High carbon dioxide pressure inactivation kinetics of Escherichia coli in broth H. Karaman and O. Erkmen* The inactivation kinetics of Escherichia coli by high pressure carbon dioxide was investigated. Inacti- vation rates increased with increasing pressure (25, 50, 75 and 100 atm), temperature, and exposure time. Microbial inactivation followed ¢rst order reaction kinetics, with inactivation rates (k) and deci- mal reduction times (D) that varied from 0?0848 to 0?4717 min 71 and from 4?90 to 27? 46 min, respectively, at treatment temperatures (20, 30 and 408C). The inactivation rates of E. coli were described by the apparent activation volume (DV* ) and a ‘pressure z value’, and they were greatly dependent on both temperature and pressure. # 2001 Academic Press Introduction There is currently increased interest in the inactivation of micro-organisms in growth media and foods with high pressure carbon di- oxide (HPCD) as an alternative process to tra- ditional thermal methods (Daniels et al. 1985, Hong and Pyun 1999,Wei et al. 1991). HPCD treatment a¡ects biological systems by causing protein denaturation, lipid phase changes, and rupture of cell walls and membranes (Ballestra et al. 1996, Daniels et al. 1985). The presence of Escherichia coli in foods such as meat, ¢sh, and milk is an indicator of fecal contamination (Adams and Moss 1995, Hitch- ins et al. 1992). Outbreaks of diarrhoea, gastro- enteritis, and haemolytic uremic syndrome with pathogenic varieties of E. coli have been reported (Ballestra et al. 1996, CDC 1997, Hitchins et al. 1992, Sapers et al. 1999). Studies on the e¡ects of CO 2 under pressure on E. coli have been reported (Ballestra et al. 1996). For a broader use of HPCD in food processing, it is of special interest to determine the process condi- tions for pressure pasteurization (Erkmen 1997, Haas et al. 1989, Hong et al. 1997, Hong and Pyun 1999, Lin et al. 1994).To increase mi- crobial safety and assure microbial stability of foods processed by HPCD the pressure treat- ment must ensure a satisfactory reduction in the initial microbial counts, thus kinetic analy- sis and the pressure dependence of microbial inactivation rates are needed. The purpose of this research was to investigate the HPCD in- activation kinetics of E. coli in nutrient broth at various temperatures and pressures. Inacti- vation was described by k (inactivation rate), D (time at a speci¢c pressure required to reduce the viable population by 90%), D V* (activation volume of the reaction), and z (the pressure in- crement needed to reduce the D-value by a factor of 10) values. ORIGINAL ARTICLE *Corresponding author. Fax: 00-342-3601013 or 00 -342 -3601100; E-mail: erkmen@gantep.edu.tr Received: 14 February 2000 Department of Food Engineering, Faculty of Engineering, University of Gaziantep, 27310 Gaziantep, Turkey 0740 - 0020/01/010011 + 06 $35.00/0 # 2001 Academic Press Food Microbiology, 2001, 18, 11^16 doi:10.1006/fmic.2000.0371 Available online at http://www.idealibrary.com on