*3.1. Raw Materials Characterization*

Different biomolecules, such as ChNFs and polyphenols, from natural sources were applied onto the tissues to obtain functional tissues with enhanced properties. Before the application on the substrate, active molecules were characterized to identify their main composition. In Table 2, the main results obtained from the TGA thermogram are reported.

**Table 2.** Main components of cellulosic tissues elucidated by TGA.


TGA analysis confirmed that the tissue was mainly composed of cellulose (81.63%), with a water content of 5.66%. The residue obtained under nitrogen atmosphere accounted for 12.71 wt%, which was mostly attributed to carbonaceous derivatives or organic additives that can be oxidized under air (final residue in air was 1.1 wt%).

Powders of active molecules were analysed by ATR-FTIR to qualitatively determine their composition.

The polyphenols spectrum showed typical bands associated with amide (1650 and 1540 cm−1) and lipid (1720–1650 cm−<sup>1</sup> and 3000–2800 cm−1) groups. Other bands occurring at 1440–1400 cm−<sup>1</sup> (C-H bending) and 1240–1400 cm−<sup>1</sup> (C-C and C-C-H stretching) indicated the presence of methyl groups of proteins, and 1170–1115 cm−<sup>1</sup> was attributed to C-O stretching. Broad absorption bands of OH group were shown in the 3500–3000 cm−<sup>1</sup> range. The two peaks at 2920 and 2850 cm−<sup>1</sup> were related, respectively, to asymmetric and symmetric C-H stretching. The region between 1040 and 990 cm−<sup>1</sup> showed intense bands attributed to C-O-C vibrational modes of various carbohydrates and acids, which are abundant groups in tomatoes [75]. Finally, a small peak related to C=O stretching (1720 cm<sup>−</sup>1) showed the presence of acetate groups.

In Figure 3, the FTIR spectrum of the polyphenol powder was compared with the one obtained from the sprayed polyphenols solution on an aluminium foil. This comparison evidenced a correspondence between main bands except for the band appearing at 990 cm−1, which was attributed to the C-O-C vibrational modes of carbohydrates and organic acids derived from tomato [76]. This difference can be ascribed to the different surface composition detected by ATR-FTIR in the case of the powder or spray suspension. In the latter case, electrolytic substances are reasonably more concentrated on the surface than in the case of the powder.

**Figure 3.** Spectra of polyphenols powder (top) and its sprayed film deposited on an aluminium foil.

Typical peaks related to acetyl and amide groups of chitin were observed in the spectrum of Figure 4. C-H stretching was identified at 1850 cm<sup>−</sup>1, and the bands observed at 1548 cm−1, 1615 cm−1, and 1650 cm−<sup>1</sup> were typical of amide groups. N-H stretching band relatives to deacetylated groups of chitin were observed at 3270 cm<sup>−</sup>1. Other typical peaks related to the chitin carbohydrate backbone were the C-H stretching band shown at 2870–2880 cm−1, the O-H wide band at 3450 cm−1, and C-O-C stretching at 1025 and 1075 cm−<sup>1</sup> [77]. The comparison between ATR-FTIR results for ChNF powder and its spray on aluminium in Figure 4 evidenced a good correspondence between both spectra.

**Figure 4.** Spectra of chitin powder (top) and its sprayed film deposited on an aluminium foil.

The ChNF structure was studied by FESEM. The micrograph reported in Figure 5 showed a nanometric structure of chitin composed of fibrils with a diameter <50 nm.

**Figure 5.** ESEM micrograph obtained for ChNFs.

Regarding the composition of polyphenols determined by HPLC-DAD-MS, chlorogenic acid, rutin, and naringenin were mainly identified in the tomato seeds powder. The quantification of these polyphenols was performed, in triplicate, based on integrated peak areas of samples and standards using external calibration. As a result, 2.99 ± 0.11 mg/100 g, 1.38 ± 0.02 mg/100 g, and 1.11 ± 0.35 mg/100 g were obtained for naringenin, rutin, and chlorogenic acid, respectively. These results are in agreement with other authors who reported similar polyphenols contents in tomato seeds [78].
