## 3 Results and Discussion
### 3.6. Dough Rheological Properties during Heating
#### 3.6.3 Hot Starch Stability Gel  
The stability of hot-formed starch gel or cooking stability is represented by C4 torque. A quadratic regression equation (Equation (13)) was fitted to predict the effect of particle size and added QF level in wheat flour on the variation of C4 (Figure 4a).  
\[\text{C4 }=1.67\ +0.0079\text{-}\,\text{X}_{1}-0.2385\text{-}\,\text{X}_{2}\ +0.0130\text{-}\,\text{X}_{1}\cdot\text{X}_{2}\ -0.367\text{-}\,\text{X}_{1}^{2}\ +0.0074\text{-}\,\text{X}_{2}^{2} \tag{13}\]  
The regression model obtained was very good because the value of the coefficient of determination (\(R^{2}\)) was high and close to 1 (0.98), which indicated that 98% of total variation was explained by the model and only 2% of the total variation was unexplained. The effects of the formulation factor of QF added in wheat flour on the C4 torque showed a highly significant (\(p<0.0001\)) decrease with the QF level increase. The relationship with particle size decrease effect was not significant (\(p>0.05\)). The stability of hot-formed starch gel can be related to the stability of the already broken starch granules under heating ([PERSON] et al., 2016) [78]. The heating process at high temperature led to a decrease of viscosity associated with paste resistance to disintegration at high temperature, the lowest C4 value (\(1.39\ \text{N}\cdot\text{m}\)) being obtained for large particle sizes at a level of 20% QF added to wheat flour. For all formulations, the C4 torque had lower values compared to the control. The decrease of C4 torque with the amount of quinoa flour added can be explained by its high content of soluble fiber, mainly in small particle sizes, which can bind water by hydrogen bonds leading to a decrease of available water for the starch granules. On the other hand, [PERSON] et al. (2019) [28] showed that the low amylose content of quinoa seeds can lead to a more fluid gel formation without such a defined three-dimensional structure, contributing to a decrease in C4 torque.  
The difference of the points C3-4 was significantly affected by particle size and QF addition level in wheat flour at \(p<0.01\) and \(p<0.0001\), respectively. The regression model obtained (Equation (14)) fitted to the experimental results of the difference between torques C3-4 showed a high coefficient of determination (\(R^{2}=0.97\)), and indicated that the model explained 97% of the observed data variation.  
\[\text{C3-4 }=0.1860+0.0318\text{-}\,\text{X}_{1}+0.1295\text{-}\,\text{X}_{2}\ +0.0366\cdot\text{X}_{1}\cdot\text{X}_{2}+0.0144\text{-}\,\text{X}_{1}^{2}\ -0.015\text{-}\,\text{X}_{2}^{2} \tag{14}\]  
Figure 4: Response surface graph for combined effects of quinoa flour particle size and level added in refined wheat flour on Mixolab parameters during cooking stage: (a) C4 torque (C4) and (b) difference between torques C3 and C4 (C3–4).  
Figure 4b show the response surface graph for the combined effect of particle size and QF level addition in wheat flour on C3-4. It can be seen that as the particle size and QF level increased in samples, C3-4 increased.  
All the samples with QF addition had higher values of C3-4 compared to the control sample, depending on the particle size, even if the quinoa flour did not add amylase to the dough system. An increase of C3-4 could be associated with reduced gel stability when hot and may be due to starch damage.