## 3 Results and Discussion
### 3D-EEM Spectra of Honey Samples  
Characteristic 3D-EEM spectra for each honey type are presented in Figures 1-4. Honey spectra showed intensities at different \(\lambda\)ex values as follows (Figure 5): aromatic amino acids, including phenylalanine, tryptophan and tyrosine residues (\(\lambda\)ex = 240-280 nm) [17; 23; 34], phenolic compounds (\(\lambda\)ex = 280-330 nm and \(\lambda\)ex = 310-380 nm) [13; 17; 18; 24], Maillard reaction compounds such as furosine and hydroxymethylfurral (HMF) (\(\lambda\)ex = 380-440 nm) [13; 22], and flavins (\(\lambda\)ex = 440-500 nm) [11; 23; 24]. Figure 1: Characteristic 3D-EEM spectra of thyme honey. Figure 4: Characteristic 3D-EEM spectra of citrus honey. Figure 3: Characteristic 3D-EEM spectra of fir honey. Fluorescence spectra of thyme, pine, fir, and citrus honey highlight similar 3D-EEM patterns. Samples were complex due to the presence of several fluorophore compounds with overlapping regions. Therefore, raw fluorescence EEMs spectra cannot lead to the determination of phenolic compounds. Some researchers overcame this difficulty by simultaneously scanning excitation and emission wavelengths (\(\Delta\lambda\)) with synchronous fluorescence spectroscopy [35]. In this study, from 3D-EEM, only the 2D spectra that correspond to phenolic compounds were chosen. Figures 6 and 7 show the emission spectra at \(\lambda\)ex = 330 and 360 nm, respectively. These regions were attributed to phenolic compounds and apparent differences were observed among the different honey varieties. Each emission spectrum from a honey sample can be considered as a fingerprint of phenolic substances. These spectra consisted of concomitant high or low concentrations of heterogeneous phenolic compounds accordingly to the honey's nature. Fluorescence spectra of the phenolic standard compounds provided more details. More specifically, \(\lambda\)ex between 330 to 360 nm was attributed mainly to hydroxycinnamic acids while (\(\lambda\)ex) 330 nm had a significant contribution of other phenyl carboxylic acids. Generally, specific phenolic compounds, particularly hydroxycinnamic and phenyl carboxylic acid derivatives, have been detected in several types of blossom honey, as in the case of thyme honey from Italy [36], Greece [37], and citrus honey from China [38], Italy [39; 40], Iran [41] and Greece [37]. Similar results were obtained for honeydow honey from Germany [42], pine honey from Poland [43] and Greece [37; 44], and fir honey from Greece [37; 44]. Figure 5: The 3D-EEM spectra intensities at \(\lambda\)ex = 240–400 and \(\lambda\)em = 250–640. Several studies have suggested possible correlations between the botanical origin and certain hydroxycinnamic and other phenyl carboxylic acids. [PERSON] et al. (2018) reported a notable variation in the content of phenolic compounds of 19 types of honey from Turkey, with ferulic, homogenistic, gentisic, and protocatechuic acids being the most abundant compared to other phenolics. Specifically, the highest levels of homogenistic acid were obtained from thyme, citrus, and protocatechuic acid from pine honey. In addition, pine honey had a high content of syringe acid. Furthermore, all samples contained a significant amount of gentisic, syringe, 3,4-dihydroxyboxbenzoic, caffe, and ferulic acids. [PERSON] et al. (2018) found differences in phenolic acid fractions among Greek honey extracts. Fir  
Figure 6: Emission spectrum at \(\lambda\)ex 330 nm. Figure 7: Emission spectrum at \(\lambda\)ex 360 nm. and pine honey were richer in protocatechuric acid, whereas the vanillin acid content was found to be higher in thyme honey. [PERSON] et al. [37] observed that protocatechuric, p-hydroxybenzoic, vanillic, caffeic, and p-coumaric acid were the major phenolic acids in 12 honey variants (thyme, pine, fir, citrus) from Greece. Thyme and citrus honey had a lower content of protocatechuric and caffeic acid than pine and fir, and p-hydroxybenzoic acid was the dominant compound in thyme honey.