## 3 Results
### The Headspace Composition of Unifloral Bee Pollen  
The headspace (HS) bee pollen volatile organic compounds (VOCs) were determined by headspace solid-phase microextraction followed by gas chromatography and mass spectrometry analysis (HS-SPME/GC-MS) by using DVB/CAR/PDMS fiber. Since the bee pollen VOCs are located in pollenkit, the temperature of 60 \({}^{\circ}\)C was used for HS-SPME to overcome slow volatilization as the consequence of the presence of lipids in pollenkit, such as mono-, di- and triglycerides, which can retard the emission of volatiles. Remarkable differences were found among the bee pollen HS VOCs. The bee pollen collected by the honey bees from CR were the most diverse among all locations and collecting periods, including the bee pollen from _R. acris_ L., _F. excelsior_ L., _P. sylvestris_ L., _A. schoenoprasum_ L., _C. biennis_ L., _J. regia_ L., _Quercus_ spp., _A. hippocastanum_ L. and _Salix_ spp. (Table 3). (\(E\),\(E\))-Geranyl linalool (49.27%) prevailed in _R. acris_ bee pollen HS VOCs along with (\(E\))-geranyl acetone (5.46%). Two other abundant compounds were 6-methylhept-5-en-2-one (12.39%) and nonanal (8.92%). Principal components of _F. excelsior_ bee pollen headspace were 6-methylhept-5-en-2-one (21.45%), (\(E\))-geranyl acetone (16.19%) and nonanal (15.22%). Nonanal (46.70%) predominated in HS VOCs of _P. sylvestris_ bee pollen. Several monoterpenes were found as minor constituents such as \(\alpha\)-pinene, \(\beta\)-pinene, \(\delta\)-3-carene, \(p\)-cytmene, \(\gamma\)-terpinene as well as decanal. Benzaldehyde (29.11%), nonanal (14.38%), pentadecane (9.63%) and cyclopent-2-ene-1,4-dione (6.14%) were leading compounds of _A. schoenoprasum_ bee pollen headspace. _C. biennis_ bee pollen headspace mainly contained hexanoic acid (24.46%) and heneicosane (20.17%), followed by nonanal (8.37%), octanoic acid (8.78%), acetoin (5.06%) and hexanal (4.59%). Nonanal (59.76%) dominated in HS VOCs of _J. regia_ bee pollen, followed by hexanal (7.34%), 6-methylhept-5-en-2-one (8.61%) and (\(E\))-\(\beta\)-ocymene (5.04%). The major compound of HS VOCs of _Quercus_ spp. bee pollen was benzaldehyde (40.34%) and verbenone (13.11%), followed by nonanal (6.98%) and other lower aliphatic compounds. Butanal (20.96%) and benzaldehyde (18.68%) were principal constituents of HS VOCs of _A. hippocastanum_ bee pollen. Other abundant compounds were 3-methylbutanal (8.85%), hexanal (5.40%), 2-ethylhexan-1-ol (6.15%) and nonanal (7.84%). Benzaldehyde (27.46%) also prevailed in HS VOCs of _Salix_ spp. bee pollen, followed by berbenoene (21.44%). The samples from MR contained the bee pollen of _P. avium_ L., _Salix_ spp., _T. officinala_ L., _P. sylvestris_ L., _C. biennis_ L., and _Q. pubescens_ (Table 4). The bee pollen composition is completely different than in CR due to various plants distribution. Lilac aldehydes were the major compounds of _P. avium_ bee pollen headspace: ilac aldehydes (A 14.84%, B 29.30% and D 13.37%) followed by ilac alcohols (A 11.37%, B 13.76% and D 4.21%). HS VOCs of _Salix_ spp. bee pollen contained mainly 3-hydroxybutan-2-one (5.47%), pentanal (4.14%), hexanal (7.02%), heptanal (5.17%) and nonanal (9.28%). Another abound group of compounds belongs to ilac aldehydes (A 6.06%; B 10.43% and D 3.94%). Pentadecane was also abundant with 10.29%. Lower aliphatic compounds were abundant in _T. officinal_ bee pollen headspace being dominated by 3-methylpentanal (10.37%), 2-methylbutanal (5.42%) and 3-methylbutanal (4.57%). Another major compound was benzaldehyde (28.98%). Lilac alcohols were present at minor percentages (A 3.85%. B 6.42% and D 2.48%). The predominant compound in HS VOCs of _P. sylvestris_ bee pollen was pentadecane (51.16%). Other abundant compounds were acetic acid 10.10%, ethanol 6.93%, \(\beta\)-phellandrene (5.69%) and nonanal (8.09%). HS VOCs of _C. biennis_ bee pollen mainly constituted hereicosane (18.23%), acetic acid (21.34%), acetoin (11.87%) and ethanol (7.17%). Lower percentages of benzaldehyde and phenylacetaldehyde were found.