## 3 Results and Discussion
### Volatile Compounds in CB Coffee Samples  
A total of 36 volatile compounds, including phenolic compounds such as guaiacol, pyrazines, pyridines, and pyrroles, were identified (Table 4). The relative standard deviation (RSD, %) for each coffee sample and threshold of each volatile compound are listed in Tables 5 and 6, respectively. Pyridine (V1) is known to have bitter, burnt, roasted, and astringent characteristics ([PERSON] et al., 2018; [PERSON] et al., 2018), and it can give a sharp burnt taste at concentrations as low as those on the ppm scale ([PERSON] et al., 2018). In this aspect, only StarbucksCS (1229 ng/mL) and TwosomeplaceCS (1695 ng/mL) might have a burnt taste. Pyridine is produced by trigonelline degradation and Maillard reactions ([PERSON] et al., 2018), especially in coffee that is subjected to high temperatures or strong roasting processes ([PERSON] et al., 2018). According to [PERSON] et al. (2018), the degree of roasting and preparation process contributed to aroma profiles rather than the coffee variety. Corresponding to this research, Blending CB and CM samples showed relatively higher contents of pyridine (694 and 643 ng/mL) than those in Colombia and Kenya samples of CB (521 and 508 ng/mL) and CM (268 and 309 ng/mL), respectively. As indicated by the sample sellers, the blending sample was roasted to the city level (about medium-dark roasting), and Colombia and Kenya beans were roasted to a medium level. Commercially ground coffee, Folgers, had a higher pyridine content, although it was indicated as a medium-roasted, and BaristaRTD had a higher pyridine content than those of other RTD samples. The CS samples had the highest amount of pyridine among all the evaluated coffee samples. In the case of 3-ethylpyridine (V6), which was correlated with a roasted, burnt aroma ([PERSON] et al., 2018) and tobacco flavor ([PERSON] et al., 2018), was found in TwosomeplaceCS and BaristaRTD at higher concentrations. N-acetyl-4-(H)-pyridine (V12) showed higher concentrations in CS and Folgers samples. The threshold of furfural (V3) was 3 ppm ([PERSON] et al., 2018), which was significantly higher than the furfural contents of all the coffee samples in this study. Main phenolic compounds such as guaiacol, 4-ethylguaiacol (V29), and 4-vinylguaiacol (V31) were also identified. The threshold of guaiacol and 4-vinylguaiacol (V31) was reported to be 3 ppb ([PERSON] et al., 2018; [PERSON] et al., 2018). Guaiacol is related to smoke, sweet, and medicinal characteristics ([PERSON] et al., 2018), and it evokes a burning sensation even if it exists at very low concentrations ([PERSON] et al., 2018). 4-ethylguaiacol (V29) and 4-vinylguaiacol (V31) are known to be associated with spice and clove flavors ([PERSON] et al., 2018). 4-ethylguaiacol (V29) is known to have a \"spicy-medicinal\" highly powerful odor ([PERSON] et al., 2018). Folgers samples showed higher contents of both 4-ethylguaiacol (V29) and 4-vinylguaiacol (V31), and the CS and Folgers samples had higher contents of guaiacol. Meanwhile, pyrazines are known to have roasted and earthy characteristics in ground coffee ([PERSON] et al., 2018). The contents of 2,6-dimethylpyrazine (V5) associated with nutty coffee odor ([PERSON] et al., 2018), methylpyrazine (V2), 2-ethyl-3-methylpyrazine (V9), and 5H-5-methyl-6,7-dihydroxycoplectu[b]pyrazine (V25) were higher in the CS and Folgers samples. Folgers and TwosomeplaceCS samples had higher amounts of 2-ethyl-3,5-dimethylpyrazine (V18), which has roasted cocoa odor ([PERSON] et al., 2018), 3-ethyl-2,5-dimethylpyrazine (V17), and 2,5-diethylpyrazine (V19) than those of the other samples. Diffurfuryl ether (V30) has a coffee-like and toasted odor ([PERSON] et al., 2018), and BaristaRTD, CS, and Folgers samples had higher amounts of diffurfuryl ether (V30) than the other samples. Folgers and CS samples contained higher amounts of 2-furanmethanol (V4) and 2-methyl-5-propionylfuran (V24).