I have noticed Vinegar listed in the ingredient lists for some types of bread? What is its function?

Vinegar is an acidity regulator, which is used to increase the acidity of the dough. Vinegar should be added at 0.6-1.5% of flour weight. Vinegar can be added for taste but it is primarily added to discourage the growth of mould, rope and bacteria. If too much acidity regulator is added it will suppress yeast activity meaning more yeast needs to be added or longer rising times are required.