2.2.3. Thermal Analysis

Thermogravimetry (TGA) and differential scanning calorimetry (DSC) were carried out simultaneously. The analyses were performed at air atmosphere at a temperature range from 30 to 600 ◦C, with a heating rate of 10 ◦C per minute.

Figure 5 shows DSC curves for pectin polysaccharide (powder), curcumin (powder), and pectin aerogel loaded with curcumin. Chitosan-coated pectin aerogels loaded with curcumin were not subjected to TGA/DSC analysis due to the size and weight limits.

**Figure 5.** Differential scanning calorimetry (DSC) curves for curcumin powder, pectin powder and pectin aerogel loaded with curcumin.

The DSC curve for curcumin shows a clear peak at 178 ◦C, indicating the melting point of the substance. The curve for pectin shows an exothermic peak at 237 ◦C, indicating a degradation of this polysaccharide. As for pectin, the DSC curve for pectin aerogel loaded with curcumin has an exothermic degradation peak at 225 ◦C. In this case, the peak is shifted to the left, which means that the degradation occurs earlier. On the other hand, the melting peak of the curcumin is not visible on the pectin–curcumin curve.

Simultaneously with DSC, TGA was measured as presented in Figure 6.

**Figure 6.** Thermogravimetry (TGA) curves for curcumin powder, pectin powder, and pectin aerogel loaded with curcumin.

The values read from TGA curves are given in Table 2. The thermal degradation of pectin polysaccharide as well pectin aerogel loaded with curcumin occurs in the two steps. The main decomposition (62%) occurs at higher temperatures, which is confirmed by DSC curves (exothermic degradation peaks at 237 and 225 ◦C). Decomposition of curcumin of 59% occurs in one step and corresponds to the melting of the substance.

**Table 2.** Mass degradation of curcumin powder, pectin powder, and pectin aerogel loaded with curcumin.


### 2.2.4. Fourier Transform Infrared Spectroscopy

Figure 7 presents infrared (IR) spectra for curcumin powder, pectin aerogels loaded with curcumin, and chitosan-coated pectin aerogels also loaded with curcumin.

**Figure 7.** Infrared (IR) spectra: curcumin powder (black), pectin aerogel loaded with curcumin (red), and chitosan-coated pectin aerogel loaded with curcumin (green).

IR spectrum of curcumin clearly shows characteristic peaks [19]: 3500 cm<sup>−</sup><sup>1</sup> for phenolic O-H stretching, 1628 cm<sup>−</sup><sup>1</sup> aromatic moiety C=C stretching, and 1600 cm<sup>−</sup><sup>1</sup> benzene ring stretching vibrations identifying curcumin. Furthermore, the IR spectrum contains C=O and C=C vibrations at 1508 cm<sup>−</sup>1, olefinic C-H bending vibrations at 1427 cm<sup>−</sup>1, and aromatic C-O stretching vibrations at 1278 cm<sup>−</sup>1.

The IR spectrum for pectin aerogels loaded with curcumin shows a characteristic peak at 1743 cm −1, presenting esterified carboxyl groups. Peaks at 1625 cm<sup>−</sup><sup>1</sup> and 1600 cm<sup>−</sup><sup>1</sup> are clearly visible, confirming the presence of loaded curcumin.

Lastly, the IR spectrum of chitosan-coated pectin aerogels show characteristic peaks at 1604 cm<sup>−</sup><sup>1</sup> presenting N-H bending of the primary amine, 1398 cm<sup>−</sup><sup>1</sup> and 1327 cm<sup>−</sup><sup>1</sup> presenting CH2 bending and CH3 symmetrical deformations. These peaks are the characteristic signature of chitosan. Characteristic peaks for curcumin, however, are overlapping with peaks of chitosan; hence, they are not visible in the spectrum. The presence of curcumin was later confirmed by in-vitro release studies.
