Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/26/2003
Publication Date: 2/1/2004
Citation: Chen, H., Joerger, R.D., Hoover, D.G., Kingsley, D.H. 2004. Pressure inactivation kinetics of bacteriophage lambda ci 857. Journal of Food Protection. 67:505-511. Interpretive Summary: High pressure processing (HPP) has been shown to be effective for reducing bacterial contamination in foods. Preliminary work also indicates that HPP may be effective against water- and food-borne viruses. Identification of a virus surrogate for the purposes of routine experimentation and validation of commercial HPP processes could be of potential benefit to food scientists and industry. Lambda bacteriophage, a harmless virus infecting E.coli bacteria, has been evaluated as a model system for high pressure inactivation studies and as a potential surrogate for food-borne and water-borne viruses. Evaluation of extended-time lambda inactivation curves at 44,540 PSI (pounds per sq. inch) 51,965 PSI, and 59,390 PSI in tissue culture media and 2% reduced fat milk was performed. Results indicate that solutions with higher protein and fat content, such as milk, reduce the sensitivity of lambda bacteriophage to pressure-induced inactivation. As with curves observed for bacteria, most inactivation by HPP occurs within the first few minutes at a given pressure. At later times, the rate of inactivation slows dramatically. Fitting the observed inactivation curves to several inactivation model equations indicate that the Weibull model most closely matches observed values. Comparison with pressure inactivation curves of hepatitis A virus (HAV) indicates that lambda bacteriophage is somewhat more sensitive to pressure than HAV. Consequently, lambda bacteriophage is not deemed to be a suitable surrogate for HAV; however it may be suitable for other viruses.
Technical Abstract: Viability curves of bacteriophage lambda cI 857 inactivated by high hydrostatic pressure were obtained at three pressure levels (300, 350, and 400 MPa) in buffered media and ultra-high temperature 2%-reduced fat milk. Pressurization of bacteriophage lambda in buffered media at 300 MPa for 300 min, 350 MPa for 36 min, and 400 MPa for 8 min reduced the titer of bacteriophage lambda by 7.5, 6.7, and 7.7 log10, respectively. Pressurization of bacteriophage lambda in milk at 300 MPa for 400 min, 350 MPa for 80 min, and 400 MPa for 20 min reduced the titer of bacteriophage lambda by 5.4, 6.4, and 7.1 log10, respectively. Tailing was observed in all viability curves, indicating that the linear model was not adequate for describing these curves. Among the three nonlinear models studied, the Weibull and log-logistic models consistently produced best fits to all viability curves and the modified Gompertz model the poorest. Since there were no significant differences in the values of shape factor (n) for suspension medium buffer, we reduced the number of parameters in the Weibull model from two to one by setting n at the mean value. The simplified Weibull model produced a fit comparable to the full model. Additionally, the simplified Weibull model allowed predictions to be made at pressures different from the experimental pressures. Menstruum was found to significantly affect the pressure resistance of bacteriophage lambda. Comparison of pressure inactivation of hepatitis A virus and bacteriophage lambda indicated that bacteriophage lambda is more sensitive to pressure than hepatitis A virus in Dulbecco's Modified Eagle Medium with 10% fetal bovine sera.