## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Batch**} & \multirow{2}{*}{**Day**} & \multirow{2}{*}{**Concentration** (Log CFU/g)**} & \multicolumn{2}{c}{**SD**} & \multirow{2}{*}{**Median**} & \multirow{2}{*}{**Growth Potential**} & **Highest \(\delta\)** \\  & & & **(Standard** & & & **(\(\delta\)) per Batch** & **among the** \\  & & & & & & **3  Batches** \\ \hline \multicolumn{2}{c}{**A**} \\ \hline \multirow{4}{*}{\(1\)} & & & 2.15 & & & & \\  & 0 & 2.18 & 0.02 & 2.15 & & \\  & & 2.15 & & & & 2.28\(-\)2.15 = 0.13 & \\  & 10 & 2.28 & 0.14 & 2.28 & & \\  & & 2.23 & & & & \\  & 0 & 2.3 & 0.09 & 2.23 & & \\  & & 2.11 & & & 2.63\(-\)2.23 = 0.40 & 0.40 \\  & & 2.08 & & & 2.63 & \\  & 10 & 2.63 & 0.48 & 2.63 & & \\  & & 3.04 & & & & \\  & & 2.10 & & & & \\  & 0 & 2.13 & 0.04 & 2.10 & & \\  & & 2.05 & & & 2.50\(-\)2.10 = 0.40 & \\  & & 2.50 & & & & \\  & 10 & 2.40 & 0.08 & 2.50 & & \\  & & 2.56 & & & & \\ \hline \multicolumn{2}{c}{**B**} \\ \hline \multirow{4}{*}{\(1\)} & & & 2.3 & & & & \\  & 0 & 2.28 & 0.14 & 2.28 & & \\  & & 2.04 & & & & \(<\)1\(-\)2.28 = \(>\)\(-\)1.28 & \\  & & \(<\)1 & & & & \\  & & 2.08 & & & & \\  & 0 & 2.63 & 0.48 & 2.63 & & \\  & & 3.04 & & & & 1.00\(-\)2.63 = \(-\)1.63 & \(-\)1.28 \\  & & 1.48 & & & & \\  & 70 & 1 &At day 0 of storage (that corresponds to the sampling day 10) the registered median concentrations of _L. monocytogenes_ were 2.28 Log CFU /g for batch 1, 2.63 Log CFU /g for batch 2 and 2.50 Log CFU /g for batch 3 (Table 2B). The growth potential of _L. monocytogenes_ was \(-\)1.28 Log CFU /g for batch 1 and 3 and \(-\)1.63 Log CFU /g for batch 2, therefore, concerning the storage time of spreadable salami, the \(\delta\) is \(-\)1.28 Log CFU/g. As reported for the production process, in the conservation time the calculated \(\delta\) is also lower than 0.5 Log CFU/g, confirming that the product is unsupportive of _Listeria_ growth [31]. Furthermore, in this phase, not only is the calculated \(\delta\) below the limit set by the reference document, but it is also represented by a negative value (\(<0\)), suggesting, therefore, that during the conservation time the hurdles applied to the spreadable salami are able to exert their action against the growth of _Listeria_, decreasing the pathogen concentration (Figure 1 and Table 2B). The growth curves of _L. monocytogenes_ in experimentally produced spreadable salami contaminated at the beginning of the production process and stored according to the abovementioned conditions were obtained by fitting the observed growth data using the DMFFit program (Figure 2). According to the Combase Predictor tool (part of the Modelling Toolbox, www.combase.cc) [42] in culture media with equivalent growth conditions of salami, a maximum _L. monocytogenes_ population of 8.51 log CFU/g was reached in about 625 h (26 days, data not shown). However, the fitted growth curves show that the pathogen concentration reached a maximum level of 2.43 log CFU/g and then the growth was suppressed (Figure 2), corroborating the results reported above concerning the definition of _Listeria_ growth potential. The DMFFit program was also used to calculate growth parameters for each condition tested (Table 3). The maximum specific growth rates (\(\mu\)max, 1/h) ranged from \(-\)0.0019 to \(-\)0.0013, while the latency phase (Lag) ranged from 776 to 1032 h. The lower asymptote was not reached at the end of the considered shelf life, therefore the final values for the three batches were not determined. The results of the fitting of observed growth data corroborate the outcomes of the challenge test. For each of the three growth curves, in fact, the value of \(\mu_{\text{max}}\) was negative, confirming that the growth of the targeted pathogen was suppressed in the food environment considered. As shown in Table 3, the latency phase (Lag) of the three fitted curves ranges from a minimum value of 32 days (780 h) to a maximum value of 42 days (1032 h) for batch 2 and 1, respectively.