## 3 Results and Discussion
### Optimal Waveband Selection Using ANOVA Analysis Results
#### 3.2.1 Development of Single-Waveband Algorithm (SWA)
The calibration accuracies were 92.72% and 89.81%, and the validation accuracies were 92.85% and 89.75%, respectively. 492-nm and 660-nm were related to carotenoids and chlorophyll-\(b\), respectively [36; 37]. Residue Detection Algorithm for Apple  
For the SWA developed for detecting apple residue on the surface of 2B-finished SSS, the optimal waveband for the original juice, and the 1:5 and 1:10 dilution samples was 488 nm, and the threshold values for detecting the residues using the selected wavebands were 481, 415, and 382, respectively (Figure S1c). The calibration accuracies were 93.38%, 86.16% and 85.16% and the validation accuracies were 93.37%, 85.29% and 83.86%, respectively. The optimal wavebands for the 1:20, 1:50, and 1:100 dilution samples were close to 648 nm, and the threshold values for detecting the residues using the selected wavebands were 1707, 1556, and 1825, respectively. The 488-nm and 648-nm wavebands were related to carotenoids and chlorophyll-\(b\), respectively [36; 37]. For the SWA developed for detecting apple residue on the surface of #4-finished SSS, the optimal waveband for the original juice was 584 nm, the threshold value was 677, the calibration accuracy was 85.81%, and the validation accuracy was 85.17% (Figure S2c). The optimal wavebands for the 1:5 and 1:10 dilution samples were close to 470 nm, and the threshold values were 422 and 344, respectively. The calibration accuracies were 82.48% and 83.55%, and the validation accuracies were 79.47% and 72.34%, respectively. The optimal wavebands for the 1:20, 1:50, and 1:100 dilution samples were close to 660 nm, and the threshold values were 338, 437, and 487, respectively. The calibration accuracies were 80.63%, 71.83%, and 70.02%, and the validation accuracies were 77.48%, 70.04%, and 69.06%, respectively. The 470-nm and 660-nm wavebands were related to carotenoids and chlorophyll-\(b\), respectively [36; 37]. Residue Detection Algorithm for Watermelon  
For the SWA developed to detect watermelon residue on the surface of 2B-finished SSS, the optimal wavebands for the original juice, and the 1:5, 1:10, and 1:20 dilution samples were close to 470 nm, and the threshold values for detecting the residues using the selected wavebands were 861, 487, 382, and 260, respectively (Figure S1d). The calibration accuracies were 85.35%, 82.74%, 82.94%, and 82.55%, and the validation accuracies were 85.73%, 82.71%, 82.78%, and 78.10%, respectively. The optimal wavebands for the 1:50 and 1:100 dilution samples were 644 nm, and the threshold values were 1555 and 1642, respectively. The calibration accuracies were 75.48% and 67.53%, and the validation accuracies were 70.55% and 60.02%, respectively. The 470-nm and 644-nm wavebands were related to carotenoids and chlorophyll-\(b\), respectively [35; 36; 37]. For the SWA developed for detecting watermelon residue on the surface of 2B-finished SSS, the optimal wavebands for the original juice, and the 1:5, 1:10, and 1:20 dilution samples were close to 460 nm, and the threshold values for detecting the residues using the selected wavebands were 791, 434, 340, and 290, respectively (Figure S2d). The calibration accuracies were 89.04%, 87.71%, 88.54%, and 83.36%, and the validation accuracies were 89.22%, 86.91%, 86.03%, and 77.82%, respectively. The optimal wavebands for the 1:50 and 1:100 dilution samples were close to 660 nm, and the threshold values were 409 and 486, respectively. The calibration accuracies were 77.91% and 71.74%, and the validation accuracies were 69.30% and 70.76%, respectively. The 460-nm and 660-nm wavebands were related to carotenoids and chlorophyll-\(b\), respectively [35; 36; 37]. Tables 1 and 2 summarize the results of the ANOVA analysis performed to determine the optimal wavelengths to detect different samples. First, when the SWA was applied, the optimal wavebands for each of the dilution samples were similarly selected on the surfaces of 2B-finished SSS and #4-finished SSS.