Mathematical Model to Describe the Fates of Campylobacter jejuni on Raw Beef Liver

Introduction: Campylobacter spp. have been isolated from fresh meats such as poultry and beef, and usually cause campylobacteriosis by cross-contamination. However, if the products are eaten raw, the probability of the foodborne illness could be increased, especially for raw beef offal such as liver in certain countries.

Purpose: The objective of this study was to evaluate the fate of Campylobacter jejuni in raw beef liver with predictive models.

Methods: Raw beef liver was purchased from a wet market in S. Korea, and cut into 25-g portions. A mixture (0.1 ml) of C. jejuni strains ATCC33560 and NCTC11168 was inoculated into samples to obtain 6-7 log CFU/g, and the samples stored aerobically at 4°C, 10°C, 15°C, 25°C, and 30°C. C. jejuni cell counts in samples were then enumerated on modified CCDA-Preston, and these results were used to develop a primary model (Weibull model) to calculate Delta (time required for first decimal reduction) and p (the shape of curves). Delta were further analyzed with a secondary model (Davey model) as a function of storage temperature. The predicted data were compared with observed data, and root mean square error (RMSE) was calculated to evaluate the accuracy of the model prediction.

Results: C. jejuni cell counts were not changed at 4°C during storage, but dramatically decreased (P<0.05) at 10°C, 15°C, 25°C, and 30°C. The Delta values from the primary model were 1,344 h for 4°C, 157.5 h for 10°C, 54.2 h for 15°C, 22.7 h for 25°C, and 2.2 h for 30°C. Also, no differences in p values among temperatures were observed. The secondary model well-described the temperature effect on Delta with 0.842 of R². RMSE with 0.859 suggested that the accuracy of model performance was acceptable.

Significance: This result indicates that the developed model should be useful in describing the fate of C. jejuni in raw beef liver.