Unless you can prove damage,

You hardly have a case to sue the store for compensation. When you bring the bread to the store, they may allow you to return it, but they would never admit it is their fault, just for legal reasons. You can also search the store's current inventory, if you can find more of the bread with mold, you can take pictures as evidence just in case damages do happen.

In any case, alerting public health department would help, well, the public, in case the store has repeated offense.