## 3 Results and Discussion
### Peeling off Cleaning
Thus, red and green variance peaks proved more appropriate to study the cleaning process since in this case, changes of variance were mainly due to changes from the white chemically attacked peanut butter to the white-gray of the bare steel surface. The peak observed  
Figure 7: Color intensity (**A**) and variance (**B**) changes during the chemical attack process of MF174 UW (1%) peanut butter product on S316 stainless steel. Peanut butter sample before (image 1) and after 24 h (images 2 and 3). Red, Green and Blue color lines correspond to RGB channels. for green and red color around 75 min corresponds to the time when one half of the surface remained covered by peanut butter and the other half was uncovered. Careful observation of the shape of the red color variance shows that it was quite asymmetrical, as corresponded to first or second kinetic orders (see Figure 3). Due to overlapping of two processes (chemical attack and peeling off), the resulting shape of these curves did not allow an accurate estimation of the half width at half maximum to discern between first and second kinetic orders (Table 2), but we can discard a zero-order kinetics reaction. An accelerated video of this process can be seen in the Supplementary Materials (Video S3). At higher concentration of the cleaning agent (3% of MF174 UW), we expected an acceleration of the cleaning process. Initially, the first color change to white was not  
Figure 8: 3D plots of mean color intensity (**A**) and variance (**B**) of red color during chemical attack of MF174 UW (1%) on peanut butter on S316 steel plate. Figure 9: The time evolution of mean color intensity (**A**) and variance of color intensity (**B**) during the process of cleaning of peanut butter from a steel plate with mechanical vibration (1% MF174 UW, 20 \({}^{\circ}\)C, vibration 11,000 rpm). Red, Green and Blue color lines correspond to RGB channels. observed. If we assume that the chemical attack was faster, then it is possible that the breakage and loss of adhesion to the metal may have taken place before the color change. Three-dimensional plots of blue color intensity and their variance against the elapsed time and the distance from the top of the electrode are presented in Figure 10. For the blue color intensity, we see that the final color was reached before 30 min (Figure 10A). The maximum of variance was reached at about 15 min without many differences from the distance from the top of the electrode (Figure 10B). The observed color changes were smoothed by the mechanical effect of the vibration together with the higher concentration of the detergent. Table 4 summarizes the results of the cleaning process at two temperatures, for two concentrations of the cleaning product and applying, or not, vibration as a mechanical action that helped the cleaning of the product. Table 4 allows us to corroborate that increasing the concentration of the cleaning product from 1% to 3% multiplied the cleaning speed by approximately two. It can be assumed that under the experimental conditions of this work, with the use of the vibrating electrode, it was possible to renew the solution in the vicinity of the peanut butter layer continuously. Therefore, the MF174 UW concentration remained constant. If we consider a simplified model in which the cleaning rate depends on both, the surface concentration of dirt (\(\Gamma_{d}\)) and on the solution concentration of MF174 UW ([MF174 UW]), we can write a rate equation as:  
\[rate=k\Gamma_{\text{d}}^{\text{e}}[MF174 UW]^{\beta}=k_{ap}\Gamma_{\text{d}}^{ \text{e}} \tag{5}\]  
\[k_{ap}=k[MF174 UW]^{\beta} \tag{6}\]  
Therefore, if the concentration is multiplied by 3 and the speed (estimated from \(t_{end}\) in Table 4) by (1.6-2.5), this means an experimental apparent kinetic order \(\beta\) for MF174 UW of 0.4-0.8.