## 4 Discussion
### Mineral Compositions and Total Polyphenol Contents  
The macroelement content decreased in the order K \(>\)Mg \(>\) P \(>\) Ca \(>\) Na, while the microelement content decreased in the order Fe \(>\) Mn \(>\) Cu \(>\) Zn. A similar trend in macro- and microelement contents was reported in green coffee beans from different regions of Ethiopia [48]. The highest macro- and microelement, N, C, H, and polyphenol contents, were found in Robusta medium-dark-roast beans (C2), while the lowest were found in Arabica medium-roast beans (C4), excepting Na and Zn. The differences between the highest and the lowest contents of each macro- and microelement were between 22 and 50%, around 50% for N and S, 30% for Polyphenols, and 3% for C, indicating that coffee production influences the composition of the final product. Based on their mineral contents and the almost complete transfer of minerals from coffee beans to final beverages, the studied coffee varieties are possible sources of minerals in the human diet [2; 8; 24; 48]. At the same roasting intensity, the Robusta variety has higher contents of Na, K, Ca, Mg, Fe, Cu, Mn, Zn, P, N, C, S, and polyphenols than the Arabica variety. In the case of Arabica, with increasing roasting intensity, K, Ca, Mg, Fe, Cu, P, N, S, and polyphenol contents increase, while contents of Na, Mn, Zn, C, and H are not influenced by roasting intensity. The differences in the elemental concentrations might be due to factors related to variety, soil type, fertilizers, and pesticides used in cultivation, as well as technological processes [7]. Similar contents of macro- and microelements in ground coffee beans were reported by [PERSON] et al. [8] for coffee brews made and served in a coffee shop in Poland. The high variability of major elemental contents allowed for geographical differentiation between roasted Arabica coffee samples produced in different regions of Mexico with good accuracy [23]. Polyphenols are linked to health-promoting properties, such as antioxidant, anti-inflammatory, antidiabetic, and anticarcinogenic activities [8]. The content of antioxidant compounds is also influenced by the roasting process [46]. Polyphenols are thermolabile molecular structures that decompose during drying and roasting due to the high temperatures and enzymatic browning processes. The highest content of polyphenols was measured in Robusta medium-dark-roast beans (C2, 18.9 g GA/kg), the lowest in Arabica medium-roast (C4, 13.3 g gallic acid/kg), which indicates that the content of polyphenols slightly increases with the roasting process and is higher in Robusta than in Arabica species. Similarly, [PERSON] et al. reported higher phenol contents in roasted Robusta beans than in roasted Arabica beans [49]. Oppositely, decrease in total polyphenols with increase in roasting intensity and higher total polyphenol contents in Arabica as compared with Robusta species were reported by [PERSON] and [PERSON] [46]. The opposite results of different studies may be attributed to the different origins of the studied coffee beans, their different climates and soils leading to different levels of polyphenol contents in the green beans [46; 50]. Generally, the Robusta variety (C2) had slightly higher elemental contents, although, except for Cu and polyphenols, the differences were not significant at a probability of 0.05 compared to the other coffee samples. The dark-roast Arabica coffee beans (C1, C6) had significantly higher K, Ca, N, and S contents than the medium-roast Arabica beans (C4, C5). However, the other elements varied without a clear link with roasting intensity, depending on other conditions, such as origin, soil characteristics, etc. Except for the polyphenol contents being slightly higher in the medium-dark-roast Robusta than in the medium-dark-roast mixture of Robusta and Arabica, the other elements did not differ significantly between the two samples. Based on the elemental compositions and polyphenol contents, AHC (Figure 5) grouped the coffee beans into three clusters.