## 4 Discussion
Direct hydroxylation of linalool forms (_E_)-8-hydroxylinalool that can be transformed via (_E_)-8-oxolinalool by the enzymatic \(\omega\)-oxidation to lilac alcohols that, by further oxidation, yield lilac aldehydes [78]. Alternatively, epoxidation of linalool produces 6,7-epoxylinalool, which undergoes further reactions to form isomeric furanoid linalool oxides and anhydrolinalool oxides, can further yield lilac alcohols. Terpenes were the most abundant headspace volatiles in _P. mahaleb_ honey [79] such as linalool (4.0-6.6%), three isomers of lilac aldehyde (1.0-11.7%), three isomers of lilac alcohol (0.1-1.2%), and _cis_- and _trans_-linalool oxide (0.6-3.1%). However, from these compounds, only traces of _cis_- and _trans_-linalool oxide were found among essential oil from flowers, leaves, bark and wood of _P. mahaleb_[80]. Conversely, linalool derivatives were not found in _P. avium_[81]. Lower percentages of lilac aldehydes and alcohols were found in _Salix_ spp. honey [82]. Verbenone, bicyclic monoterpenes with pinane skeletons were identified with significant percentages in _Salix_ spp. and _Quercus_ spp. bee pollen from CR. It was found previously in _Salix_ spp. honey headspace at a lower abundance [78]. 6-Methyllhept-5-en-2-one is a frequently reported natural product [83] and can be viewed as degraded terpenoid compound. It was found almost in all samples, particularly in _R. acris_ and _F. excelsior_ bee pollen from CR. Several monoterpenes were found as minor constituents in _P. sylvestris_ bee pollen headspace, such as \(\alpha\)-pinene, \(\beta\)-pinene, \(\delta\)-3-carene, \(p\)-cymene, or \(\gamma\)-terpinene. Those compounds are well-known, major constituents of the essential oil of _P. sylvestris_[84]. (_E_)-geranyl acetone in _F. excelsior_ and _R. acris_ bee pollen headspace and diterpene (_E_,_E_)-geranyl linalool was predominant in _R. acris_. Bee pollen represents a complex organic mixture of various polymeric molecules with predominant constituents covering all major classes of biological macromolecules-proteins, lipids and carbohydrates. Such compositional complexity reflects in a complex FTIR-ATR spectrum of bee pollen exhibiting a broad variety of molecular vibrations characterized by numerous overlapping spectral features. The first valuable insight into the bee pollen IR spectrum was reported by [PERSON] et al. [11], who reported on the usefulness of this technique for studying overall chemical composition of bee pollen. Further investigations covered analysis of uniforal rape bee pollen [24], bee pollen of 13 botanical families and 17 genus [25], and investigation of uniforal Romanian bee pollen [26]. The most comprehensive one was provided by [PERSON] et al. [25], who conducted insightful research on morphological, physico-chemical and spectroscopic properties of uniforal bee pollen. Mentioned authors have provided various assignations for the same absorption bands occurring in the bee pollen IR spectrum, many of which were unspecific or incomplete, i.e., described in a pooled form without clearly assigning the particular band to a corresponding molecular vibration. An example for this is a description of three absorption bands occurring in the spectral region between 1700 and 1500 cm\({}^{-1}\) were previously described as cellulose and protein-relating regions [24; 25; 26]. Significant contribution of cellulose and hemicellulose in the overall spectral features cannot be expected considering the insignificant amount of these constituents in the total composition of bee pollen. Several incorrect assignations have also been provided, such as ketone- and quinine-related assignations [26]. In this study, the formerly described assignations were complemented, and overlapping spectral effects have been additionally explained and elucidated based on the comparative overview of spectral data in relation to physico-chemical measurements (protein, lipid and sugar content).