## 3 Results and Discussion
### Total Phenolic Content  
Phenolics are chemical compounds with aromatic benzene rings containing hydroxyl groups generated by plants to protect against stress [26]. They provide antioxidant activity due to their hydroxyl groups acting as electron donors [27]. Moreover, some of those phenolic compounds have been reported to trigger the synthesis of endogenous antioxidant molecules in the cell [28]. In this study, the total phenolic contents of coffee extracts with various roasting degrees are shown in Table 3. Results showed that the total phenolic contents of espresso coffee were significantly higher at the Medium roasting than the Light-medium roasting (\(p<0.05\)). However, the total phenolic content in the espresso was significantly lower when prepared with the Moderately dark and Very dark roasted coffee beans compared to the Medium roasted coffee beans (\(p<0.05\)). In the drip, the phenolic content was the highest at the Light-medium, whereas the phenolic content at the Very dark roasting was significantly lower compared to the Medium and Moderately dark roasting (\(p<0.05\)). These results agreed with [PERSON] and [PERSON]'s results that the total phenolic compounds were 94.98-199.13 mg GAE/g and were the highest in water reflux extract of coffee beans (Columbia Valencia Supremo) roasted for 10 min and decreased with the longer roasting times [29]. It has been also reported by [PERSON] et al. that phenolic compounds in freeze-dried coffee extracted by hot water immersion of coffee beans (C. _arabica_ cv. Medellin) were 26.80-55.00 mg GAE/g and were the highest at the light roasting, decreasing along with an increase in roasting degree [30]. In a study by [PERSON] et al., green coffee beans originating from Java were roasted for different roasting times, and coffee brews were prepared through immersion of the coffee beans in boiling water [31]. Total phenolic contents in coffee brews prepared from coffee beans with medium roasting (18 min) and dark roasting (22 min) were 90.22 and 37.60 mg/100 mL, respectively, and were lower compared to the green coffee beans (180.69 mg/100 mL) [31]. The decrease in phenolic compounds might be because phenolic acid is unstable with intense heat and is easily decomposed [31]. However, it has been reported that some phenolic acids, including caffe, p-hydroxybenzoic, protocatechuic, vanillic, and ferulic, are increased in coffee beans with increasing roasting degree [32]. In this study, the content of TDS in espresso increased as the roasting degree increased, whereas the TDS content in the drip did not. Therefore, the slight increase of total phenolic contents in espresso coffee prepared using \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variable** & **Extraction** & **Light-Medium** & **Medium** & **Moderately Dark** & **Very Dark** \\ \hline Total dissolved & Espresso & 4.51 \(\pm\) 0.17 b  & 4.53 \(\pm\) 0.10 b  & 4.62 \(\pm\) 0.05 b  & 4.93 \(\pm\) 0.00 a  \\ solids (\%) & Drip & 1.19 \(\pm\) 0.00 a  & 1.02 \(\pm\) 0.00 b  & 1.05 \(\pm\) 0.05 b  & 1.13 \(\pm\) 0.05 a  \\ \hline \hline \end{tabular}  
* Data are expressed as mean \(\pm\) standard deviation (\(n=3\)). Means with different letters (a,b) in the same row denote significant differences according to the one-way analysis of variance (ANOVA) and [PERSON]’s multiple comparison test (\(p<0.05\)).  
\end{table} 
Table 2: Total soluble solids in coffee extracts.