## 4 Discussion
### Volatile Organic Compounds  
The compositions of volatile organic compounds in green and roasted beans differed considerably. The most important aromatic compounds are formed during roasting. Green beans do not contain coffee aromatic compounds, though they have similar groups of compounds. Furans were the most abundant group of volatiles present in the coffee samples, their contents being higher than 40%, although their amounts varied between samples, as follows: C3 (57.1%) > C5 (50.8%) > C1 = C6 (49.4%) > C2 (48.3%) > C4 (44.5%). The same volatile organic compounds were reported in studies on roasted coffee beans [21; 33; 34; 35] and brewed coffee [36]. Furans are cyclic ethers mainly found in condensates from carbohydrates that undergo browning reactions. As green coffee beans contain large amounts of sugars, mainly sucrose, these compounds are formed through thermal processes, such as coffee roasting, when degradation and rearrangement of carbohydrates, ascorbic acid, and unsaturated fatty acids occur [19; 37; 38]. The thermal degradation of d-glucose and sugar polymers into furanic compounds as major decomposition products was also reported by [PERSON] et al. [39]. Serine, threonine, and sucrose decompose into heterocycles as simple furans, furanones, and furan rings. Our data (Table 1) align with reports in the literature that roasted Arabica coffee beans have higher contents of stream-volatile furrans than the Robust variety because of the high sucrose contents [40; 41]. Although the presence of furans in thermally treated foods, such as roasted coffee, is mainly attributed to carbohydrates resulted in Maillard-reaction, it could also result from the thermal oxidation of lipids, thiamine degradation, and higher nucleotide or terpene breakdown [42]. The 2-methylfuran was the most prevalent furan compound detected in the samples (13.7-22.8%), except for the C1 sample, in which 2-furanmethanol was the dominant (11.6%) volatile compound. This compound was previously identified in both green and roasted coffee [39; 43]. Furfural (19.6-4.7%) and furans (13.7-5.8%) were also found in high amounts in all samples, being responsible for the chocolate, caramelly, nutty, creamy, bready, and ethereal doors of coffee. The second prevalent group of compounds identified in coffee samples was ketones, which also constitute an essential class of volatile compounds. They represent about 20-27% of coffee aromatic components, having as representatives 2,3-pentanedione and 2-butanone. As in the case of furans, unroasted coffee beans do not contain these compounds. They are formed through roasting when the Maillard reaction leads to diketone formation following the heating of the glucose in the coffee beans. They also were identified as the representative aliphatic volatiles formed after the thermal interaction of glucose and cysteine [43]. According to studies in the literature, ketone amounts increase with roasting temperature and duration [44]. Similar to the other compounds, even ketone amounts differed among the studied samples. Pyrazines are also characteristic aromatic compounds specific to roasted coffee. Methylpyrazine was identified in all the studied coffee samples, the highest amounts being detected in C1, C2, and C4 (>4% of the total detected volatile organic compounds). Pyrazines provide various odors, such as nutty, roasted, corn, hazelnut, potato or earthy aromas, depending on the substituents of the pyrazine ring; pyridine is related to bitter, fishy or burnt odors, while pyrrole provides nutty notes [19]. Pyrroles are primarily formed thermally; they are not present in fresh or raw foods, excepting 1-methylpyrrole and 2-acetylpyrrole, which have been identified in green coffee [41]. Pyrroles are formed by the reaction of aldoses with alkylamines, in a reaction involving reducing sugars and amino acids by condensation of glucose and alanine, or of glucose and proline or hydroxyproline [41]. These compounds have nutty, hay-like, and herb aromas [45].