Shear separation: a promising method for protein fractionation

摘要

Shear Separation is a method of separating macromolecules suspended in a fluid by inducing hydrodynamic forces that depend on size. The forces are produced in the laminar sub-layer of a turbulent shear boundary layer adjacent to a porous membrane. The suspended particles are lifted away from the porous membrane, against the drag of the permeate flow, by the viscous part of the shear stress. We have found that the transmission rate of a protein through the membrane depends on the shear rate, the permeate rate, the protein size, and the protein shape, even when the pore size of the membrane is substantially larger than the largest of the proteins. As a result, this is a size and shape dependent separation of the macromolecules. The membrane functions as a surface upon which an extremely high shear laminar sub-layer at the membrane surface may be generated. The effect has been demonstrated on the bench scale with clean mixtures of cytochrome C and bovine serum albumin. The separation can be observedwith membranes rated approximately 300 kg centre dot mol~(-1) molecular weight cut off (MWCO) or less. Using this technique, milk serum containing BSA and smaller proteins without fats, caseins or immunoglobulins has been produced from skimmed milk. Inaddition, the milk serum has been fractionated with transmission fractions of 18 percent for BSA, 33 percent for #beta#-lactoglobulin, and 62 percent for #alpha#-lactalbumin.