I am NOT a scientist, but I found this discussion interesting.

It is, in short, about the optimal pH of fermented dough and wild yeast cultures. The interesting points are: (1) wild yeast cultures maintain a lower pH than the internal pH of fresh yeast cells; (2) the longer dough ferments, the lower its pH drops; and (3)at some point, the pH will drop so low that the structure of the dough will break down and the yeast will not be able to produce enough carbon dioxide to leaven the bread.

I know that the yeast eat the sugars in the flour to produce carbon dioxide and, if given the chance, will eat enough of the sugars that the they no longer have sufficient fuel to produce carbon dioxide. Obviously something about this process changes the pH of the dough, as starter cultures (dough fermented over a long time) have a lower pH than fresh dough, with the only variable being fermentation (and, perhaps, the source of the yeast).

I don't take any measurements when I bake. I keep rough track of the fermentation times and don't measure the fermentation temperature, the size of the dough, or the internal temperature of the loaves after they are done baking. I barely keep track of my baker's percentages. So this pH stuff is interesting on a theoretical level, but probably won't impact my baking. It is interesting though and, if I would like, it gives me another set of variables to play with.