Milk protein concentrate (MPC) is produced from skim milk by a series of processes that includes ultrafiltration, evaporation and drying. MPC contains undenatured forms of both casein and whey protein. The level of protein, lactose and minerals present varies depending on the degree of protein concentration. Ultrafiltration determines the composition of the MPC while evaporation and drying are used to remove only water. The product also is pasteurized to eliminate potential pathogens in raw milk.
Ultrafiltration is a process that separates milk components according to their molecular size. During this process, milk passes across a membrane. Some of the lactose, minerals and water will cross through the membrane and become the permeate stream. Casein and whey proteins, because of their larger molecular size, will not be able to pass through the membrane. The proteins, along with the lactose and minerals that did not go into the permeate stream, will become the retentate stream. A diafiltration, or washing step, is required to get protein concentration greater than 65% in the final dried product. Diafiltration involves adding water to the retentate as it is being ultrafiltered to reduce product viscosity and further remove lactose and minerals.
Following UF, the retentate may be evaporated to increase the total solids in the processing stream, which helps in the drying process. The retentate then is spray-dried.
Currently, there is no standard of identity for MPC in the United States. Although ultrafiltration is the preferred method for extracting MPC, it also can be produced by precipitating the proteins out of milk or by dry-blending the milk proteins with other milk components. Depending on how MPC is produced, costs may vary and, more important, functionality may differ.
Commercially, MPCs are available in a range of protein levels, from 42% to 85%. Typical MPCs offered are MPC42, MPC70, MPC75, MPC80 and MPC85. As the protein content of MPCs increases, the lactose levels decrease. For example, MPC42 is 42% protein and 46% lactose. MPC80 contains 80% protein and 4.1% lactose. For comparison, skim milk powder contains about 35% protein and 52% lactose.
MPCs are white to light-cream-colored dry powders. They are best used within one year of receipt. Recommended storage is below 77°F and 65% relative humidity in a cool, odor-free, dry environment. If the product has been opened and resealed, it should be used within one month of opening.
Typical Composition of Milk Protein Concentrate (%)
MPC is used for its nutritional and functional properties. It is high in protein content (casein and whey protein) and contributes about 360 Kcal/100 g. Higher protein-containing MPCs can be low in carbohydrate content, containing minimal amounts of lactose. This high-protein, low-lactose ratio makes MPC an excellent ingredient for protein-fortified beverages and foods and low-carbohydrate foods. MPCs also retain a fair portion of calcium because it is bound to the casein.