What each one does
Soy protein emulsifies strongly and sets into a firm gel on heating, which holds fat and gives slice integrity. Collagen binds water and converts to gelatin, which melts in the mouth and gives the juicy, yielding bite that a purely soy bound product lacks.
What decides it
What is failing. Fat separation and soft slices point to soy. A product that is firm but dry and rubbery points to collagen.
Where the obvious answer is wrong
The obvious answer when a product separates is more emulsifier. If the fat is separating because the meat protein was never extracted, adding soy masks a salt, phosphate or chopping problem that will return at the next raw material change.
