Ion exchange

The most important job that emulsifying salts do is to enact an ion exchange in the cheese mixture, whereby monovalent sodium and potassium ions replace the polyvalent calcium ions.
That triggers a removal of the bridges that bind the calcium ions inside the casein, i.e. the milk protein, and that hold the protein together. The milk protein can now unfold and develops properties similar to an emulsifier to create a bond between the fat and water phases. That’s the basic requirement for the production of processed cheese.