Nonthermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with gas-liquid porous metal contractor

Authors: Yuk, Hyun-Gyun; Geveke, David; Zhang, Howard

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2008
Publication Date: 1/20/2009
Citation: Yuk, H., Geveke, D.J., Zhang, H.Q. 2009. Nonthermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with gas-liquid porous metal contractor. Food Control. 20:847-851.

Interpretive Summary: The gas carbon dioxide (CO2) at moderate pressures (1100 psig) and at 31.1C becomes a supercritical fluid that readily kills bacteria. Several CO2 pilot-plant systems have been developed for liquid food processing; however there has been limited commercialization partially due to expensive operating costs. A recently developed supercritical continuous pilot-plant scale system using a gas-liquid contactor is more cost-effective than previous systems because it was designed to operate at a relatively low pressure. This study evaluated the effect of this new system on killing Escherichia coli K12 in a model food. Results showed that the kill rates improved at high CO2 concentrations and temperatures. Almost complete kill of E. coli was obtained at all tested temperatures (34, 38, and 42C). Storage tests after processing with supercritical CO2 showed that the number of cells decreased further at refrigeration temperature but increased at room temperature after 7 days. This work shows that this new supercritical carbon dioxide system is effective for liquid food processing.

Technical Abstract: This study evaluated the effectiveness of a supercritical carbon dioxide (SCCO2) system, with a gas-liquid CO2 contactor, for reducing Escherichia coli K12 in diluted buffered peptone water. 0.1% (w/v) buffered peptone water inoculated with E. coli K12 was processed using the SCCO2 system at CO2 concentrations of 3.1 – 9.5 wt %, outlet temperatures of 34, 38, and 42C, 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 microbial reduction. A maximum reduction of 5.8-log was obtained at 8.2% CO2 and 42C. To achieve a 5 log reduction of E. coli K12 in 0.1% buffered peptone water, minimum CO2 concentrations of 9.5, 5.5, and 5.3% were needed at 34, 38, and 42C, respectively. Further reductions of cells were observed after storage for 7 days at 4C. But storage at 25C increased the number of viable cells to 8-log cfu/ml after 7 days. This study showed the potential of the pilot scale SCCO2 system for microbial inactivation in liquid food.