Two types of membrane filtration processes, namely ultrafiltration and microfiltration, are used for protein standardization in milk. While ultrafiltration is used to standardize the total protein, microfiltration is used to standardize the casein.
Using ultrafiltration, it is possible to concentrate raw or pasteurized whole or skim milk. Ultrafiltration of skim milk can produce different milk protein concentrate (MPC) and milk protein isolate (MPI) products with polymeric spiral membranes. Microfiltration of skim milk can produce casein concentrate with polymeric spiral membranes or ceramic membranes depending on the specific application.
The by-products (permeate stream) from ultrafiltration and microfiltration of milk are also valuable. The permeate stream from the ultrafiltration process is primarily lactose, and this stream is an ideal product for standardization of milk powders.
The permeate stream from the microfiltration process contains native whey proteins that can be further processed into higher value protein products such as whey protein isolate or other whey protein concentrates.