Modelling of Campylobacter survival in frozen chicken meat

Abstract

To model the survival kinetics of Campylobacter jejuni on frozen chicken meat. Three different types of chicken meat surface (skin, skinned muscle and cut muscle) were inoculated with stationary phase cells of C. jejuni (8 log(10) CFU cm(-2)) and frozen for 5 weeks at -20 degrees C. Bacterial numbers were determined weekly using two different methods of enumeration to quantify uninjured and injured cells. Analysis of variance of the results showed that the type of chicken surface and the method used to enumerate surviving cells were the most significant sources of variations in the numbers recovered (P < 0.0001), much more than the freezing time. To identify an appropriate model for the description of effects of freezing on survival over time, several models were fitted to the count data. Decay was found to be nonlinear. In general, survival was least on skin, better on skinned muscle and best on cut muscle. After 2 weeks, additional inactivation by freezing appeared to be negligible. Because of the variability of survival it was not possible to fit and select a general model useful for all the different surfaces types. The injured state of the cells leads to variability and the underestimation of bacterial survival. This is an essential factor for the assessment of Campylobacter-associated risk.