## 4 Discussion
### Identification of Main Fluorophores in Suuflower and Chestnut Honey Samples
\begin{table}
\begin{tabular}{c c l} \hline
**Honey Sample Label** & **Group** & **Main Fluorophores Contributing to Fluorescence Emission (\(\lambda_{\text{ex}}\), nm)** \\ \hline \multirow{4}{*}{S1} & & Vanillic, ferulic, p-coumaric, 4-hydroxybenzoic, and caffeic acids (290); \\  & & p-coumaric and caffeic acids (330); vitamin B9 and quercetin (330-340); vitamin B2 (430); carotenoids (400-500); chlorophylls (670). \\  & & Caffeic, p-coumaric, ferulic acids (270-290) and unknown fluorophore X \\  & & (270-340); vitamin B6; vitamin B3 (330-340). \\ \hline \multirow{4}{*}{CL2} & CL1 & 4-hydroxybenzoic, caffeic, vanillic, feryline, and p-coumaric \\  & & acids (280-290); quercetin (340); chlorophylls (670). \\  & CL2 & 4-hydroxybenzoic, caffeic, vanillic, ferulic, syringic, and p-coumaric \\  & & acids (280-290); quercetin (340); chlorophylls (670). \\  & CL3 & 4-hydroxybenzoic, caffeic, vanillic, ferulic, syringic and p-coumaric \\  & & acids (280-290); quercetin (340); chlorophylls (670). \\  & & Teryptophan, 4-hydroxybenzoic, p-coumaric, vanillic acids, and ferulic \\  & MA1 & 4-hydroxybenzoic, p-coumaric, vanillic acids, and ferulic \\  & & (330). \\  & MA2 & 2 & Teryptophan, 4-hydroxybenzoic, p-coumaric, vanillic acids, and ferulic \\  & & acid/chlorogenic acid (280-290); vitamin B6, vitamin B9, and quercetin \\  & & (330). \\  & MA3 & 4-hydroxybenzoic, p-coumaric, vanillic acids, and ferulic \\  & & acid/chlorogenic acid (280-290); vitamin B6, vitamin B9, and quercetin \\  & & (330). \\  & L1 & Vanillic and syringic acids (280-290); vitamin B9 and quercetin \\  & & (330-340); chlorophylls (670). \\  & AC1 & 4-hydroxybenzoic, p-coumaric, vanillic acids, and ferulic \\  & AC1 & 4-hydroxybenzoic acid (280-290); vitamin B6, vitamin B9, and quercetin \\  & & (330); chlorophylls (670). \\ \hline \multirow{4}{*}{H1} & & & Tryptphan, vanillic, ferulic, syringe, p-coumaric, and o-coumaric acids \\  & & (280-290); vitamin B6, vitamin B9, and quercetin (330); chlorophylls (670). \\  & & 3 & Teryptophan, vanillic, ferulic, syringe, p-coumaric, and o-coumaric acids \\  & SU1 & (280-290); vitamin B6, vitamin B9, and quercetin (330); carotenoids \\  & & (400-500); chlorophylls (670). \\ \hline \multirow{4}{*}{AR1} & & Vanillic, p-coumaric, 4-hydroxybenzoic, ferulic, and caffeic acids (290); vitamin B9, vitamin B6, and quercetin (330-340); chlorophylls (670). \\  & & Low content of vanillic, ferulic, p-coumaric, 4-hydroxybenzoic, and \\  & FH1 & 4 & caffeine acids (290); vitamin B9, vitamin B6, and quercetin (330-340). \\  & IN1 & Vanillic, p-coumaric, 4-hydroxybenzoic, ferulic, and caffeic acids (290); vitamin B9, vitamin B6, and quercetin (330-340); chlorophylls (670). \\ \hline \end{tabular}
\end{table} 
Table 5: Main fluorophores contributing to fluorescence emission of honey samples, divided into four groups, and characteristic spectral features, as described in detail in the following sections. Underlined fluorophores represent the highest contribution to fluorescence emission at the indicated wavelength. The emission spectrum of sunflower honey by exciting at \(\lambda_{\rm ex}>\) 420 nm (Figure 9c) is different from all other honey samples (see also Figure 2c), since it presents a maximum emission at \(\sim\)520 nm and a second local maximum (or emission shoulder) at \(\sim\)480 nm, whose intensity varies sensibly by moving to larger excitation wavelengths. A fluorophore responsible for intense emission centered at 520 nm, with a similar spectral profile to sunflower honey, is vitamin B2 [8, 47, 57]. Moreover, the particular structure and shaped emission band of sunflower honey at excitation wavelengths in the range 400-500 nm (see Figure 9c) are probably due to the presence of self-absorption by carotenoids [42]. This interpretation is in agreement with the presence of large amounts of \(\beta\)-carotene and other carotenoids, such as lutein, in sunflower honey [47], as observed by UV-Vis absorption spectroscopy (see Table 3).