What food products are dependent on microorganisms and why?

Everything. Microorganisms are essential for nitrogen fixation, so without them there would be no proteins, anywhere. So plants would grow, so nothing else would, either. Even if you got past that, ruminants depend on microorganisms to break down the coarse material they eat, so without them, no cows so no beef and no milk. If you mean this in a more specific sense of which ones directly use microorganisms in production, I can think of bread, which relies on yeast and certain cheeses, which use molds in their production.