Antimicrobial effect of pressurized carbon dioxide on Staphylococcus aureus in broth and milk

Studies were carried out to assess the use of high pressure CO2 treatment to inhibit Staphylococcus aureus in broth and raw cow's milk at 25 degrees C. Two phases in the survival curves were observed. The early stage was characterized by a slow rate of decrease in number of S. aureus; this rate increased sharply at the later stage. Staphylococcus aureus suspended in broth was completely inactivated after CO2 treatment at 7 MPa for 100 min and 8 MPa for 60 min. The sterilization effects of CO2 on both S. aureus and aerobic bacteria were observed at 14.6 MPa for 5 h and 9 MPa for 2 h in whole and skim milk, respectively. Staphylococcus aureus and aerobic bacteria were more difficult to inactivate when they were suspended in whole milk that may have protected the cell from penetration by CO2. Reduction rates of S. aureus and aerobic bacteria were sensitive to pressure, exposure time and the suspending medium. (C) 1997 Academic Press Limited.