## 3 Results and Discussion
### Effective Wavelengths
RMSE variations (**A–C**) and average correlation (**D–F**) for red, yellow, and orange varieties, respectively. Figure 7: The vitamin C content of the three bell pepper varieties using SVM. These diagrams compare the performance of algorithms in terms of accuracy and error score. RMSE variations (**A–C**) and average correlation (**D–F**) for red, yellow, and orange varieties, respectively. Figure 8: The total phenol content of the three bell pepper varieties using SVM. These diagrams compare the performance of algorithms in terms of accuracy and error score. RMSE variations (**A–C**) and average correlation (**D–F**) for red, yellow, and orange varieties, respectively. Figure 9: The anthocyanin content of the three bell pepper varieties using SVM. These diagrams compare the performance of algorithms in terms of accuracy and error score. RMSE variations (**A–C**) and average correlation (**D–F**) for red, yellow, and orange varieties, respectively. Based on the literature data, spectral bands within specific ranges are associated with various biochemical components in bell peppers. Bands at 700-800 nm (third overtone of O-H from carboxylic and enediol acids) and 800-900 nm (second overtone O-H from carboxylic and enediol acids) are potentially linked to pH, titratable acidity (e.g., malic acid), and vitamin C content (as an enediol acid). Additionally, the region near 910-930 nm, attributed to C-H stretching from carboxylic acids [59; 64], is likely related to these parameters as well. Bands near 768 nm (fourth overtone of C-H) and 986 nm (second overtone of O-H) are associated with sample pH [65]. Given the absence of organic acids in the 600-700 nm range [64], it is probable that spectral features in this region primarily reflect the color of bell peppers. Furthermore, the 921-1039 nm range (9622-10,854 cm\({}^{-1}\)), particularly at 938, 938.5, and 998 nm, falls within the third-order overtone band of OH groups associated with cellulose [66] and, consequently, firmness [67]. Notably, specific wavelengths within this range (978.5 and 975 nm, 929 and 999.5 nm, and 930.5 and 924 nm) were identified as crucial for estimating total phenols and anthocyanins in red, yellow, and orange bell peppers, respectively, using SVM-PSO [68; 69]. These findings suggest a correlation between this spectral region and the content of phenols and anthocyanins, compounds containing one or more hydroxyl groups (O-H). Finally, wavelengths between 550 and 750 nm are likely influenced by variations in anthocyanin and chlorophyll concentrations [54]. Wavelengths within the 950-1075 nm range (encompassing the second and third overtones of O-H and C-H vibrations) and near 910 nm (third overtone band of O-H), specifically 911, 949, 956.5, 959.5, 975.5, 976, 988, 991.5, 999, and 1000 nm, have been identified as particularly important for detecting the soluble solid content (SSC) of bell peppers using SVM-PSO. These wavelengths may also be crucial for SSC calibration [59; 70]. Wavelengths around 700 and 950 nm (specifically 700, 700.5, 701, 949, 949.5, and 951.5 nm in their study) likely correspond to the third overtone stretch of C-H and the second and third overtones of O-H in water [71]. Additionally, a strong absorption peak near 975 nm (attributed to the second overtone of O-H) was associated with water and carbohydrates [72]. As each wavelength carries complex information about various compounds, isolating the composition of a specific substance solely based on these wavelengths proves challenging. Consequently, data analysis becomes indispensable for uncovering the hidden relationship between spectral data and qualitative properties.