# Aroma Profile of Monovarietal _Pet-Nat_ Ciders: The Role of Croatian Traditional Apple Varieties
## 3 Results and Discussion
### Volatile Compounds in Sparkling Pet-Nat Ciders
Their concentrations can vary depending on yeast strain, apple cultivar used, and fermentation conditions employed [51]. According to recent studies, HAs were the most abundant VCs in ciders and sparkling ciders [5; 15; 18; 45; 50; 52]. Generally, they are directly synthesized by yeast fermentation of sugars and the yeast metabolism of amino acids [53]. [PERSON] and [PERSON], in 1987 [54], found the total HAs in wine in the range 80-540 mg\(\cdot\)L\({}^{-1}\) with concentrations up to 300 mg/L, contribute to the pleasant aroma, but concentrations above 400 mg\(\cdot\)L\({}^{-1}\) produced unpleasant flavor and harsh taste. According to [PERSON] et al. [28] there are no differences in dominant alcohols (2-methyl-1-butanol, 1-propanol, isobutanol, and isoamyl alcohol) between ciders fermented by _Saccharomyces_ sp. or wild yeast, but treatment based on lees contact significantly increases HA levels [28]. In this study the highest concentration with a significant difference was noticed in 'Bo\(\beta\)cincia' _Pet-Nat_ cider. The most abundant compound in all three varieties was isoamyl alcohol with the content ranging from 11,360 to 12,825 mg\(\cdot\)L\({}^{-1}\), which is in accordance with published results [50; 52; 55]. The following HAs were 1-hexanol, 1-dodecanol, 1-propanol, 1-decanol, 1-butanol and phenylethyl alcohol. The same HAs including (6Z)-nonen-1-ol are listed in Table 5 as compounds with OAV \(>\) 1 that actively contribute to the aroma characteristics of wines [39]. The highest values were reported for melon/green and ripe fruit/alcoholic odors. _Fatty acids (FAs)_ are fermentation aromas produced by yeast and bacteria, their profile being related to apple cultivars and harvest [56]. In low concentrations they can have an impact on the complexity of the sensory characteristics, with fruity, cheese, fatty, and rancid aromas [57], while they have a negative effect when above their thresholds [58]. Among 13 detected compounds, hexanoic, octanoic, and isovaleric acid exceeded their thresholds, with the highest significant concentrations in 'Bo\(\beta\)cincia' _Pet-Nat_ cider (Table 5), with a goat cheese nuance. As mentioned, fatty acids, together with decanoic acid, were the main acids in ciders that agrees with previous researches [45; 52; 59]. [PERSON] et al. [28] reported an increase in hexanoic and octanoic acids in ciders undergoing the fermentation lees contact. It is significant to note that, despite conducting spontaneous fermentation and lees contact, the concentrations of total FAs were lower than 20 mg\(\cdot\)L\({}^{-1}\) in all variants, as it has been reported that higher concentrations have a negative impact on the final wine aroma [60]. _Terpenes_ mainly derive directly from fruits and contribute to the primary or varietal aroma of the wine. Because of their relatively low thresholds, they contribute to the floral and fruity aromas, either directly or through synergistic effects [61]. There was a significant difference in total terpen between the ciders, with the highest level in 'Bobovac' sparkling cider, mainly due to the compounds not detected in other varieties (_allo_-ocimene, _a_-ocimene, _cis-\(\beta\)_-f_arnesene and linalyl butyrate). Among the 13 terpen analyzed, only citronellol exceeded its odor threshold in 'Bo\(\beta\)cincia' and 'Bobovac', (Table 5), contributing to the cider aroma with a rose odor [58]. _a_-Terpinene and linalyl isobutyrate were compounds found only in 'Bo\(\beta\)cincia' cider, while significant differences between ciders were noticed only in menthol and geranyl formate concentrations. In comparison to research on apple wines with different treatments [5], the concentration of citronellol was more than 10-folds higher, and linalool was within the published ranges [5; 50]. [PERSON] et al. [50] detected only linalool oxide, linalool and _a_-f_arnesene in 'I'lzer rose' cider, with small but significant differences in concentrations regarding different fermentation strategies.