Thermal Decomposition Behavior of Hydroxytyrosol (HT) in Nitrogen Atmosphere Based on TG-FTIR Methods

Abstract

The thermal decomposition behavior of olive hydroxytyrosol (HT) was first studied using thermogravimetry (TG). Cracked chemical bond and evolved gas analysis during the thermal decomposition process of HT were also investigated using thermogravimetry coupled with infrared spectroscopy (TG-FTIR). Thermogravimetry-Differential thermogravimetry (TG-DTG) curves revealed that the thermal decomposition of HT began at 262.8 °C and ended at 409.7 °C with a main mass loss. It was demonstrated that a high heating rate (over 20 K·min−1) restrained the thermal decomposition of HT, resulting in an obvious thermal hysteresis. Furthermore, a thermal decomposition kinetics investigation of HT indicated that the non-isothermal decomposition mechanism was one-dimensional diffusion (D1), integral form g(x) = x2, and differential form f(x) = 1/(2x). The four combined approaches were employed to calculate the activation energy (E = 128.50 kJ·mol−1) and Arrhenius preexponential factor (ln A = 24.39 min−1). In addition, a tentative mechanism of HT thermal decomposition was further developed. The results provide a theoretical reference for the potential thermal stability of HT.

Thermal Stability of Amorphous Solid Dispersions

“…Transition from the AS state (unstable) towards the CS state (stable) stands in correlation with thermodynamics, kinetics, and drug-excipient interactions. Knowledge of thermal behavior, especially the kinetics, leads to lifetime prediction [ 7 , 8 ], which is essential for prediction of the storage conditions of drugs, as well as for technological processing.…”

“…What can we learn from thermal stability data? First, the onset temperature of degradation that goes in favor of the thermal behavior of drug can be determined [ 3 ]; Second, we can get insight into the mechanism of thermal decomposition of drugs and potential degradants (i.e., the relationship between the molecular structure and thermal stability) [ 7 ]; Third, understanding of compatibility/incompatibility between drug and excipients is revealed [ 8 ]; Fourth, we learn about its solubility potential [ 9 ]; Finally, information on handling/storage of drugs, shelf-life, and usage can be provided [ 10 ].…”

Hydroxytyrosol and Oleuropein-Enriched Extracts Obtained from Olive Oil Wastes and By-Products as Active Antioxidant Ingredients for Poly (Vinyl Alcohol)-Based Films

“…In particular, a visible increase of the degradation rate was observed in the case of HTyrE, with the first DTG (derivative weight loss) peak occurring at 203 °C and the main peak, centered at 305 °C, due to the decomposition of more stable compounds [ 12 , 37 , 38 ]. Mass loss was 73% in the interval between temperatures 200 and 500 °C, which suggested the cracking of –C–C–, –C=C–, and –OH bonds to further form CO 2 , H 2 O, and carbonaceous material [ 39 ]. In the case of OleE, the maximum degradation peak was shifted to 235 °C, with a shoulder at 352 °C; the increased thermal stability compared to HTyrE can be related to the more complex chemical structure of OleE, which is able to justify the delayed thermal degradation [ 40 , 41 ].…”

Olive Pomace Phenolic Compounds Stability and Safety Evaluation: From Raw Material to Future Ophthalmic Applications

“…The low thermal stability of OL and HT has already been demonstrated [ 67 , 68 ]. However, it is important to highlight that the stability of these compounds in aqueous solutions is lower than in solid state [ 69 ] or in olive oil [ 30 , 66 ].…”