## Materials and Methods
### Experimental Design and Statistical Analysis  
In order to analyze the simultaneous effects of the KCl and NaCl amounts on the rheological properties of the wheat flour dough, the response surfaces methodology (RSM) was used. RSM has important application in the design, development and formulation of new products, to optimize the formulations factors [23; 24; 25] or to determine the optimum conditions for the process [26], showing the effect of the factors on the responses. Results optimization by the RSM method involved three main steps: the statistical design of the experiment, determination of the mathematical model coefficients and finally, prediction of the responses and checking the adequacy of the mathematical model within the design of the experiment (DOE) using the Design Expert software, trial version 12 (Stat-Ease, Inc., Minneapolis, MN, USA). For this study, two independent variables were chosen as follows: the influence of the variations of the potassium chloride amount (\(A=X_{1}\)) and sodium chloride (\(B=X_{2}\)) on the rheological parameters (dependent variables) of wheat flour dough. The experimental designs, with the real and coded values of the independent variables, are shown in Table 1.  
The rheological parameters determined by the Farinograph were WA--water absorption (\(Y_{1}\)); DT--development time (\(Y_{2}\)); ST--stability of dough (\(Y_{3}\)); DS--degree of softening (\(Y_{4}\)). The rheological parameters determined to Extensograph were: E--Energy (\(Y_{5}\)); R\({}_{50}\)--resistance to extension up to 50 mm (\(Y_{6}\)); R\({}_{\text{max}}\)--maximum resistance (\(Y_{7}\)); R/E--(\(Y_{8}\)). Moreover, the Falling Number index values (\(Y_{9}\)) have been determined. The rheological parameters determined by the Amylograph were T\({}_{\text{g}}\)--gelatinization temperature (\(Y_{10}\)); PV\({}_{\text{max}}\)--peak viscosity (\(Y_{11}\)); T\({}_{\text{max}}\)--temperature at peak viscosity (\(Y_{12}\)), H'm--height under constraint of dough at maximum development time (\(Y_{13}\)), VT--total volume of CO\({}_{2}\) produced during fermentation (\(Y_{14}\)), VR--volume of the gas retained in the dough at \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Run**} & \multicolumn{3}{c}{**Real Value**} & \multicolumn{2}{c}{**Coded Value**} \\ \cline{2-5}  & **KCl 1 (g/100 g)** & **NaCl 1 (g/100 g)** & **X1** & **X2** \\ \hline
2 & 1.5 & 0.3 & 1 & \(-\)1 \\
3 & 0.3 & 1.5 & \(-\)1 & 1 \\
4 & 0.9 & 0.9 & 0 & 0 \\
5 & 0.9 & 0.9 & 0 & 0 \\
6 & 0.9 & 0.9 & 0 & 0 \\
7 & 1.5 & 0.9 & 1 & 0 \\
8 & 0.9 & 0.9 & 0 & 0 \\
9 & 1.5 & 1.5 & 1 & 1 \\
10 & 0.9 & 1.5 & 0 & 1 \\
11 & 0.9 & 0.9 & 0 & 0 \\
12 & 0.9 & 0.3 & 0 & \(-\)1 \\
13 & 0.3 & 0.9 & \(-\)1 & 0 \\ \hline \hline \end{tabular} \({}^{1}\) KCl—potassium chloride; NaCl—sodium chloride.  
\end{table} 
Table 1: Real and coded values of independent variables used in the experimental design. the end of the test (\(Y_{15}\)) and CR--retention coefficient (\(Y_{16}\)). In order to minimize the measurement errors of the experimental data, the rheological values obtained for the wheat flour samples with different levels of KCl and NaCl addition according to our experimental design were carried out twice. In the statistical processing, their average values were used. The predicted responses of the system (\(Y_{1}\)... \({}_{\rm n}\)) (Equation (1)) in factorial screening experiments have been defined by a mathematical model:  
\[Y=f(X_{1},X_{2})=\beta_{o}+\sum_{i=1}^{n}\beta_{i}\cdot X_{i}+\sum_{i=1}^{n-1} \sum_{j=i+1}^{n}\beta_{ij}\cdot X_{i}\cdot X_{j}+\sum_{i=1}^{n}\beta_{ii}\cdot X _{i}^{2}+\varepsilon \tag{1}\]  
where \(\beta_{o}\) is the constant coefficient; \(\beta_{i}\) is the linear coefficient; \(\beta_{ij}\) is the interaction coefficient; \(\beta_{ii}\) is the quadratic coefficient; \(n\) is the number of factors studied and optimized in the experiment; \(X_{i}\) and \(X_{j}\) are the coded values of the independent variables and \(\varepsilon\) is the residual associated with the experiment.