It is well known that WPP will undergo Maillard Browning over storage time. This is because WPP contains the milk sugar, lactose, which is a well-known reducing sugar, along with free amino acids and short length, hydrolyzed protein peptides.
In the manufacture of cheese, protein hydrolysis occurs, leaving a remnant of free amino acids and small peptides that end up in WPP that results after filtration of the cheese whey to concentrate intact proteins. Because there are so many reactive nucleophilic amino acid groups in WPP, very little energy is required for the Maillard reaction to proceed. Therefore, the Maillard reaction can occur at ambient temperatures over time in WPP.
MPP is not as likely to undergo a Maillard reaction as is WPP. MPP also contains lactose but it does not contain as many free amino acids or hydrolyzed protein peptides as WPP because the process of filtering skim milk to make MPC does not cause protein hydrolysis to occur, as in cheese manufacturing. Therefore, the Maillard reaction does not proceed as easily with MPP. MPP will undergo Maillard reactions in applications where sufficient heat is introduced and sufficient time is allowed for the reaction to proceed. In general, however, it can be said that the Maillard reaction is less likely to occur when using MPP as an ingredient when compared to WPP.