# Thermal and Kinetic Properties of Brazilian Coffee Arabica Beans
## 3 Results and Discussion
### Thermogravimetric Analysis  
The thermogravimetric (TG) curves were evaluated and the first derivative (DTG) for all the coffee samples was calculated. In Figure 1, the TG and DTG curves of green, light and dark roasted coffee beans in an oxygen and nitrogen atmosphere with a heating rate of 10 \({}^{\circ}\)C per min are shown. A heating rate of 10 \({}^{\circ}\)C per min was used, according to the methodology of [PERSON] et al. (2011).  
The thermal decomposition of coffee samples in oxygen occurs in four stages. The first stage ranged from 50 to 200 \({}^{\circ}\)C, second--from 200 to 350 \({}^{\circ}\)C, third--from 350 to 425 \({}^{\circ}\)C and fourth--from 425 to 700 \({}^{\circ}\)C.  
On the DTG curve, two peaks were observed. In the case of the first peak maximum in DTG curves was observed at the temperature of 200 \({}^{\circ}\)C and the second at about 425 \({}^{\circ}\)C. The first region was characterized by the soft loss of material weight about 4-6% for roasted coffee samples and about 7-9% for green coffee beans. The low weight loss rate in the initial stage can be attributed to the evaporation of moisture trapped inside the coffee matrix. In the next region, coffee samples undergo a fast decomposition. A significant weight loss is caused by the alteration of some components such as saccharides decomposing as well as by a rapid release of volatiles from the sample material ([PERSON] et al., 2016; [PERSON] et al., 2016). The last, fourth zone revealed a very slow weight loss rate.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Coffee Sample** & **T\({}_{\text{g onset}}\) (\({}^{\circ}\)C)** & **T\({}_{\text{g midpoint}}\) (\({}^{\circ}\)C)** & **T\({}_{\text{g endpoint}}\) (\({}^{\circ}\)C)** & **Water Activity a\({}_{\text{w}}\)** \\ \hline Green & \(-\)19.99 \(\pm\) 1.17 \({}^{\text{a}}\) & \(-\)11.24 \(\pm\) 0.84 \({}^{\text{a}}\) & \(-\)1.69 \(\pm\) 0.24 \({}^{\text{a}}\) & 0.486 \(\pm\) 0.007 \({}^{\text{c}}\) \\ Light & \(-\)19.89 \(\pm\) 0.21 \({}^{\text{a}}\) & \(-\)11.93 \(\pm\) 0.16 \({}^{\text{a}}\) & \(-\)2.49 \(\pm\) 0.05 \({}^{\text{b}}\) & 0.399 \(\pm\) 0.002 \({}^{\text{b}}\) \\ Dark & \(-\)19.81 \(\pm\) 0.28 \({}^{\text{a}}\) & \(-\)11.87 \(\pm\) 0.13 \({}^{\text{a}}\) & \(-\)2.48 \(\pm\) 0.01 \({}^{\text{b}}\) & 0.388 \(\pm\) 0.003 \({}^{\text{a}}\) \\ \hline \hline \end{tabular} Different letters indicate that the samples are considered significantly different (\(\alpha\) = 0.05) in terms of roasting degree.  
\end{table}
Table 1: Onset, midpoint and endpoint of the glass transition temperature determined in coffee samples (\(\pm\)) standard deviation (SD) from triplicate measurements.  
The profiles of the TG and DTG curves of samples analysed in nitrogen atmosphere were determined. In this case, we can only distinguish the following three phases: one from 50 to 150 \({}^{\circ}\)C, next from 150 to 335 \({}^{\circ}\)C and last from 335 to 700 \({}^{\circ}\)C. In the nitrogen atmosphere, the weight loss rate was slower than in the oxygen. The first mild peak  
Figure 1: Thermogravimetry/derivative thermogravimetry (TG/DTG) curves of Brazilian green (BZ), light roasted (BZ) and dark roasted (BC) coffee samples in oxygen (O\({}_{2}\)) and nitrogen (N\({}_{2}\)) atmospheres.  
maximum was observed at 75-85 \({}^{\circ}\)C and the weight loss can be associated with the evaporation of moisture [30]. The second DTG peak maximum was observed at 300 \({}^{\circ}\)C and the third at 375 \({}^{\circ}\)C. The second peak shows the decomposition of saccharides and the third the decomposition of fatty acids [25; 30].  
[PERSON] et al. [31] and [PERSON] et al. [32], who both investigated the thermal properties of coffee residues, observed similar trends.