CO2-assisted high pressure processing on inactivation of Escherichia coli and Staphylococcus aureus

CO2-assisted high pressure processing was termed as CO2-HPP, and the inactivation of Escherichia coli and Staphylococcus aureus in liquid samples were treated by CO2-HPP in this study. When CO2 made up 20% of the total volume, it exhibited assisted inactivation of E. coli and S. aureus in phosphate buffered saline (PBS, pH 7.0) under HPP. Twenty percent CO2-300 MPa/3 min induced 1.0 and 2.5 more log units reduction of E. coli and S. aureus than 300 MPa/3 min, respectively. Both mid-exponential and stationary phase cells of E. coli and S. aureus showed higher sensitivity to CO2-HPP than HPP. However, the two microbes showed different inactivation behavior in real food of cucumber juice (pH 6.6) and apple juice (pH 4.3), and CO2-HPP was more suitable for S. aureus than E. coli in the two juices. As compared with HPP, CO2-HPP showed more severe damage on morphology and intracellular structure of E. coli and S. aureus cells through transmission electron microscopy (TEM), scanning electron microscopy (SEM), and flow cytometer microscopy (FCM), including appearance of collapsed cells, cell disruption, and more holes on cell membrane, membrane permeability, and strength of cytoplasm aggregation, which were probably due to the penetration, explosion, and acidification of CO2 under HPP. The CO2-assisted inactivation of bacteria subject to HPP has the potential application in food industry, especially for liquid food.