The first thing that’s important to know is that there is an odd international convention on the naming of MPC products. If the protein is 85% or higher, it is stated on a “dry matter” basis (DMB) whereas products with protein levels of 80 or below are stated on an “as is” or “on powder” basis, so MPC-80 is 80% protein as is and MPI-85 is 85% protein DMB.
If you think of any type of food product, it consists of some level of moisture – as you can never remove 100% of the moisture when drying an ingredient. For example, white rice has an average moisture content of about 12%. If you tried to dry it further, you would have some burning or unpleasant changes to the rice. You can measure the level of any macro or micro nutrient (such as protein) as a percentage of the product itself (the rice itself, which contains some moisture), or you can measure the protein as a percentage of the dry matter only. The same is true with milk protein concentrate and isolate.
To move from product to dry matter basis, you simply remove the weight of the water and calculate the percentage on the dry matter. So, if you have 100 grams of MPI-85 powder, it typically contains 5.3 grams of water and 82.0 grams of protein. This is the “as is protein” because it’s the amount of protein in the powder. The percentage of protein on a dry matter basis will be higher. To calculate the protein on a dry matter basis, you remove the water, so 100 g powder – 5.3 g water = 94.7 grams of dry matter. You convert from “as is” to DMB by taking the percentage protein on a DMB basis and dividing by the new percentage of dry product: % protein DMB = as is protein / (1- % water). In this case, % protein DMB = 0.82/(1-.053) = 0.866. Note that this isn’t a perfect calculation because all the analyses are run independently and not all numbers are listed with the same number of significant figures.