## 3 Results and Discussion
### Interpretation of ATR-FTIR Spectra from Tomato Peels  
The ATR-FTIR spectra absorption bands detected on the outer surfaces of tomato peels during storage (as shown in Table 1 and Figure 5) were in the 4000-499 cm\({}^{-1}\) spectral range, and their study led to several important discoveries. The band observed at 3356 cm\({}^{-1}\), which is linked to the stretch of O-H found in water, organic acids, carbohydrates, and phenols [38; 52], showed a significant (\(p<0.05\)) increase from day 10 to day 14, and then stabilized until the end of the storage period. The band at 1602 cm\({}^{-1}\), associated with the bending vibrations of the hydroxyl groups, and correlated to the moisture content [53] of the tomato' peels, showed insignificant variations during the storage period. The bands observed at 2922 and 2854 cm\({}^{-1}\), presented the asymmetric and symmetric stretch of C(sp\({}^{3}\))-H in methylene present in triglycerides, carboxylic and fatty acids, carbohydrates, free amino acids, waxes, and especially the waxy polymer cutin [36; 52; 54], demonstrated a consistent (\(p<0.05\)) decrease from day 17 and day 14, respectively, which continued until the end of storage. In full agreement with the above findings, the absorbance at 1460 cm\({}^{-1}\), ascribed to the bending vibrations of methylene groups [55; 56] in cutin, lipids, carbohydrates, and proteins, showed a meaningful (\(p<0.05\)) decrease from day 14 to 17 of the storage period. In accordance with the above findings, it has been reported that  
Figure 4: Scatter diagram, principal component, and truth tables of the tomato peel samples discrimination, employing the textural features, among days 3, 14, and 24.  
during the gradual ripening of tomatoes in storage, the biopolymers such as cutin and polysaccharides such as pectin--which constitute the cell walls--are depolymerized or converted into more water-soluble structures, which results in the fruit softening [57; 58; 59]. The band at 1726 cm\({}^{-1}\), associated with the stretch of C=O in cutin, triglycerides, polysaccharides, and phenolic esters [35; 54; 55], exhibited a decrease (\(p<0.05\)) on both day 7 and day 17. In contrast, the band at 1708 cm\({}^{-1}\), related to the stretching of C=O in carboxylic  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Regions** & \multirow{2}{*}{**Day 3**} & \multirow{2}{*}{**Day 7**} & \multirow{2}{*}{**Day 10**} & \multirow{2}{*}{**Day 14**} & \multirow{2}{*}{**Day 17**} & \multirow{2}{*}{**Day 24**} \\ (cm\({}^{-1}\)) & & & & & & \\ \hline
3356 & 0.746 \(\pm\) 0.013a \({}^{*}\) & 0.761 \(\pm\) 0.032a & 0.766 \(\pm\) 0.026a & 0.859 \(\pm\) 0.015b & 0.876 \(\pm\) 0.013b & 0.885 \(\pm\) 0.014b \\
2922 & 0.729 \(\pm\) 0.016a & 0.708 \(\pm\) 0.019a & 0.712 \(\pm\) 0.007a & 0.720 \(\pm  
and fatty acids [55], first appeared on day 10 of storage and showed stable absorption until the end of storage. The absorbance at 1624 cm\({}^{-1}\), which is related to the stretch of _cis_-vinylene in carotenoids or in the (C-C) ring of pectin or the amide I band [54, 60], exhibited a progressive and substantial (\(p\) < 0.05) decrease until the 10 th day and then disappeared. Absorbances at 1558 and 1512 cm\({}^{-1}\), which are attributed to the C=C-C stretch in phenolic compounds' aromatic ring [55], revealed a noteworthy (\(p\) < 0.05) increase on the 7 th day of storage and then the absorbance of the first band remained constant, while that of the second band decreased significantly on the 17 th day of storage and returned to its initial value. Interestingly, the absorption intensities of the band at 833-831 cm\({}^{-1}\), assigned to the C-H bend of the para-substituted aromatic rings [55], showed exactly the same changes as the absorption at 1512 cm\({}^{-1}\). The band at 550-542 cm\({}^{-1}\) (ring torsion of the phenyl group) [56] presented insignificant variations during storage.