In the conditions of HP treatment (500 MPa; max. 10.5 °C), CO2 is in subcritical state, i.e. under CO2 critical point (Tc = 31.1 °C, Pc = 7.38 MPa) and in liquid phase, whereas O2 is in supercritical state (Tc = −118.6 °C; Pc = 5,043 MPa) with properties of both liquid and gaseous oxygen (Amanatidou et al., 2000). Thus in the pressure treatment conditions, it seems that the physical state of both CO2 and O2 results that neither O2 nor CO2 can enter nor be released from the package during pressure treatment, especially since the pressure was transmitted through the use of water in direct contact with packages