Efficacy of supercritical carbon dioxide for nonthermal inactivation of Escherichia coli K12 in apple cider

This study evaluated the efficacy of a supercritical carbon dioxide (SCCO2) system with a gas–liquid porous metal contactor for eliminating Escherichia coli K12 in apple cider. Pasteurized, preservative-free apple cider was inoculated with E. coli K12 and processed using the SCCO2 system at CO2 concentrations of 0–10% (wt.%, g CO2/100 g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Increased CO2 concentrations and temperatures significantly (P < 0.05) enhanced the bactericidal effect, resulting in a maximum reduction of 7.31 log CFU/mL at 8% CO2 and 42 °C. A response surface model indicated that minimum CO2 concentrations of 9.9% at 34 °C, 7.4% at 38 °C, and 5.4% at 42 °C are needed to achieve a 5-log reduction of E. coli K12 in apple cider. SEM observations showed morphological changes in the cell envelope after SCCO2 processing. At a processing condition of 8% and 38 °C, the reduction of E. coli was 6.03 log and the sublethal injury of the survivors was 84%. The regrowth or survival of E. coli in SCCO2 processed apple cider was not observed during storage for 28 days at 4, 8, and 20 °C. Thus this study showed the potential of SCCO2 processing with a gas–liquid porous metal contactor for the nonthermal pasteurization of apple cider.