Which gas makes Orange juice bottles swell?
I can't imagine the gas was anything except $\ce{CO2}$ formed by the action of microorganisms contaminating the orange juice.  They degrade the organic components of the juice to power their metabolisms, and produce carbon dioxide as a byproduct.  

A common contaminant of pasteurized fruit juice is a genus of bacteria called Alicyclobacillus, but this paper says that Alicyclobacillus bacteria do not cause bottle swelling and do cause a medicinal smell.

By searching Google for ["bottle swelling" "orange juice"], I found an English-language abstract of a thesis from China which implies that the culprit could be a yeast.