Process of removal of gases from the can prior sealing is called

The process of removal of gases from the can before the seal is called Exhausting.
It is the removal of dissolved gases from liquids, especially water or aqueous solutions. There are numerous methods for removing gases from liquids.
In canning the objective of exhausting containers is to remove air in the product so that the pressure inside the container, following heat treatment and cooling, will be less than atmospheric.