## 3 Results and Discussion
### Effect of Operating Parameters on Responses
#### 3.1.1 Effect of Single Parameters  
For both responses, \(p\)-values (\(<\)0.05) for all single factors (A, B and C) confirmed the significant effect of feeding capacity, conveyor speed, and thermal oil flow rate. Moreover, the value of each corresponding coefficient in the Equation (4.1) and (4.2) is positive which clearly indicates the positive effects of all individual factors on MC and L*. Therefore, it is concluded that MC was increased with an increase in the value of each operating parameter and vice versa.  
It is evident from Table 3 that the thermal oil flow rate, with the highest F-value (708.78), has the most significant effect on MC, followed by conveyor speed and feeding capacity. These findings reveal that the change in MC is more sensitive to temperature rather than travel time and quantity of groundnut in the roasting cylinder within the given experimental ranges of operating parameters. The inside temperature of the roasting cylinder was controlled by varying the thermal oil flow rate in the system. At higher flow rate, lesser heat was absorbed and transferred from the heat receiver to the bottom of the roasting cylinder, therefore, a lower temperature was obtained for the roasting of groundnut kernels and vice versa. It was due to the fact that heat absorption and desorption rates depend upon the specific heat capacity of HTF, which increases at lower flow rates and decreases at higher flow rates [29]. Therefore, lowest final MC was observed with minimum flow rate of thermal oil. Furthermore, MC was also influenced by the roasting time that was dependent on the conveyor speed. The greater conveyor speed reduced the time of travel inside the roasting cylinder that resulted in less heat transfer to the groundnut kernels. Thus, slightly higher percentage of MC and little quantity of unroasted kernels were recorded as also confirmed by the other researchers [13]. A lesser impact of feeding capacity was seen on MC in comparison with other operating parameters because even though at maximum feeding capacity, adequate heat is available for effective roasting [30].  
For L* response (Table 4), it was determined that the thermal oil flow rate has the most significant effect on the color change of groundnuts. Due to increase in temperature inside the roasting cylinder, MC started to reduce that led to modifications in the microstructure of the groundnut kernels followed by several chemical changes. The browning of kernels by heat application occurred due to Maillard reactions and somewhat from caramelization [19]. Lowest thermal oil flow rate and conveyor speed yielded in a higher temperature and longer time for roasting, respectively that produced a darker color of the final product and exhibited lower values of L* whereas lighter color presented a light roast condition with higher values of L* [20; 31]. Beside the thermal oil flow rate and conveyor speed,  
Figure 2: Relationship between predicted and observed values of (**a**) moisture contents (MC) and (**b**) Hunter Labs colorimeter color value (L*).  
feeding capacity impacted the L* to a lesser extent as the heat was well distributed in the roasting cylinder even at maximum feeding capacity [30].