There is very little difference between an MPC and an MPI—If both are truly filtered products…ultrafiltration, microfiltration, etc. A truly filtered MPI (90% protein dry basis—about 86% protein “as is” basis) contains a higher protein content than an MPC 80 (80% protein minimum “as is” basis) or MPC 85 (82.5% protein minimum “as is” basis).
An MPI will have a higher protein content (anywhere from 3.5% to 6%) because it contains that much less lactose (MPI usually contains about 1% to 2% lactose). In most food ingredient functional applications, there is little discernible difference between a truly filtered MPI and an MPC 80 or 85. Most companies purchase MPI because they desire a “lactose free” label declaration.
There are, however, numerous Milk Protein Isolates (MPI) that are manufactured in much the same manner as casein/caseinates. They are nothing like a true MPC or a truly filtered MPI. These types of proteins are also called Milk Protein Isolates.
These types of MPIs are usually manufactured by precipitating casein and/or casein/whey protein aggregates from skim milk and washing the curd to purify the protein—much the same process as casein/caseinate manufacture. In fact, most of the Milk Protein Isolates on the market today are not much different from a caseinate with a little bit of whey protein mixed in. In actual fact, there is no legal definition anywhere in the world for a Milk Protein Isolate.
The name was derived from proposed Food Codex Alimentarius Guidelines for protein products wherein a protein concentrate was defined as a powder having a protein content between 40% and 89% and a protein isolate powder would have a minimum protein content of 90%. Under these proposed guidelines, the protein content is a “dry basis” protein content, meaning that an MPI powder need only have an “as is” protein content of about 86% to be called an “isolate.”
There are many manufacturers of MPI in other countries who blend caseinates with whey proteins and call the blends MPI. The majority of MPIs available today (those that are manufactured with a precipitation step in their processing) do not accurately reflect the FDA’s opinion of a milk protein—having the same proteins as they are naturally found in milk and in the same ratios as they are naturally found in milk.
The majority of MPIs for sale today do not contain all of the whey proteins as found in milk and certainly not in the ratios as naturally found in milk. Be very careful to ask questions about the protein that you are buying. Was it manufactured solely from a filtration process or was precipitation and alkali added anywhere during the processing?