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 (SCCO(2)) 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 SCCO(2) system at CO(2) concentrations of 0-10% (wt.%, g CO(2)/100g product), outlet temperatures of 34, 38, and 42 degrees C, a system pressure of 7.6 MPa, and a flow rate of 1L/min. Increased CO(2) concentrations and temperatures significantly (P<0.05) enhanced the bactericidal effect, resulting in a maximum reduction of 7.31 log CFU/mL at 8% CO(2) and 42 degrees C. A response surface model indicated that minimum CO(2) concentrations of 9.9% at 34 degrees C, 7.4% at 38 degrees C, and 5.4% at 42 degrees 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 SCCO(2) processing. At a processing condition of 8% and 38 degrees 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 SCCO(2) processed apple cider was not observed during storage for 28 days at 4, 8, and 20 degrees C. Thus this study showed the potential of SCCO(2) processing with a gas-liquid porous metal contactor for the nonthermal pasteurization of apple cider.