## 3 Results
### Results and Evaluation of FTIR Spectra  
Structural analysis of the more bioactive amphiphilic compounds was carried out via ATR-FTIR, by which specific characteristic peaks for phenolics, carotenoids and polar lipids were detected, as compared to similar peaks of characteristic functional groups of standards used like \(\beta\) caroten, soy polar lipids, a non-flavonoid phenolic acid (the hydrolysisable tannin, gallic acid) and some different types of flavonoids (the flavonol quercetin and the flavan-3-ol catechin) (Table 7). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Compound** & **Wavenumber Range (cm –1)** & **Absorption Description** \\ \hline \multirow{2}{*}{\(\beta\)-Carotene} & 3050–2850 & C-H and C-C bonds of alkyl and conjugated double bonds \\  & 1600–1500 & C-C absorption related to conjugated bonds in carotenoids \\  & -950 and -720 & Characteristic absorptions for conjugated double bonds \\ \hline \multirow{3}{*}{Polar Lipids} & 3500–3200 & O-H absorption from hydroxyl groups \\  & 2950–2850 & C-H absorption due to fatty chains \\  & 1750–1735 & C-O absorption from ester groups \\  & 1450–1375 & CH\({}_{2}\) and CH\({}_{3}\) groups \\ \hline \multirow{3}{*}{Gallic Acid} & 3500–3200 & O-H (hydroxyl) bonds, specific for this functional group in phenolic compounds \\  & 1700–1600 & C-O from carboxylic groups (\textless{COOH}) \\  & 1600–1400 & Aromatic C-C stretching \\  & 1200–1000 & C-O vibrations from phenolic groups \\ \hline \multirow{3}{*}{Quercetin} & 3500–3200 & O-H (hydroxyl) bonds, specific for this functional group in phenolic compounds \\  & 1700–1600 & C-O from ketone groups in phenolic rings \\  & 1600–1400 & Aromatic C-C bonds \\  & 1200–1000 & C-OH and C-O-C vibrations in phenolic/ether groups \\ \hline \multirow{3}{*}{Catechin} & 3500–3200 & O-H (hydroxyl) bonds, specific for this functional group in phenolic compounds \\  & 1700–1600 & C-O from ketone/aldehyde groups in phenolic rings \\  & 1600–1500 & Aromatic C-C bonds \\  & 1200–1000 & C-O vibrations from phenolic groups \\ \hline \multirow{3}{*}{Sample} & \multicolumn{2}{c}{Wavenumber Range (cm–1)} & Absorption Description \\ \hline \multirow{3}{*}{TAC Apple Juice} & 3500–3200 & O-H (hydroxyl) bonds, specific for this functional group in phenolic compounds \\  & 2950–2850 & C-H stretching (alphatic chains, such as those present in fatty acids of PL) \\  & 1750–1700 & C-O stretching (carbonyl groups in esters for PL, as well as C=O from ketone/aldehyde groups \\  & 1200–1000 & C-O stretching (esters) and C-O vibrations from phenolic groups \\ \hline \multirow{3}{*}{TAC Apple By-Products} & 3500–3200 & O-H (hydroxyl) bonds, specific for this functional group in phenolic compounds \\  & 2950–2850 & C-H stretching (alphatic chains, such as those present in fatty acids of PL) \\  & 1750–1700 & C-O stretching (carbonyl groups in esters for PL, as well as C=O from ketone/aldehyde groups \\  & 1450–1375 & CH\({}_{2}\) and CH\({}_{3}\) bending vibrations as well as Aromatic C=C bonds \\  & 1200–1000 & C-O stretching (esters) and C-O vibrations from phenolic groups \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Main absorptions and descriptions of the peaks for absorption of characteristic functional groups present in TAC of apple juice and pomace compared to standard compounds analyzed. Particularly, in both TAC extracts, a broad absorption band appears around 3400 cm\({}^{-1}\), characteristic of -OH (hydroxyl) groups. This region is linked to the presence of alcoholic groups, such as those in bioactive phenolic compounds found in apples, as well as carboxyl groups in certain phenolic acids. These compounds, known for their strong antioxidant properties, are commonly found in plant-derived by-products like apple pomace. Peaks near 3000 cm\({}^{-1}\) correspond to the vibrations of C-H bonds in methyl (-CH\({}_{3}\)) and methylene (-CH\({}_{2}\)-) groups, which are typically present in the saturated acyl and alkyl chains of fatty acids in polar lipids (PL).