), irrespective of the applied transmembrane pressure (0.6–3 bar) and equal to 55% > 50% > 47% > 41%>39% > 32% > 22% > 19%. Including preconcentration, it was possible to obtain 90% of the initial IgG, IgA and IgM within 85, 119, and 160 min, based on 1 m2 of membrane area and 50 L of skim milk volume. The long-term process exposure at 50 °C did not affect α-La and IgG but β-Lg (3–5% denaturation), which, however, was selectively retained by the MF. In conclusion, MF is not only suitable for fractionation of the major whey proteins and caseins, but also for the minor and far bigger immunoglobulins.