Headspace solid-phase microextraction-gas chromatography–mass spectrometry characterization of propolis volatile compounds

Abstract

In this study, a novel and efficient method based on headspace solid-phase microextraction (HS-SPME), followed by gas chromatography–mass spectrometry (GC–MS), was developed for the analysis of propolis volatile compounds. The HS-SPME procedure, whose experimental parameters were properly optimized, was carried out using a 100μm polydimethylsiloxane (PDMS) fiber. The GC–MS analyses were performed on a HP-5 MS cross-linked 5% diphenyl-95% dimethyl polysiloxane capillary column (30m×0.25mm I.D., 1.00μm film thickness), under programmed-temperature elution.Ninety-nine constituents were identified using this technique in the samples of raw propolis collected from different Italian regions. The main compounds detected include benzoic acid (0.87–30.13%) and its esters, such as benzyl benzoate (0.16–13.05%), benzyl salicylate (0.34–1.90%) and benzyl cinnamate (0.34–3.20%). Vanillin was detected in most of the samples analyzed in this study (0.07–5.44%). Another relevant class of volatile constituents is represented by sesquiterpene hydrocarbons, such as δ-cadinene (1.29–13.31%), γ-cadinene (1.36–8.85%) and α-muurolene (0.78–6.59%), and oxygenated sesquiterpenes, such as β-eudesmol (2.33–12.83%), T-cadinol (2.73–9.95%) and α-cadinol (4.84–9.74%). Regarding monoterpene hydrocarbons, they were found to be present at low level in the samples analyzed in this study, with the exception of one sample from Southern Italy, where α-pinene was the most abundant constituent (13.19%). The results obtained by HS-SPME-GC–MS were also compared with those of hydrodistillation (HD) coupled with GC–MS.The HS-SPME-GC–MS method developed in this study allowed us to determine the chemical fingerprint of propolis volatile constituents, thus providing a new and reliable tool for the complete characterization of this biologically active apiary product.