Inactivation of Escherichia coli (ATCC 4157) in diluted apple cider by dense-phase carbon dioxide

Dense-phase carbon dioxide (CO₂) treatments in a continuous flow through system were applied to apple cider to inactivate Escherichia coli (ATCC 4157). A response surface design with factors of the CO₂/product ratio (0, 70, and 140 g/kg), temperature (25, 35, and 45°C), and pressure (6.9, 27.6, and 48.3 MPa) were used. E. coli was very sensitive to dense CO ₂ treatment, with a more than 6-log reduction in treatments containing 70 and 140 g/kg CO₂, irrespective of temperature and pressure. The CO₂/product ratio was the most important factor affecting inactivation rate of E. coli. No effect of temperature and pressure was detected because of high sensitivity of the cells to dense CO₂. Dense CO₂ could be an alternative pasteurization treatment for apple cider. Further studies dealing with the organoleptic quality of the product are needed.