## 3 Results and Discussion
### 3.6. Dough Rheological Properties during Heating  
#### 3.6.1. Protein Weakening  
The quadratic model describing C2 torque variation during protein weakening related to mechanical shear and temperature constraint is presented in Equation (9):  
\[\text{C2 }=0.4934\ +0.0145\cdot\text{X}_{1}-0.0267\cdot\text{X}_{2}\ +0.0071\cdot\text{X}_{1}\cdot\text{X}_{2}\ -0.0063\cdot\text{X}_{1}^{2}\ +0.0152\cdot\text{X}_{2}^{2} \tag{9}\]  
The regression model was statistically significant at \(p<0.005\) and fitted the experimental data for C2, showing a high coefficient of determination (\(R^{2}=0.82\)). It was found that particle size and QF level had a highly significant linear effect (\(p<0.05\) and \(p<0.005\)) on C2. The results showed an increase of C2 as the particle size increased and a decrease of C2 when QF addition increased (Figure 2a). The decrease of C2 can be explained by the lower water availability in the dough system due to the fact that the water absorption capacity of dough increases when the QF addition level increases, or it may be related to gluten dilution or to the activity intensification of proteolytic enzymes. C2 torque decreased with particle size reduction, especially in the case of small particle sizes, and may be linked either to a release of water molecules in dough or to the presence of a high content of proteins and the quinoa flour interfering with the protein unfolding. An increase of protein content in medium particle size, followed by small particle size, compared to large particles was observed (Table 2). Therefore, the balance between protein and starch from quinoa-wheat composite flour could play an essential role for dough consistency, particularly the amylose to amylopectin ratio.  
The protein network strength under increased heating, represented by the difference between torques C1 and C2 (C1-2), indicated that the quadratic model (Equation (10) was statistically significant at \(p<0.01\), and fitted adequately the experimental results of C1-2 with a high coefficient of determination (\(R^{2}=0.78\)).  
\[\text{C1-2 }=0.4934\ +0.0145\cdot\text{X}_{1}-0.0267\cdot\text{X}_{2}\ +0.0071\cdot\text{X}_{1}\cdot\text{X}_{2}\ -0.0063\cdot\text{X}_{1}^{2}\ +0.0152\cdot\text{X}_{2}^{2} \tag{10}\]  
The linear effect of particle size and level of QF addition on C1-2 was significant (\(p<0.05\) and \(p<0.005\)), while the interaction and quadratic effects of particle size and QF addition in wheat flour were not significant (\(p>0.05\)).  
It can be seen from Figure 2b that increasing the concentration of QF increased the C1-2 torque but increasing the particle size led to a decrease in C1-2. This decrease in C1-2 could be due mainly to the particles' composition. As observed from Table 2, high carbohydrate content was found in the large particle size with a low level of proteins, compared to the medium and small fractions. With respect to the combined effect between particle size and QF addition level on protein network strength, it was observed that the protein network became weaker under increased heating. The addition of QF caused a decrease of protein weakening speed with temperature rise. This is probably due to the changes in protein network structure which favor the enzymatic attack resulting from less compact proteins and, therefore, increased speed of protein weakening at higher temperature. The protein network decrease may be related with increased dough proteolytic activity, the enzyme having an optimal activity within the temperature range of this Mixolab stage. This result could also be also associated with the area-specific surface of quinoa starch, that is larger than for wheat starches and makes them more sensitive to hydrolysis by \(\alpha\)-amylase than wheat starch [76].