## 3 Results and Discussion
### Volatile Compounds in Fermented and Unfermented Coffee Beans  
As shown in Table 4, a total of 18 compounds (3 phenols, 5 pyrazines, 4 acids and esters, 3 furan and furanic compounds, 2 ketones, and 1 anethole) were identified and semi-quantified in the coffee samples, and some showed significant differences between the fermented and unfermented coffee samples. Both acetic acid and propanoic acid were organic acids that were detected relatively higher in fermented coffee beans, which is correlated to the study conducted by [PERSON] et al. [60]. The presence of organic acids in coffee beans has confirmed the microbial action that is involved in the fermentation process, mainly due to the degradation of the nuclage layer by lactic acid bacteria (LAB) and acetic acid bacteria (AAB) [59; 61]. As shown in Table 4, acetic acid was found to be the predominant organic acid in fermented coffee beans, which has an average amount of 9.058 ug/mL. However, there was a negative influence of acid presence on the quality or acceptance of the coffee beverages according to [PERSON] et al. [62]. Propanoic acid was detected in all fermented coffee samples, with an average amount of 0.298 ug/mL. The bacteria of the genus _Bacillus_, specifically _B. megaterium_, could be responsible for this acid production during coffee bean fermentation [63]. Although all five pyrazines identified in this study could be found in both fermented and unfermented coffee samples, the content of all five pyrazines detected in the fermented coffee samples was relatively higher than in the unfermented coffee samples. The compound 1, pyrazine, was the highest at 1.286 ug/mL compared to the other four pyrazines. Pyrazine compounds were generally related to nutty, roasty, and earthy aromas [64]. It arises as the same Maillard reaction occurred in both fermented and unfermented coffee samples due to the same roasting degree achieved. The formation of Amadori-type conjugates differs in the Amadori rearrangement between the dipeptide and sugar adduct, resulting this pyrazine clusters [65]. All five pyrazines were identified before in a previous study conducted by [PERSON] et al. [9] and showed the same outcome, as fermented coffee beans presented a higher level of pyrazines than unfermented coffee beans. There were three furan and furanic compounds detected in the coffee samples. The content of 2-furanmethanol and furfural was relatively higher than the 5-methyl-2-Furancarboxaldehyde. As furrans are commonly developed from the reaction between sugars and amino acids, during fermentation, the amount of sugar in the coffee bean will be reduced and result in less furan production than the unfermented coffee bean [66]. Thus, microbial activities could contribute to the formation of these furan and furanic compounds via their impacts on the volatile precursor during fermentation [67; 68]. 2,3-Butanediol has the relatively highest content of the three phenolic compounds identified in the fermented coffee samples, while the concentrations of the other two compounds were not significantly different between the fermented and unfermented coffee samples. 2,3-Butanediol can be produced during yeast fermentation, involving the reduction in diacetyl formed from the valine biosynthetic pathway, and contributes to a fruity, creamy, buttery flavor. It is commonly detected in commercially purchased coffee beans due to uncontrolled spontaneous fermentation [69; 70]. A controlled and suitable fermentation process could be used and included in coffee bean processing for the desired quality of coffee bean products. However, further sensory analysis needs to be implied to test the relative sensory attributes generated in the coffee fermentation process. \begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline \multirow{2}{*}{**No.