There is described a packaging apparatus (1) for forming a plurality of sealed packages (2) from a tube (3) of a web of packaging material (4) which is continuously filled with a pourable product. The packaging apparatus comprises a delimiting element (37) arranged, in use, within the tube (3) and being designed to divide the tube (3), in use, into a first space (38) and a second space (39). The packaging apparatus (1) also comprises a sterile gas supply device (43) for pressurizing the isolation chamber and the second space (39) by means of a respectively a first flow of sterile gas and a second flow of sterile gas.