Final answer:
The most likely deterioration of mayonnaise when heated is the separation of water and oil, due to the denaturing of egg proteins which act as emulsifiers.
Step-by-step explanation:
When an emulsion like mayonnaise is heated, the most likely deterioration that occurs is the separation of water and oil. Mayonnaise is an emulsion consisting of oil in vinegar stabilized by egg yolk components, which act as emulsifying agents.
Heating mayonnaise can disrupt this delicate balance causing the oil and vinegar to separate as the egg proteins that act as the emulsifier can denature with heat reducing their effectiveness. This process is different from protein precipitation or hydrolytic rancidity where proteins form insoluble aggregates or fats undergo oxidation and hydrolysis respectively and is also distinct from simple dehydration.