## 3 Results and Discussion
### Volatile Composition of Single-Dose Espresso Coffee-Based Blends
This suggests that these compounds, if present in amounts higher than their odor threshold values, can contribute to the overall aroma of the coffee samples under study. To make a global and fast visual comparison among the volatile composition of coffee powders and espresso brews of the eight capsule-coffee blends, radar graphs with the total GC \(\times\) GC peak area data for each chemical family were constructed (Figure 2a,b) based on data from Table S2. The relative proportion of GC \(\times\) GC peak area for each family and the relative contribution of the number of compounds in each family is also presented (Figure 2c). Globally, furan compounds and pyrazines were the major chemical families determined considering the GC \(\times\) GC peak area on both coffee matrices, corresponding respectively to 35.5-45.9% and 11.5-19.4% in coffee powders and 45.2-53.3% and 11.7-16.5% in espresso brews of the total GC \(\times\) GC peak area. The predominance of furans and pyrazines over other chemical families was already described for different coffee samples as the main coffee brew aroma contributor [15], related to sweet, fruity, spicy, coffee, nutty, toasted, and roasted notes (Table S1). Moreover, among the 36 pyrazines herein determined, alkylpyrazines such as 2-ethylpyrazine and 2-ethyl-6-methylpyrazine have been previously indicated as potent key odorants in coffee [13; 67]. Radar representations in Figure 2a,b show that the volatile compounds profile was different considering GC \(\times\) GC peak areas among the samples within each matrix, with the  
Figure 2: Capsule-coffee blends’ volatile profile analysis. Total GC \(\times\) GC peak area grouped by chemical family of (**a**) coffee powders and (**b**) espresso coffee brews, and (**c**) contribution of each family to the total area (right column refers to the number of compounds in each chemical family). differences in the coffee espresso brews being more prominent compared to those of the powders. Indeed, a similar volatile composition was determined among the eight capsule-coffee powders under study, with the chemical families linked to the industrial roasting process having less variation; namely, pyrazines (1.3-fold), furan compounds (1.6-fold), and acids (1.5-fold). Showing a contrasting composition were volatile phenols (2.3-fold), sulfur compounds (3.7-fold), and varietal ones such as terpenic compounds (3.9-fold). Blend Dec (decaffeinated) exhibited a lower content of terpenic compounds, although with the highest areas considering volatile phenols. Regarding volatile phenols, for origin blends the lowest GC \(\times\) GC peak areas were determined in Blend 6 (from Ethiopia--3.8 \(\times\) 10\({}^{8}\)) and higher values in Blend 5 (5.8 \(\times\) 10\({}^{8}\)--Tanzania) and Blend 4 (7.2 \(\times\) 10\({}^{8}\)--Jamaica). This trend was also observed for these brews (Figure 2, Table S2). Volatile phenols, such as guaicaol, 4-ethylguaicaol, and 4-vinylguaicaol are well-known for their smoky, spicy, and phenolic notes (Table S1), which suggest distinct aroma properties of these origin capsule-coffees. Sulfur compounds, such as 2-furfurylthiol and 2-furylmethylsulfide, contribute with garlic and coffee notes. Thus, the powder of Blend 4 should stand out among all samples due to the lowest GC \(\times\) GC peak areas of these compounds. The opposite was observed for Blend 5. Moreover, the lower relative content of varietal compounds determined in Blend Dec (terpenic and norisoprenoids compounds), well-known for their fruity, sweet, and floral notes (Table S1), could be related to the decaffeination process, similar to what has been observed for other chemical families in decaffeinated coffees [25; 68]. While the variation among powder samples ranged from 1.3 to 3.9-fold (RSD (%)--relative standard deviation expressed as a percentage--of 9-38% among all samples) in the respective brews the variation increased to 2.3-6.8-fold (RSD of 29-63%). Indeed, only the chemical family of sulfur compounds varied less in brews (3.3-fold) than in coffee powders (3.7-fold).