## 3 Results and Discussion  
Figure 3 shows significant differences (\(p<0.05\)) between samples in all sensors from the e-nose. It can be observed that the sensors with the highest voltage for all samples were MQ3 and MQ4 sensors, being Coffee I10 with the highest voltage. A study conducted using civet and non-civet coffee beans and measured using an e-nose that included some of the sensors in the present paper reported MQ7 sensor (Carbon monoxide (CO)) as the highest voltage followed by MQ3 (ethanol) and MQ4 [34]. The authors of the mentioned paper did not specify the conditions in which the measurements were performed; however, the fact that there is CO production during the roasting process of coffee beans [55] may explain their high levels in the MQ7 sensor. Therefore, the lower voltage associated with MQ7 in the samples presented in this paper may be associated with the brewing process. Table 3 shows the 45 identified volatile aromatic compounds using the GC/MS and the associated aromas. Peak area and retention times, as well as ANOVA-LSD results for each compound and sample, may be found in the Supplementary Material (Table S1). There were non-significant differences (\(p>0.05\)) between samples for compounds C2, C5, C7, C8, 12, C27, and C31; all other compounds presented significant differences (\(p<0.05\)) between the coffee samples. In Table 3, it can be observed that most of the volatile compounds are associated with coffee, cocoa, and nutty aromas, which have also been reported in other published studies, some of these are furanus such as 2,5-dimethylfuran (C2), 2-methoxylfuran (C8), 2-acetyllfuran (C12), 2,2-methylenebisfuran (C31), furfuryl propionate (C32); pyrazines such as 2-methylpyrazine (C7), 2-ethylpyrazine (C13), coffee pyrazine (C20), and nutty pyrazine (C36), among others [12; 13; 56]. The most abundant  
Figure 3: Stacked mean values of the electronic nose sensors showing the letters of significance that depict significant differences between samples according to the ANOVA and least significant differences (LSD) post hoc test (\(p<0.05\); \(\alpha=0.05\)). Differences are compared for each sensor among samples (bar colors). Samples and sensors description can be found in Tables 1 and 2, respectively. Error bars represent the standard error. compound based on the peak area for all samples was furfuryl acetate (C18), which has been related to fruit, banana, and ethereal aromas (Table S1); other authors have also found this compound in arabica [57], and robusta [58] coffees and they have associated this compound also with a floral aroma. Some compounds related to smoke have also been found, some of these are pyridine (C4) and phenols such as ortho-guaiacol (C33), 4-ethyl guaiacol (C43), and 4-vinyl guaiacol (C45), these are formed during the roasting process of the coffee beans [58; 59]. In this study, coffees with higher intensity presented larger peak areas for compounds C4, C33, C43, and C45, than lower intensities (Table S1). 3-Methylfuran (C1), which is considered a toxic, carcinogenic compound, was identified. This has been reported in studies from other authors and found to be formed during the roasting process of coffee [60; 61]; however, the International Agency for Research on Cancer (IARC) has not found sufficient evidence of possible carcinogenic effects due to coffee consumption [62]. Figure 4 shows that principal components one and two (PC1 and PC2) represented 77.55% of the total data variability. According to the factor loadings (FL; Table S2), the PC1 was mainly represented by the phenols C17, and C43, and the furan C44, all with FL = 0.20 on the positive side of the axis, and by furans C3 and C14, and aldehyde C9, all with FL = \(-\)0.18, on the negative side. On the other hand, on the positive side of PC2, it was mainly characterized by pyrazines C7 (FL = 0.30) and C13 (FL = 0.27), while on the negative side, it was described by furans C23 (FL = \(-\)0.29) and C32 (FL = \(-\)0.30).