## 3 Results and Discussion
### Volatile Compounds Identified in Currant Samples Using HS-SPME-GC-FID/MS Method
These are important components of cheese aroma (with a typical mushroom note) but also occur naturally in some plants and have, surprisingly, been identified as key components of black currant aroma [6,12,13]. Carboxylic acids are important components of plant foods. Acids up to C\({}_{10}\) play a significant role in aroma, not only directly but also as precursors to other aromatic substances (esters, lactones, etc.). Only acetic acid was identified in the samples; it is formed by sugar degradation (glucose, fructose, and sucrose) and, along with malic and citric acids, is a major contributor to fruit sourness [31]. Sulfur compounds should also be mentioned. Although present at very low concentrations, they are known to contribute to the characteristic flavor of black currants [15,19]. They were not detected in the samples, likely because their concentrations were below the detection limit of the method used. Their thermal lability might be another reason for their absence. In contrast to black currants, there are very few studies on red/white currants. [PERSON] et al. [18] investigated the chemical composition of various berry fruits (e.g., sea buckthorn, blueberry), including red currants. They identified 18 volatile compounds, of which only the esters methyl, ethyl, and octyl acetate were consistent with our findings. The only more comprehensive study is that of [PERSON] [26], who studied volatile constituents of fresh red and white currants in greater detail. Using liquid-liquid extraction, they identified a total of 139 compounds in red currants and 92 in white currants. The major classes were C\({}_{6}\) compounds (i.e., C\({}_{6}\) alcohols and aldehydes) and acids, with (Z)-3-hexen-1-ol, (Z)-3-hexenal, (E)-2-hexenal, 1-octen-3-one, acetic acid, linalool, and \(\beta\)-damascenone identified as key components of red currant aroma. With the exception of (Z)-3-hexenal, all of these were also identified in our samples of red/white currants, although not in all varieties (see Table S1). In total, 40, 39, and 54 volatile compounds were identified in red, white, and black currants, respectively (see Table S1). As expected, and consistent with [PERSON] [26], the red and white currants were quite similar in terms of identified compounds, as they belong to the same species, _R. rubrum_, while black currants had the most substances, mainly from the group of terpenoids. Of all identified terpen, sabinene, \(\delta\)-3-carene, and rose oxide have not yet been identified in red/white currants and could, therefore, be tentatively considered specific to black currants. Alcohols, aldehydes, and esters were the most numerous in all currant variants (red/white/black). In contrast to black currants, terpen and terpenoids constituted only a minor compound class in the red variants, which is also consistent with [PERSON] [26]. Regarding the individual cultivars within the red/white/black variants, they were similar in terms of identified compounds (see below). Typical HS-SPME-GC-FID chromatograms of compounds identified in selected representatives (the sensorially most acceptable) of red/white/black cultivars are depicted in Figure 1, showing clear differences in the volatile composition between black and red/white currants. Figure 1: Example of HS-SPME-GC-FID chromatograms of compounds identified in selected red/white/black currant cultivars (**(a)** white Victoria, **(b)** red Rubigo, and **(c)** black Demon). For peak identification, see Table S1 in Supplementary Material).