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Effect of high pressure on inactivation of Escherichia coli in frozen suspension

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131595065,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Guangming Su, Minsheng Zhou, Jinsong He, Yong Yu, Songming Zhu
Keywords:   High pressure frozen phase transition inactivation Escherichia coli

Abstract. High pressure treatments (200-400MPa, holding 0-5 min) were performed in ambient temperature using samples of frozen and unfrozen suspension containing Escherichia coli (ATCC 25922). Samples (2 ml each, sealed in a plastic valve), were put in a cylindrical container to reduce the effect of heat transfer on sample temperature during pressure processing. Sample temperatures were monitored during pressure treatment using K-type thermocouples. E. coli was found to be more sensitive to pressure when inoculated in frozen suspension than in unfrozen suspension. The calculated D-values of E. coli destruction in unfrozen suspension were 9.64, 8.4, 5.2, 3.14 and 1.59 min at 200, 250, 300, 350 and 400 MPa, respectively, compared to 8.33, 6.47 and 2.59 min at 200, 250 and 300 MPa when inoculated in frozen suspension. Ice phase transition during pressure cycles was analyzed and more phase transitions existed at a higher pressure which resulted in a higher destruction rate of E. coli. During pressurization above 350 MPa, the temperature of frozen samples experienced the lowest point at -33oC followed by a quick increase to -20oC, the temperature decrease and quick change induced more ice phases that could cause mechanical damage to E. coli cell. This phenomenon was independent of the pressure holding time but the applied pressure. The results in the study shows the combined treatments of frozen and high pressure are more effective to inactivate E. coli than high pressure treatment alone due to the synergic effect of ice phase transition.

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