Shelf life evaluation for ready-to-eat sliced uncured turkey breast and cured ham under probable storage conditions based on Listeria monocytogenes and psychrotroph growth

The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced uncured turkey breast and cured ham was studied under storage conditions that RTE foods are likely to encounter. Three product treatments studied were: (1) a control; (2) a formulation subjected to high pressure processing to reduce initial microbial load (HPP); (3) a formulation containing 2.0% potassium lactate and 0.2% sodium diacetate (PL/SD). After separate inoculation with individual L. monocytogenes ribotypes and packaging each treatment under air and vacuum, the packages were stored at 4, 8, or 12 °C and the counts of L. monocytogenes and psychrotrophic bacteria (PPC) were determined for several weeks. The Baranyi model was used to estimate lag times and growth rates. Significant effect of strain difference was noted in both sliced products (P < 0.05). In the absence of antimicrobials (HPP and control), the growth rate (GR) of L. monocytogenes strains increment from 4 to 8 °C and from 8 to 12 °C was approximately 10 and 2 fold, respectively. The addition of PL/SD was effective in restricting the growth of L. monocytogenes and PPC at 4 °C, but at 8 and 12 °C significant growth was observed (more than 100-fold increase) (P < 0.05). In PL/SD samples, vacuum packaging slowed down the onset and the rate of growth of L. monocytogenes at 12 °C in sliced ham and at 8 and 12 °C in sliced turkey breast. Generally, the time to increase by 2-logs was greater in control samples than as observed in HPP-treated samples. When antimicrobials were present, the current results showed that L. monocytogenes was able to grow more than 100-fold within the typical quality-based shelf life of 60 to 90 days at 8 and 12 °C. The findings of this study should be useful in setting the duration of a safety-based shelf life for RTE sliced meat and poultry foods.