## 3 Results
### Evolution of Microbial Growth of OD-Treated Cherry Tomato and Spinach-Based RTE Products  
#### 3.2.1 OD-Treated Tomato-Based RTE Product  
The evolution of microbial growth for the OD-treated tomato-based RTE product with a storage time at all storage temperatures studied is presented in Figure 4a-c. The similar growth profile observed between the three substrates tested reveal that yeasts and molds are the dominant spoilage microflora for the tomato-based product. The dominant microorganisms in fruits (including tomatoes) are yeasts and molds. According to microbiological criteria recommendations, the maximum limits are \(1\times 10^{3}\) CFU/g for yeasts and molds and \(1\times 10^{5}\) (or \(1\times 10^{6}\)) CFU/g for aerobic mesophiles [43; 44]. The yeast and molds are undesirable in food, because they are able to produce a wide variety of enzymes, which cause the deterioration of food, impairing the sensory characteristics of the product. Moreover, many yeasts and molds can produce toxic metabolites in food, when the total count of these microorganisms is more than \(10^{6}\) CFU/g.  
Figure 3: Apparent moisture equilibrium curves at 25 \({}^{\circ}\)C for (**a**) OD-treated spinach, (**b**) peanuts and (**c**) OD-treated and air-dried cheese. The dashed lines represent the fitting of the GAB model to the experimental data.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Ingredient**} & \multirow{2}{*}{**Initial \(a_{uv}\)**} & \multirow{2}{*}{**Equilibrium \(a_{uv}\)**} & \multicolumn{2}{c}{**GAB Model Parameters**} & \multicolumn{1}{c}{**Predicted Equilibrium**} \\  & & & \(W_{m}\) (g/g) & \(C\) (-) & \(K\) (-) & \(a_{uv}\) (GAB) \\ \hline
**OD-treated spinach** & 0.930 \(\pm\) 0.003 a & & 0.883 \(\pm\) 0.011 a & 12.4 \(\pm\) 0.9 a & 0.884 \(\pm\) 0.003 a & \\
**OD-treated and air-dried cheese** & 0.533 \(\pm\) 0.002 b & 0.754 \(\pm\) 0.002 & 0.116 \(\pm\) 0.008 b & 4.04 \(\pm\) 0.3 b & 0.939 \(\pm\) 0.002 b & 0.758 \(\pm\) 0.003 \\
**Peanuts** & 0.431 \(\pm\) 0.002 c & & 0.031 \(\pm\) 0.001 c & 27.5 \(\pm\) 1.3 c & 0.944 \(\pm\) 0.003 b & \\ \hline \hline \end{tabular} Mean value \(\pm\) standard deviation. Different superscript letters in the same column indicate significant differences between means as calculated using [PERSON]’s multiple range test for a significance level of \(p=0.05\).  
\end{table}
Table 3: Water activity characteristics of the raw materials for the OD-treated spinach-based RTE product before mixing and at equilibrium. The predicted equilibrium value results from the water mass balances combined with the fitting of the GAB equation to the experimental data.  
In this study, microbial growth remains under a measurable level from approximately 10 to 40 days depending on the storage temperature, after which it rapidly increases. This can be attributed to the unfavorable growth conditions present within the OD-treated tomato-based product.  
The evolution of microbial growth (total viable counts) was mathematically modeled using the Gompertz model and the exponential rate constant (\(\mu_{m}\)) and lag phase (\(\lambda\)) were calculated (Table 4). The dependence of the Gompertz model parameters on storage temperature was modeled using the Arrhenius equation and the activation energy (\(E_{a}\)) was determined. The reduction in storage temperature from 20 to 4 \({}^{\circ}\)C led to a significant reduction in the exponential growth rate up to 95%. Additionally, the lag phase was increased up to approximately 70 d leading to a significant delay of microbial growth.  
Figure 4: Evolution of microbial load of the tomato-based composite product with storage time for all storage temperatures studied (4, 8, 12, 20 \({}^{\circ}\)C): (**a**) total viable counts, (**b**) total molds (**c**) yeasts and molds. Dashed lines represent the fitting of the Gompertz model to the experimental data.