# Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products
## 3 Results
### FT-MIR Spectral Characterization of Samples
\begin{table}
\begin{tabular}{c c c} \hline
**Main Peak (cm\({}^{-1}\))** & **Wave Number Range** & **Samples** & **Typical Band** \\ \hline
3288 & 3655–3000 & A; B; C; D; E; F; G; H; I; J; K; L; & O–H stretching vibrations \\  & & M; N & H-bonded hydroxyl of polysaccharide (especially \\  & & M; N & hemicellulose and cellulose) or polyphenols \\  & & N–H stretch amide \\ \hline
2924 & 2990–2800 & A; B; C; D; E; F; G; H; I; J; K; L; & C–H\({}_{1}\), C–H\({}_{2}\), and C–H\({}_{3}\) symmetric stretches of \\  & 2990–2800 & M; N & hydro carbonated skeleton of polysaccharide \\ \hline
2849 & & A; B; M; J; M; N & and carbohydrates \\ \hline
1743 & 1800–1701 & A; B; C; D; E; F; G H; I; J; K; L; & C=O stretching vibration of the carboxylic acid \\  & & M; N & methyl ester (i.e., pectins) \\ \hline
1620 & 1700–1500 & A; B; C; D; E; F; G; H; I; J; K; L; & C=O stretching vibration of free carboxyl groups (pectin and protein) \\  & & M; N & C=C stretch aromatic (phenols) \\ \hline
1404 & & & \\
1372 & 1499–1200 & A; B; C; D; E; H; F; G; I; J; K; L; & C–H\({}_{2}\) bending (xyloglucan, cellulose) \\  & 1372 & & M; N & C–C stretch aromatic (phenols) \\
1253 & & & C–H\({}_{3}\) groups C–O stretching (sugars) \\ \hline
1100 & & & A; B; C; D; E; F; G; H; I; J; K; L & C–O stretching (aromatic ring phenols), \\  & & & C–C stretching (cellulose) \\ \hline
1030 & 1199–1001 & A; B; C; D; E; F; G; H; I; J; K; L; & \\  & & M; N & \\ \hline
988 & & & A; B; C; D; E; G; H; I; J; K; L & \\ \hline
922 & & & \\
868 & & & A; B; C; D; E; G; H; I; J; K; L; & C–O bending (pectins), \\  & 829 & & M; N & C=C stretch (aromatic ring) \\ \hline
892 & & & C–H bending of benzene ring of phenols \\ \hline
776 & & & M; N & \\ \hline \end{tabular}
\end{table} 
Table 3: Spectral features of peel and pomace samples (A = apple peel; B = apple pomace; C = orange; carrot peel; D = orange carrot pomace; E = black carrot peel; F = cucumber peel; G = kumquat peel; and pomace; H = parnsnip peel; I = mango peel; J = mango pomace; K = peach peel; L = peach pomace; M = black plum peel; N = black plum pomace). Figure 2: _Cont._  
The spectral band centered at about 1620 cm\({}^{-1}\) was in all samples and it was assigned to the C=O stretching vibration of free carboxyl groups (lignin, benzene ring, pectin, and protein), the C=C stretch of the aromatic ring, and from the superimposition of the H-O-H bending of the amid I and C-N stretching of proteins [64]. The signals at 1620 cm\({}^{-1}\) were higher in vegetable samples than fruit samples, probably due to the different protein content. The spectral region between 1491 and 1200 cm\({}^{-1}\) of all samples was characterized by three main peaks, respectively, at 1404, 1372, and 1253 cm\({}^{-1}\). The first two peaks (1404 and 1372 cm\({}^{-1}\)) could be assigned to the C-O and CH\({}_{3}\) stretching of the carboxylic group related to organic acids and sugars, while the signal at 1253 cm\({}^{-1}\) could refer to the C-O in hydroxybenzene, the bending vibration absorption peak of C-O in the benzene ring, and to the C=C stretch aromatic characteristic of polyphenols, as reported by [PERSON] et al. [66] and [PERSON] et al. [67]. A high variability of signal intensity was observed among samples, highlighting the maximum intensity (value lower than 75%) for cucumber peel and the minimum in parasip peel (value lower than 85%), in accordance with the chemical determination of total phenols (Table 2). The spectral bands between 1199 and 1000 cm\({}^{-1}\) allowed us to identify specific band profiles, which are typical for the different hydroxyl-aromatic molecules that constitute the phenolic compounds (i.e., tannins) and alkanes that are the bons of polysaccharides (i.e., cellulose), as observed by [PERSON] et al. [68]. The peaks near 1100 cm\({}^{-1}\) and 1030 cm\({}^{-1}\) were assigned to C-O stretching (aromatic ring phenols) and C-C stretching (cellulose). The first peak was found in all samples except for cucumber and black plum peels, whereas the second peak was not found only in the black plum peel sample.