## 2 Results and Discussion
### Targeted Analysis of Aroma-Related Volatile Compounds
#### 2.1.2 Chemical Families of Aroma-Related Volatiles  
As shown in Figure 1, some chemical families such as alcohols, pyrazines, lactones, pyrroles, phenols, pyridines, and sulfur-containing compounds showed higher peak areas in the regular coffee than in the decaffeinated coffee. The reduced formation of pyrazines is previously observed in DCM decaffeinated coffee [1]. The relatively lower content of alkylpyrazines in decaffeinated ground coffee was also reported [7]. Pyrazines are the principle pyrolysis products of sucrose during the roasting process [14]. Furthermore, a significant amount of sucrose is removed unintentionally together with caffeine during the decaffeination process [22; 23]. In fact, 60% and 20% losses in sucrose content were observed in the green beans of _Coffea arabica_ L. (Arabica) and Coffee canephora Pierre (Robusta), respectively, after decaffeination by DCM [22; 23]. Therefore, this explains why pyrazines were less concentrated in the decaffeinated coffees than in the regular coffees. During the roasting process, the pyrolysis of sucrose can also produce pyrroles [22]. Therefore, the number of pyrroles was relatively lower in the decaffeinated group. Besides the sucrose, chlorogenic acids are also partially removed during decaffeination (16% loss for Arabica and 11% loss for Robust) [23]. Chlorogenic acids are the precursors of phenolic derivatives and lactones [21; 22]. The content of phenolic compounds in the roasted ground coffee is related to the content of chlorogenic acids in the green beans [8]. Thus, this explains the lower content of phenols and lactones in the decaffeinated group. The decaffeination process extracts little amounts of proteins, lipids, and trigonelline as well. The roasting process degrades trigonelline into pyridines and pyrroles. During the Maillard reaction, the degradation of trigonelline, protein, and sucrose produces pyridines, pyrroles, and pyrazines [21]. Lipids are the precursors of alcohols. The decrease in lipids in decaffeinated green beans results, therefore, in the lower content of alcohols in roasted decaffeinated beans. In contrast, furans, acids, ketones and aldehydes showed higher peak areas in the decaffeinated coffees than the regular coffees (Figure 1). The coffee bean color turns to light brownish after the decaffeination process [1]. In a roasted coffee production site, the completion of the roasting process is partially decided by the color of the beans. Therefore, to achieve the same final color, the decaffeinated beans may need shorter time than the regular green beans, which means the decaffeinated beans may be less roasted. Generally, less roasted coffee presents more acidity [19]. This may explain the higher acid content in the decaffeinated coffees. The amount of some compounds such as diketones decrease with excessive roasting because they are formed in the early stages of roasting [19]. Therefore,  
Figure 1: The comparison of targeted aroma-related volatiles between regular and decaffeinated coffee ((**a**). R-R vs. D-R, (**b**). R-F vs. D-F, (**c**). R-VO vs. D-VO) according to the chemical family relative peak areas. In the abbreviations of the coffee samples names, the initial letters R and D indicate the coffee type: regular and decaffeinated. The second letters R, F, and VO indicate the label of the coffee capsule. The asterisk signs (*) displayed above certain chemical families indicate a significant statistical difference (\(p<0.05\), \(t\)-test) between the regular and the decaffeinated coffee. less roasting time of decaffeinated coffee cause higher ketone content. Aldehydes that impact flavor quality are produced from two pathways. The Strecker aldehydes, such as 2-methylbutanal and 3-methylbutanal, are the products of the Strecker degradation [24]. The precursors involved in Strecker degradation are amino acids and diketones derived from the Maillard reaction. The other pathway is from lipid oxidation of unsaturated fatty acids [19].