What is the purpose of adding milk proteins to yogurt?

People add Milk Protein Concentrate (MPC) and/or Whey Protein Concentrate (WPC) to yogurt as functional ingredients. They are sometimes erroneously referred to as “stabilizers”. Prior to MPC being plentiful, it was noted that adding a protein product to yogurt milk did improve yogurt gel stability (shelf life). The higher the viscosity of the protein in water, the better it is at stabilizing…because high viscosity proteins will bind more water. That is why sodium caseinate works the best as a yogurt stabilizer. Sodium caseinate binds much water, thereby extending yogurt gel stability before syneresis and loss of gel structure. This may not seem like a big deal, but it is. Yogurt manufacturers strive continually to extend shelf life. In their efforts to gain longer shelf life, formulators add gums, gelatins, pectins, and starches (all known as stabilizers) to bind water. Regulations in different countries limit how much of these stabilizers a yogurt manufacturer can add. Stirred curd yogurt manufacturers need more stabilizing/viscosity building in their yogurts than the legal maximum levels of stabilizers will sometimes provide. That is when yogurt manufacturers look to milk proteins to perform a stabilizer type of function in yogurt. Initially, yogurt manufacturers turned to WPC for extra stability. With the advent of MPC manufacture, MPC became a preferred functional ingredient in yogurt.