## 2 Materials and Methods
### Experimental Design  
A Box-Behnken design (BBD) was employed to determine the optimal conditions for osmotic dehydration process of strawberries. The design involved three factors at three levels (low (\(-\)1), medium (0), high (+1)), leading to a total of 15 experimental runs. Each experiment was conducted three times for accuracy. The independent variables investigated in the osmotic process were glycerol concentration in osmotic solution (40%, 50%, 60% \(w/w\)), immersion time (90 min, 180 min, 270 min), and temperature (30 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, 50 \({}^{\circ}\)C). These variables were selected based on their documented influence on osmotic dehydration, with specific studies indicating that glycerol concentrations between 40 and 60% significantly impact water loss and solid uptake in fruits and vegetables [3;25]; immersion times ranging from 90 to 270 min have been shown to optimize mass transfer during osmotic dehydration; and temperature ranges of 30-50 \({}^{\circ}\)C play a critical role in accelerating the dehydration process while preserving the product's quality [3; 25; 26; 27; 28; 29; 30; 31; 32]. The ratio of sample to osmotic solution was set to 1:8 (\(w/w\)), according to a series of preliminary experiments, where the ratio varied between 1:4 and 1:12, and was supported by literature findings to ensure sufficient interaction between the solution and the fruit [26; 33; 34]. The dependent variables, measured as responses, were WL and SG, which are critical indicators of dehydration efficiency and product quality in food processing [30]. All the experiments were performed in a randomized order to minimize the potential impact of uncontrolled factors and eliminate systematic errors. Three of the fifteen experiments were conducted with all factors at the medium (0) level to evaluate and confirm the model's precision by calculating the average and the standard deviation of these experiments. The coded values in correspondence with the real values of the procedure, and the 15 experimental conditions determined by the Box-Behnken design are presented in Tables 1 and 2, respectively. The OD factor ranges were selected based on values commonly reported in the literature, ensuring alignment with established research and maintaining relevance to practical applications [6; 20; 22]. While these ranges provide a robust framework for optimizing osmotic dehydration, it is acknowledged that exploring a wider range of variables might yield additional insights. However, the selected ranges were deemed appropriate for the objectives of this study, given the practical constraints of industrial applications, such as maintaining product quality and preventing texture or nutrient degradation at extreme conditions. The experimental data were analyzed using RSM to develop mathematical models for WL and SG. The design of the experiments and the analysis of the experimental data were conducted using the software Minitab (trial version 20.4, Minitab LLC, State College, PA, USA, 2021). The linear regression method of the polynomial model, consisting of 10 coefficients, was used to describe the relationship between the response variable (Y) and the independent variables (A, B, and C) as shown in Equation (1). In this model, Y represents the response variable (WL or SG). The term \(\beta_{0}\) denotes the estimated coefficient \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Osmotic Dehydration Factors** & \multicolumn{3}{c}{**Coded Values/Real Values**} \\ \hline Independent Variables & \(-1\) & 0 & 1 \\ \hline A: Glycerol Concentration (\% \(w/w\)) & 40 & 50 & 60 \\ B: Temperature (\({}^{\circ}\)C) & 30 & 40 & 50 \\ C: Immersion Time (min) & 90 & 180 & 270 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Actual and coded values of the investigated factors.