## 2 Materials and Methods
### Experimental Design  
The \"Control Units\" were utilized to assess the pH, water activity (a\({}_{\rm w}\)), and NaCl content (%) values of the cheese samples and to evaluate the existing \"microbial flora\"--mesophilic aerobic count and lactic acid bacteria (Lab)--present in the food on \"Day 0\" and on the end of the shelf life--\"Day End\". These units served to evaluate potential effects arising from changes in the actual composition of the food, which practically results in \"identical\" physicochemical conditions to those in the inoculated \"Test Unit\" samples.  
On \"Day 0\", for three of the eight \"Test Units\" inoculated with \(Lm\) samples of each cheese (full-fat and light), \(Lm\) enumeration was performed. The remaining inoculated \"Test Unit\" samples were stored at 5 \({}^{\circ}\)C for 24 days to simulate the conditions at the production and transportation levels. The subsequent \(Lm\) enumeration was performed after 35 days of storage at 7 \({}^{\circ}\)C, after 49 days of storage at 7 \({}^{\circ}\)C, and after 57 days of storage at 7 \({}^{\circ}\)C to simulate storage conditions at the retail level. Finally, the remaining samples were tested after another 17 days of storage at 10 \({}^{\circ}\)C, on the last day of the shelf life on the \"Day End\" (181 st day), to mimic storage conditions at the consumer level.  
An additional \"Control Unit\" sample (\(n=1\)) was dedicated to monitoring the storage temperatures of the test samples studied. A thermal data logger (Elitech RC-5) was placed inside a designated \"Control Unit\" sample within the same incubator, as close as possible to the \"Test Unit\" samples, to continuously record temperature data throughout the experiment. Also, on the two above \"Control Unit\" samples, gas atmosphere monitoring measurements were performed, two measurements per Batch on \"Day 0\" and two on \"Day End\".  
On \"Day 0\", from each Batch, five (\(n=5\)) \"Food Control Samples\"--the samples without any inoculation--were analyzed to confirm the absence of \(Lm\). Five samples (\(n=5\)) of each Batch were tested on \"Day 0\" for pH and a\({}_{\rm w}\), to ensure the uniformity and representativeness of the samples received from each Batch. Also, the pH, a\({}_{\rm w}\), NaCl content (%), and fat content (%) values in these samples were tested, as well as the microbial flora naturally present in the product. Furthermore, on the above \"Food Control Samples\", gas atmosphere monitoring measurements were performed, five measurements (\(n=5\)) on \"Day 0\" and two (\(n=2\)) on \"Day End\".  
All microbiological criteria analyses were performed following ISO methods [59; 60; 61; 62]. Fat content and salt concentration were determined in the aqueous phase, and the water activity (a\({}_{\rm w}\)) and pH values were determined using AOAC procedures [63].  
All the procedures mentioned above are summarized in Table 1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Units** & **Type of Analysis** & **Number of Units and Day of Analysis per Batch \({}^{*}\)** \\ \hline \multirow{3}{*}{**Test Units**} & \multirow{3}{*}{Enumeration of \(Lm\)} & \multirow{3}{*}{8} & 3 Test Units on “Day 0”, 1 Test Unit \\  & & & on each of 4 intermediate dates, and \\  & & & 1 Test Unit on “Day End” \\ \hline \multirow{6}{*}{**Food Control Samples**} & Detection of \(Lm\) & & \\ \cline{2-4}  & Measurement of & & \\ \cline{1-1}  & physicochemical characteristics & & \\ \cline{1-1}  & Enumeration of the & 5 & 5 on “Day 0” \\ \cline{1-1}  & associated microflora & & \\ \cline{1-1} \cline{2-4}  & MAP measurement & & \\ \cline{1-1} \cline{2-4}  & MAP measurement & 2 & 2 on “Day End” \\ \hline \hline \end{tabular}
\end{table}
Table 1: The protocol and the number of units that were analyzed per Batch \({}^{*}\) for the determination of \(Lm\) growth in Greek light and full-fat semi-hard sliced cheeses, packed under a modified atmosphere (MAP).