## 3 Results and Discussion  
### High-Resolution Mass Spectrometry Analysis  
According to the literature [46], LO holds a large variety of bioactive molecules, in particular fatty acids and phenolic compounds, which are among the main ones responsible for its various beneficial properties, primarily the antimicrobial and antioxidant activities. Results will be presented and discussed below. Overall, the high-resolution mass spectrometric analysis (HRMS) of LO revealed almost 600 univocal molecular formulas, considering both ionization modes. VKd groups the metabolites according to their own O/C versus H/C molar ratio. In the vKd shown in Figure 1A is characterized by a large abundance of lipids, terpenoids and polykeptides, followed by a relevant number of amino acids and polyphenols. Furthermore, the vKd has been also used to highlight the metabolic pathways that occur among the entries, triggered by several chemical reactions. In Figure 1B, each group of reactions marks a line: along lines A (green lines) several hits have been found that are related by (de)hydrogenation reactions, e.g., for O/C = 0.28, heptenoic acid (C\({}_{7}\)H\({}_{12}\)O\({}_{2}\))/heptanoic acid (C\({}_{7}\)H\({}_{14}\)O\({}_{2}\)); for O/C = 0.31, gibberell acid (C\({}_{19}\)H\({}_{22}\)O\({}_{6}\))/gibberellin A1 (C\({}_{19}\)H\({}_{24}\)O\({}_{6}\)). Oxidation or reduction reactions are represented by lines B (red lines), along which succinidic acid (C\({}_{4}\)H\({}_{6}\)O\({}_{4}\))/sucinaldehyde (C\({}_{4}\)H\({}_{6}\)O\({}_{2}\)) for H/C = 1.50; and cysteine sulfinic acid (C\({}_{3}\)H\({}_{7}\)NO\({}_{4}\)S)/S-oxocysteine (C\({}_{3}\)H\({}_{7}\)NO\({}_{3}\)S) for H/C = 2.33 have been identified. Line C (light blue line), with a slope of 2, shows entries joined by hydratation or condensation reactions; for instance, steardionic (C\({}_{18}\)H\({}_{28}\)O\({}_{2}\))/hydroxylinolenic (C\({}_{18}\)H\({}_{30}\)O\({}_{3}\)) acids. Finally, compounds in different alkylation series occur along lines D (purple lines) with an intersect at H/C = 2, including the series of fatty acids, such as myristic (C\({}_{14}\)H\({}_{28}\)O\({}_{2}\))/palmitic (C\({}_{16}\)H\({}_{32}\)O\({}_{2}\))/stearic (C\({}_{18}\)H\({}_{36}\)O\({}_{2}\))/arachidic (C\({}_{20}\)H\({}_{40}\)O\({}_{2}\)) acids. Moreover, the donut chart of elemental composition (Figure 2) reports the percentage of different entries identified by the MS analysis. The graph establishes CHO as the most abundant class of compounds (\(>\)50%), mainly represented by fatty acids, polyphenols and terpenoids, followed by CHNO (ca. 28%), including entries such as amino acids, dipeptides, and amides of fatty acids, and by CHNOS (ca. 7%). All other molecular classes (CH, CHN, CHNOP, CHNOPS, CHOP, CHOS) contribute less than 5% each. Figure 1: **(A)** Van Krevelen plot gained from the molecular formulas obtained by ESI FT-ICR MS analysis of LO. **(B)** Van Krevelen diagram displays homology series (dashed lines) related to the following chemical reactions: A lines (green) stand for (de)hydrogenation; B lines (red) stand for oxidation or reduction; C lines (light blue) stands for (de)hydration and condensation processes; D lines (purple) stand for (de)methylation. Direct infusion ESI FT-ICR MS is a powerful method with the ability to provide a comprehensive description of the composition of complex mixtures, through the identification of a huge number of metabolites by a single and fast measurement. Despite this, an accurate quantitative analysis is not feasible, mainly due to possible ion suppression phenomena and different ionization responses of the numerous components present in natural mixtures, thus making the quantification challenging. However, these effects may be neglected for metabolites that belong to the same class, thus showing similar chemico-physical characteristics.