## 2 Results and Discussion
### Volatiles Isolated by Ultrasonic Solvent Extraction  
The volatile organic composition results of the samples obtained by ultrasonic assisted extraction (USE) with two solvents followed by GC and GC/MS analysis are presented in Table 2. A representative TIC chromatogram is presented in Figure 1. The most striking difference among the samples was the concentration of 5-hydroxymethylfurfurral (5-HMF). Sample I collected in 2005 contained 42.5% of 5-HMF (solvent A) and 64.2% (solvent B), respectively, in contrast to sample II from 2009 with percentages of 4.7% (solvent A) and 6.2% (solvent B). The percentage of 5-HMF in both samples was higher in the more polar solvent dichloromethane. Such a high content was expected since 5-HMF is generated during honeybee storage at room temperature. Prolonged storage of the honeybee led to compositional changes due to caramelization of carbohydrates, Maillard reactions, and decomposition of fructose in relative acid medium of the honeydew [10]. These reactions lead to the formation of HMF or other furan/pyran compounds (such as 2-furan methanol (1.7%; 0.3%), 5-methylfurfurral (1.5%; 0.5%), 1-(2-furyl)-2-hydroxyethanone (5.5%; 4.6%), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (1.3%; 0.3%)). Several furan/pyran derivatives were present in the other sample such as 2-furanmethanol (3.0%; 3.7%), 1-(2-furyl)-2-hydroxyethanone (5.1%; 8.8%), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (2.8%; 4.3%). Although the percentage of 5-HMF predominated in sample I, botanical-origin important compounds were notable, as in sample II. \begin{table}
\begin{tabular}{l l c c} \hline
13. & Phenylacetaldehyde\({}^{\text{a}}\) & 1048 & 2.0 & 1.5 \\
14. & _trans_-Linalool oxide (furan type) & 1076 & 18.1 & 13.8 \\
15. & Methyl 2-fluoroate & 1084 & - & 2.8 \\
16. & _cis_-Linalool oxide (furan type) & 1091 & 10.8 & 14.0 \\
17. & Hotrienol & 1106 & 4.4 & 9.7 \\
18. & 2-Phenylethanol\({}^{\text{a}}\) & 1116 & 3.5 & 6.0 \\
19. & 3,5,5-Trimethyl-cyclohex-2-en-1-one & 1124 & 0.6 & - \\
20. & 2-Ethylhexanoic acid & 1140 & 2.9 & - \\
21. & Neroloxide & 1162 & 2.1 & - \\
22. & Epoxylinalool & 1178 & 4.4 & 2.0 \\
23. & Octanoic acid\({}^{\text{a}}\) & 1190 & 8.5 & 9.4 \\
24. & Lilac alcohol (isomer I) & 1208 & 0.8 & - \\
25. & Lilac alcohol (isomer II) & 1237 & 1.3 & - \\
26. & Ethyl phenylacetate & 1253 & 1.2 & - \\
27. & Nonanoic acid\({}^{\text{a}}\) & 1273 & 2.8 & 4.7 \\
28. & Methyl cinnamate & 1312 & 1.1 & - \\
29. & Decanoic acid\({}^{\text{a}}\) & 1370 & 1.5 & 2.4 \\
30. & Hexadecanoic acid\({}^{\text{a}}\) & 1963 & 3.7 & 3.8 \\ \cline{3-3} \cline{3-3} \cline{3-3}  & Total identified & 89.8\% & 86.7\% \\ \hline \end{tabular}
\begin{tabular}{l} RI = retention indices on HP-5 MS column; - = not identified; \({}^{\text{a}}\) – identification confirmed with reference compound; \({}^{\text{a}}\) - tentatively identified; \({}^{\text{a}}\) - correct isomer not identified. \\ \end{tabular}
\end{table} 
Table 1: _Cont._  
honey [2]. The most abundant derivative was phenylacetic acid in sample I (8.1%; 4.7%) and sample II (16.4%; 11.6%) with more pronounced percentages in solvent A. This compound was not found in Spain oak honeydew which may be the consequence of the use of a different extraction technique [2]. Other abundant benzene derivatives were benzoic acid, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, 4-hydroxybenzoic acid, 4-hydroxycinnamic acid and methyl syringae, also not identified in Spain oak honeydew. However, none of the identified benzene derivatives can be proposed as specific markers for oak honeydew since they are present in different honeys.