Submitted to: Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/4/2011
Publication Date: 5/11/2011
Citation: Sheen, S., Hwang, C., Juneja, V.K. 2011. Modeling the impact of chlorine on the behavior of Listeria monocytogenes on ready-to-eat meats. Food Microbiology. 28:1095-1100. Interpretive Summary: Chlorine is commonly used to sanitize processing equipment and utensils. Listeria monocytogenes may survive the treatment then contaminate food products. This study demonstrated the impact of chlorine (0 – 50 ppm) and temperature (4 – 16 degree C) on the Lm growth and survival behavior on ready-to-eat meat products. The higher chlorine concentration and lower temperature may significantly retard the Lm growth including longer lag time and slower growth rate. Models were developed to describe the Lm survival. These finding and models may enhance risk assessments for microbial safety as ready-to-eat meats.
Technical Abstract: Listeria monocytogenes (Lm) continues to pose a food safety hazard in ready-to-eat (RTE) meat due to potential cross-contamination. Chlorine is commonly used to sanitize processing equipment and utensils. However, Lm may survive the treatment and then contaminate food products. The objective of this study was to characterize the behavior of chlorine-exposed Lm on RTE ham stored at 4, 8 and 16 degree C. A two strain cocktail of Lm serotype 4b was pre-treated with chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto the surface of RTE ham to obtain an inoculum of about 3.0 log CFU/g. Inoculated ham samples were stored 4, 8, and 16 degree C, and Lm was enumerated periodically during the storage. The growth characteristics (lag time and growth rate) of Lm were estimated using the DMFit software. The results indicated that Lm growth was surpressed by the chlorine treatment. At 4 degree C, the lag time of Lm after exposure to 0 ppm of chlorine (4.2 days) was shorter than those exposed to 25 ppm (5.4 days) and 50 ppm (6.8 days). The lag time decreased with the increase of temperature, e.g., at 25 ppm, the lag times were 5.2, 3.8 and 2.6 days for 4, 8 and 16 degree C, respectively, and increased with the increase of chlorine concentration, e.g., at 16 degree C, the lag times were 1.2, 2.6 and 4.0 days for 0, 25 and 50 ppm, respectively. However, growth rate increased with increased temperature and decreased with increased chlorine concentration. The lag time and growth rate as a function of chlorine concentration and temperature can be described using a modified Ratkowsky model and a modified Zwietering model, respectively. The results showed that the growth of Lm on RTE ham was suppressed by pre-exposure to chlorine. The predictive models developed will contribute to microbial risk assessments of RTE meats.