Charged ultrafiltration membranes increase the selectivity of whey protein separations.

Ultrafiltration is widely used to concentrate proteins, but fractionation of one protein from another is much less common. This study examined the use of positively charged membranes to increase the selectivity of ultrafiltration and allow the fractionation of proteins from cheese whey. By adding a positive charge to ultrafiltration membranes, and adjusting the solution pH, it was possible to permeate proteins having little or no charge, such as glycomacropeptide, and retain proteins having a positive charge. Placing a charge on the membrane increased the selectivity by over 600% compared to using an uncharged membrane. The data were fit using the stagnant film model that relates the observed sieving coefficient to membrane parameters such as the flux, mass transfer coefficient, and membrane Peclet number. The model was a useful tool for data analysis and for the scale up of membrane separations for whey protein fractionation.