## 3 Results and Discussion
### Effect of Operating Parameters on Responses
#### 3.1.3 Interactive Effect of Parameters on Hunter Labs Colorimeter Color Value (L*)  
The interactive effect of feeding capacity and conveyor speed on the L* value of groundnuts was determined at the center level of the thermal oil flow rate (0.03 Ls\({}^{-1}\)) as shown in Figure 4a. A positive effect on L* is observed both by the conveyor speed and feeding capacity but the conveyor speed affects more significantly in comparison with feeding capacity. It is clear from the 3D surface plot that increasing the feeding capacity and conveyor speed to maximum levels resulted in brighter color value (L*) of groundnut kernels i.e., 58.34. The longer roasting time with minimum feeding capacity lowers the L* value to 45.51, thus producing a medium roast quality kernel. It is because a lower conveyor speed gives longer roasting time, which offers an opportunity for adequate heat transfer to groundnuts even at maximum feeding capacity. This result infers that prolonged roasting time produces dark roasted groundnuts, and vice versa, and in agreement with the findings of [35]. The investigations from [32] also revealed that the roasting time is the most effective parameter for promoting color changes in groundnuts during roasting at constant temperature and dark roast conditions can be attained with longer roasting time.  
Figure 4: _Cont_.  
At a constant conveyor speed of 1.0 rpm, the interactive effect of feeding capacity and thermal oil flow rate on the L* is represented in a 3D surface plot (Figure 4b). The L* value of groundnuts was decreased with decreasing the feeding capacity and thermal oil flow rate. The observed value of L* was 39.77 at minimum levels of feeding capacity and thermal oil flow rate and raised up to 59.72 with maximum feeding capacity and thermal oil flow rate. These low (39.77) and high (59.72) values of L* corresponds to dark and light roast conditions respectively, and consistent with the results of other authors [8,19,20,32].  
At constant feeding capacity i.e., 10 kg, it is observed from the 3D surface plot (Figure 4c) that the lowest conveyor speed and thermal oil flow rate decreased L* to 37.68 during roasting whereas  
Figure 4: (a) Interactive effect of conveyor speed and feeding capacity on L. (b) Interactive effect of thermal oil flow rate and feeding capacity on L*. (c) Interactive effect of thermal oil flow rate and conveyor speed on L*.  
on maximum levels, L* was found to be 60.59. However, L* is influenced more significantly by the thermal oil flow rate than conveyor speed. The color of groundnut kernels was darkened rapidly at lowest thermal oil flow rate because the availability of higher activation energy for molecules to start the browning reaction [36; 37; 38] also supported the fact that in high temperature-short time roasting, color is developed at faster rates due to availability of suitable activation energy in earlier stages. The variations in L* is due to thermal modification in microstructure of groundnut kernels, which occurs differently at different temperature [39]. Different time and temperature combination can be used to obtain the desired values of L* [20; 31; 34] also investigated the effect of time and temperature on roasted groundnut color and their results also support the obtained value of L*.