## 3 Results and Discussion
### Volatile Composition of Sea Fennel Leaf, Flower, and Fruit EOs and Hydrolates
To examine the differences in sea fennel leaf, flower, and fruit hydrolates, an HSP-SPME-GC-MS analysis was performed (Table 2). As expected, the hydrolates contained more polar compounds than those found in the EOs, since their constituents are generally water-soluble. Monoterpenes, the predominant constituents of the EOs, were typically absent in the hydrolates due to their higher affinity for lipophilic environments [37]. In total, 63 volatile compounds were identified in the sea fennel hydrolates. The greatest diversity was observed in the fruit hydrolate, with 48 compounds identified, followed by the leaf hydrolate, with 43, and the flower hydrolate, with 32 compounds. Monoterpenoids represented the most abundant class of compounds across all three plant parts, with the highest proportion observed in the fruits (87.4%) and the lowest in the leaves (75.25%). The second most prevalent group was monoterpene hydrocarbons, accounting for 12.55% in the leaves, while sesquiterpenoids were notably present in the flowers (10.7%). Ketones, esters, and phenol were detected only in the leaves (Table 2). Considering that the volatiles in the hydrosols predominantly originated from oxygenated constituents of the essential oils, the high content of monoterpenoids in the hydrosols was an expected outcome. Terpinen-4-ol was identified as the most abundant compound in the leaf and flower hydrolates (27.8% and 36.7%, respectively) and was also present in significant amounts in the fruit hydrolate (10.6%). Sabinene, one of the dominant compounds in the flower and fruit EOs, appeared in the hydrolates in its oxygenated forms, (\(Z\))- and (\(E\))-sabinene hydrate. (\(Z\))-Sabinene hydrate was detected at 5.9% in the flowers and 2.5% in the fruits, while (\(E\))-sabinene hydrate was found at 7.4% in the flowers and 3.0% in the fruits. Similarly, (\(Z\))- and (\(E\))-carveol, the hydroxylated derivatives of limonene, were detected in high concentrations across all samples. (\(Z\))-Carveol was most abundant in the fruit hydrolate (11.4%), while (\(E\))-carveol was the highest in the leaf hydrolate (7.3%). The fruit hydrolate was also rich in (\(E\))-isocarveol (10.6%) and (\(E\))-\(p\)-mentha-2,8-dien-1-ol (9.0%). The flower hydrolate contained a considerable amount of spathulenol (8.3%), while the leaf hydrolate was characterized by 10-(acetylmethyl)-3-care (8.6%), which was absent in the flower and fruit hydrolates. Previous studies on sea fennel leaf hydrolates collected in Central Dalmatia in August and October similarly identified terpinen-4-ol as the most abundant volatile compound (13.86% and 41.93%, respectively), followed by 10-(acetylmethyl)-3-caree (13.45% and 13.80%, respectively). Comparable levels of sabinene hydrates (1.54-4.73%) and (_E_)-carveol (3.36%-4.92%) were also reported [21; 22]. \(\alpha\)-Terpineol was present in similar concentrations in all the samples, and increased slightly from the leaves to the flowers to the fruits (4.2% < 5.8% < 6.9%). A one-way ANOVA revealed no significant differences in the \(\alpha\)-terpineol levels between the samples. However, significant differences were found for terpinen-4-ol, (_Z_)-carveol, and carvone in all the hydrolates. The flower hydrolate exhibited significantly different levels of (_Z_)- and (_E_)-sabinene hydrate and spathulenol compared to the other hydrolates, while the fruit hydrolate differed significantly in its content of (_E_)-_p_-mentha-2.8-dien-1-ol. Terpinen-4-ol, the most abundant volatile compound in all the sea fennel hydrolates, exhibits a wide range of pharmacological properties, including strong antimicrobial and antivirulent activity as well as antioxidant, anti-inflammatory, antihypertensive, and anticancer effects. Isolated mainly from tea tree oil, terpinen-4-ol can be synthesized by the hydration of sabinene or obtained via the oxidation, hydrogenation, and selective hydrogenation of terpinolene [38]. Terpineol occurs in four isomeric monoterepenoid forms, including terpine-4-ol and \(\alpha\)-terpineol.