## 3 Results and Discussion
### Interpretation of ATR-FTIR Spectra from Tomato Peels
The absorbance at 1344 cm\({}^{-1}\), related to the C-H bending vibration of polysaccharides and cellulose ring [56] exhibited an increase (\(p\) < 0.05) on the 7 th day of storage and subsequently remained stable till the end of the storage duration. The band at 1280 cm\({}^{-1}\), attributed to the amide III band due to the combined C-N stretch and N-H and O=C-N bend in peptides and proteins [56], or to O-H in-plane bending in primary or secondary hydroxyl compounds (cutin and hydroxy fatty acids) [55], showed a gradual and marked (\(p\) < 0.05) increase on the 7 th and 10 th day. The band at 1220 cm\({}^{-1}\), which is ascribed to the C-O stretch of carbohydrates, phenolics, and steroidal alkaloids and their glycosylated forms [31, 38], presented a significant (\(p\) < 0.05) increase on the 7 th and 10 th day of storage. The absorptions at 1165 and 1105 cm\({}^{-1}\), due to the C-O and C-C stretches of the glycosidic linkage in polysaccharides and pectin and C-O stretching vibrations of monosaccharides [61, 62], showed no significant variations except for the decrease in intensity at 1165 cm\({}^{-1}\) from day 17 of storage. The bands at 1056-1050 and 1028-1022 cm\({}^{-1}\) are connected to the C-O bending and stretching vibration of the carbohydrate's C-OH groups, including pectin substances, glucose, and fructose [43, 56]. The increase (\(p\) < 0.05) in intensity at 1056-1050 cm\({}^{-1}\) on day 7 could be linked to pectin hydrolysis into simple sugars. In view of the above results, it is reported [9] that tomato storage at 10 and 24 \({}^{\circ}\)C leads to carbohydrate conversion, biosynthesis, and hydrolysis to simple sugars. Furthermore, the decrease (\(p\) < 0.05) in intensities at 1165, 1056-1050, and 1028-1022 cm\({}^{-1}\) at day 17 or 24 could be attributed to the consumption of total sugars by respiration during storage [29]. The absorptions at 970 and 721 cm\({}^{-1}\), linked to _trans_- and _cis_-C-H out-of-plane bending vibrations of the carotenoids, respectively [55], showed a gradual and significant (\(p\) < 0.05) increase until day 17, and then remained constant or decreased until the end of storage, respectively. The carotenoid content of tomatoes, especially lycopene and beta-carotene, increased with increasing storage time and was significantly influenced by storage conditions (temperature and light presence) and the ripening stage of tomato fruits [9, 24]. In addition, [PERSON] et al. (2010) reported that lycopene content in tomato peel significantly decreased in overripe tomatoes [23]. Finally, the bands at 630-623 and 518-514 cm\({}^{-1}\) related to the O-H out-of-plane and to the glycosidic linkage (C-O-C) in-plane bending of pectin, respectively [38], displayed insignificant changes during storage. Additionally, the tomatoes were grouped according to the different storage days using the intensities of the spectral bands at 721, 1165, and 1624 cm\({}^{-1}\), achieving a discrimination accuracy of 100.0%. The scatter diagram (Figure 6) shows, the correct classification of all samples on days 3 (blue circles), 7 (green squares), 10 (red triangles), 14 (pine green pentagons), 17 (purple triangles), and 24 (yellow pentagons). All samples were correctly classified by the machine learning CART classifier.