# Quality Assessment of Banana Ripening Stages by Combining Analytical Methods and Image Analysis
## 3 Results and Discussion
### Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectra Interpretation  
The bands of the ATR-FTIR spectra of the banana-flesh samples (Table 2, Figure S2) were obtained at a spectral range of 3300-500 cm\({}^{-1}\). All spectra presented absorption bands typically associated with starch, carbohydrates, water, organic acids, and phenolics. Specifically, the absorption band at 3640-3530 cm\({}^{-1}\) was appointed to the O-H stretching vibration, which is characteristic of phenolic compounds [40], while the wide band at 3300-3200 cm\({}^{-1}\) was due to the stretching vibrations of the hydroxyl groups, which are present in water, carbohydrates, organic acids, and phenols [41; 42]. Moreover, the two bands at 3400 and 3325 cm\({}^{-1}\) were ascribed to the asymmetric (higher frequency) and symmetric N-H stretching vibrations of the primary amines, respectively [40]. The 2932 cm\({}^{-1}\) band was assigned to the symmetrical stretching vibrations of the C(sp\({}^{3}\))-H of the carboxylic acids, the free amino acids, and the carbohydrates [41; 42], whereas the band at 1738 cm\({}^{-1}\) corresponded to the C-O stretching vibration of the carbohydrates and the phenolics [43]. The band at 1647-1632 cm\({}^{-1}\) was related to the bending vibrations of the water, the carbohydrates, the organic acids, and the phenolic hydroxyl groups. According to [PERSON] et al. [44], this was directly associated to the moisture content of the banana sample. The band at 1465-1450 cm\({}^{-1}\) was due to the scissoring vibrations of the monosaccharides, including the methylene and methyl groups [45]. Moreover, the band at 1420-1410 cm\({}^{-1}\) was linked to the combination of the C-H rocking and O-H bending vibrations [42; 46] or with the in-plane bending vibrations of C-H in amylose and amylopectin [45]. The band at 1366-1339 cm\({}^{-1}\) was related to the O-H bending vibration  
Figure 8: Pairwise correlation matrix between physicochemical parameters of the banana flesh and the features L\({}^{*}\), a\({}^{*}\), b\({}^{*}\) of the banana peel, during storage. of the C-OH group [42]; the band at 1261-1229 cm\({}^{-1}\), to the C-O stretching vibration of the carbohydrates and the phenolics [47]; and the band at 1153-1149 cm\({}^{-1}\), to the C-O and C-C stretching vibrations of the glycosidic linkage of the polysaccharides [48]. The band at 1105 cm\({}^{-1}\) was ascribed to the C-O and C-C stretching vibrations of the polysaccharides and the pectin [49], and the band at 1076 cm\({}^{-1}\) was related to the stretching of the C-OH bond of the starches [50]. The band at 1055-1045 cm\({}^{-1}\) was due to the C-O bending and C-OH stretching vibrations in the structure of the carbohydrates [51], which mainly corresponded to the sucrose and fructose absorption [52]. Moreover, the band at 1000-995 cm\({}^{-1}\) was related to the B-type crystalline structure of the starch, which was representative of the high amylose starches contained in fruits [53; 54; 55; 56]. The band at 928 cm\({}^{-1}\) was ascribed to the in-plane bending vibrations of C-OH and C-C in the glycosidic linkage of the amylose and the amylopectin [45; 57], and the band at 865-858 cm\({}^{-1}\) was representative of the ordered or crystalline structure of the starch [58]. The band at 770-735 cm\({}^{-1}\) was assigned to the C-H out-of-plane bending vibrations corresponding to the ortho-substituted aromatic rings [43], whereas the band at 720 cm\({}^{-1}\) was related to the O-H out-of-plane bending vibrations of the amylose and the amylopectin [40; 45]. Moreover, the 577 and 523 cm\({}^{-1}\) bands corresponded to the C-O-C in-plane bending vibrations of the glycosidic linkage of the amylose and the amylopectin [45]. The assessment of the ATR-FTIR spectra of the banana-flesh samples (Table 2) resulted in the findings summarized below.