HS-SPME/GC-MS metabolomic analysis for the identification of exogenous volatile metabolites of monofloral honey and quality control suggestions

In an effort to investigate whether Hellenic honey is favorable to contamination, a metabolomic approach using gas chromatography coupled to mass spectrometry (GC/MS) in combination with headspace solid phase microextraction (HS-SPME) was applied for the analysis of 203 monofloral honey samples of different botanical origin (citrus, fir, pine, and thyme). For semi-quantification purposes, the use of the internal standard method was considered. Results showed that some honey samples had an exogenous volatile profile consisted of four volatile metabolites: dichloromethane, chloroform, cyclohexane and toluene, which are probably contaminants. These volatile compounds were semi-quantified in diverse amounts, and classified in relation to honey botanical origin with the use of chemometrics. Toluene proved to be the major contaminant in, however, a diverse range (0.001-0.163 mg kg(-1)) and frequency of occurrence. Apart from chloroform in which, a zero tolerance maximum residue limit has been proposed in the EU legislation, the study sets the questioning in both national and international authorities to establish the upper limit for some other exogenous volatile compounds identified in honey.