Nonthermal inactivation of Escherichia coli K-12 on spinach leaves, using dense phase carbon dioxide

While the use of some chemical sanitizers is approved for inactivation of microbes on the surfaces of fruits and vegetables, these compounds often degrade product quality with limited improvement in product safety. The application of dense phase carbon dioxide (DPCD, or high-pressure CO2) is a nonthermal process for inactivation of foodborne pathogens inoculated into various juices and model solutions. In this work, DPCD was evaluated for its potential to inactivate Escherichia coli K-12 inoculated on fresh spinach leaves. Inoculated leaves were exposed for up to 40 min to DPCD at a subcritical condition (5 MPa, 40 degrees C) and two supercritical conditions (7.5 and 10 MPa, 40 degrees C) at a flow rate of 50 g of CO2/min. E. coli K-12 populations were reduced to nondetectable levels (approximately 5-log reduction) using supercritical treatment conditions at exposure times as short as 10 min; efficacy of DPCD at the subcritical state was limited. This research demonstrates that DPCD has potential as a pasteurization technology for application to leafy green vegetables, although issues with discoloration and other quality measures will need more extensive evaluations.