Bubbles in unopened store bought items?
1.Some companies when they pack would fill it with a air form of preservatives.

2.Other reason for the bubbles could also be simple air that was trapped when it was packed or sealed in the container or packet. And maybe the container/packet was shaken up a bit when dispatched, causing the air inside to move around in the product.

should have no effect on the product. Just trust the best before date. (Unless it tastes funny) :)