# Characterization of Thermal Properties of Ruby Chocolate Using DSC, PDSC and TGA Methods
## 3 Results
### Oxidative Stability Measuring by PDSC
The value of activation energy E\({}_{\text{a}}\) and pre-exponential factor Z for the oxidation of pure cocoa butter analyzed by [PERSON] et al. [40] were 106.2 kJ/mol and 5.6 \(\times\) 10\({}^{10}\), respectively, regarding T\({}_{\text{on}}\) values. Based on the Arrhenius theory, the oxidation process in the case of oil with a high E\({}_{\text{a}}\) value is faster at high temperatures, whereas for oil with a low E\({}_{\text{a}}\) value the process is faster at low temperatures. Activation energy should not be considered as the only parameter used to assess the oxidative stability of lipid products. [36]. In the anhydrous milk fat dynamic oxidation process, the starting temperature of oxidation is shifted to lower values with the increasing ratio of unsaturated/saturated fatty acids [37]. More importantly, the calculated kinetics parameters (E\({}_{\text{a}}\), Z and k) are also decreased. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Induction Time (\(\tau_{\text{on}}\))** & **Induction Time (\(\tau_{\text{max}}\))** \\ \hline a & 5284 \(\pm\) 626 & 4359 \(\pm\) 244 \\ b & \(-\)12.46 \(\pm\) 1.61 & \(-\)9.31 \(\pm\) 0.61 \\ R\({}^{2}\) & 0.990 & 0.990 \\ E\({}_{\text{a}}\) (k/mol) & 96.21 \(\pm\) 11.39 a  & 79.37 \(\pm\) 4.44 b  \\ log Z & 12.46 & 9.31 \\ Z (1/min) & 2.88 \(\times\) 10\({}^{12.4}\) & 2.05 \(\times\) 10\({}^{9}\) b  \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Regression analysis of the DSC data for the fat extracted from ruby chocolate—activation energies (E\({}_{\text{a}}\)) and pre-exponential factors (Z) based on onset and maximum induction time (\(\tau_{\text{on}}\) and \(\tau_{\text{max}}\)). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Oxidation Onset Temperatures** & **Oxidation Maximum Temperatures** \\  & **T\({}_{\text{on}}\)** & **T\({}_{\text{max}}\)** \\ \hline a & \(-\)4534 \(\pm\) 85 & \(-\)4419 \(\pm\) 33 \\ b & 10.75 \(\pm\) 0.18 & 8.83 \(\pm\) 0.07 \\ R\({}^{2}\) & 0.995 & 0.965 \\ E\({}_{\text{a}}\) (k/mol) & 82.54 \(\pm\) 1.54 a  & 80.45 \(\pm\) 0.61 a  \\ log Z & 9.07 & 7.16 \\ Z (1/min) & 1.17 \(\times\) 10\({}^{9}\) a  & 1.44 \(\times\) 10\({}^{7}\) b  \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Regression analysis of the DSC data for the fat extracted from ruby chocolate—activation energies (E\({}_{\text{a}}\)) and pre-exponential factors (Z) at onset and maximum temperatures (T\({}_{\text{on}}\) and T\({}_{\text{max}}\)). Both CB and MF represent fats with a significant majority of saturated fatty acids (SFA). However, MF is a source of short fatty acids such as caproic, caprylic, lauric or myristic acid, which are more prone to oxidation than palmitic or stearic acid, typical cocoa butter ingredients. Even though cocoa butter is also a good source of oleic acid, it is predominantly composed of symmetrical triacylglycerglycerols with oleic acid in the 2-position (POP, POS, SOS). This position of the oleic acid should not diminish the good oxidative resistance of cocoa butter [29]. Overall, it can be concluded that the presence of a small amount of MF in ruby chocolate has a noticeable influence on decreasing the oxidative resistance of the fat extracted from RC when compared with pure cocoa butter. In the second experimental procedure, the oxidative stability of the fat extracted from the ruby chocolate was assessed by measuring onset and maximum oxidation induction time (OIT) in isothermal mode (Table 4). The values of \(\mathrm{E_{a}}\) and \(\mathrm{Z}\) of the oxidation process, calculated using regression (Equations (1)-(5) of the onset and maximum induction time for each temperature, are presented in Table 3. The higher the oxidation temperature, the shorter time needed to reach full fat sample oxidation. There is no published data for the induction time of pure cocoa butter at T = 120 \({}^{\circ}\)C. However, considering the high values of \(\mathrm{E_{a}}\) and \(\mathrm{Z}\), it can be expected that pure cocoa butter has a very large OIT.