## 4 Discussion
### Listeria monocytogenes Behavior  
The survival kinetics of _Listeria monocytogenes_ (_Lm_) from the initial inoculation (150 CFU/g) on \"Day 0\" to the designated \"Day End\" (Day 181) were evaluated in light and full-fat semi-hard sliced cheeses packaged under modified atmosphere packaging (MAP). Across all six Batches, a gradual decline in _Lm_ populations was observed, reaching significantly reduced levels by this study's endpoint.  
In light cheeses, the _Lm_ population decreased to a quantifiable presence below \(4.0\times 10^{1}\) CFU/g in all three Batches but did not achieve complete elimination. Similarly, in full-fat cheeses on \"Day 181\", _Lm_ counts were below 10 CFU/g in Batches 1 and 3. Batch 2 of the full-fat cheese exhibited _Lm_ levels below \(4.0\times 10^{1}\) CFU/g, again without reaching 0.  
A comparative analysis of _Lm_ behavior across the three Batches of light and the three Batches of full-fat semi-hard sliced cheese under MAP indicated that, within the parameters of this study, the fat content of the cheese matrix did not exert a significant influence on the reduction in _Lm_ populations, as similar trends were observed in both cheese types.  
Under the specific MAP conditions employed, _Lm_, as an aerobic and facultatively anaerobic microorganism, demonstrated a substantial reduction to very low levels in both cheese categories. However, complete eradication was not achieved, signifying its survival under these conditions.  
Based on these findings, Greek light and full-fat semi-hard sliced cheeses, packaged under MAP with a 6-month shelf life and stored under the conditions applied in this investigation, meet the criteria for \"Ready-to-Eat Food unable to support the growth of _Lm_\" and are classified under food safety category 1.3 of (EC) Regulation 2073/2005. Nevertheless, the persistent presence of _Lm_, albeit at low levels, at the end of the shelf life necessitates caution. Deviations from recommended storage conditions or compromised MAP integrity leading to an altered gaseous environment could potentially facilitate _Lm_ proliferation. The synergistic effects of reduced oxygen, elevated carbon dioxide and nitrogen concentrations, and refrigeration are known to extend the shelf life of food products while preserving quality and inhibiting spoilage.  
Considering the inherent complexities of sliced cheese production, encompassing multiple handling stages and MAP, post-pasteurization contamination with _Listeria monocytogenes_ remains a relevant concern. An initial contamination level of 150 CFU/g, while seemingly low, represents a plausible scenario given potential environmental exposure during the slicing and packaging processes. Despite the utilization of pasteurized milk and the inhibitory effects of MAP coupled with appropriate storage, the observed survival of _Listeria monocytogenes_, even at minimal concentrations, at the conclusion of the product's shelf life underscores the organism's resilience and the critical importance of rigorous hygiene protocols throughout the entire food processing chain.  
Although this study did not apply predictive microbial growth models, such tools, like those provided by ComBase, could be employed in future studies to simulate how varying NaCl concentrations in the aqueous phase influence the growth kinetics of relevant spoilage or pathogenic microorganisms. This approach would enhance risk assessment and shelf life predictions in high-fat cheeses such as feta.