Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography

doi:10.1016/j.chroma.2005.05.094

Journal of Chromatography A

Volume 1086, Issues 1–2, 9 September 2005, Pages 99-106

https://doi.org/10.1016/j.chroma.2005.05.094 Get rights and content

Abstract

The practicability and potential of comprehensive two-dimensional gas chromatography (GC × GC) coupled to both conventional flame ionisation (FID) and time-of-flight mass spectrometric (TOF-MS) detection, were compared with those of conventional one-dimensional (1D) GC, with the determination of flavour compounds in butter as an application. For polar flavour compounds, which were collected from the aqueous fraction of butter by means of solid-phase extraction (SPE), it was found that GC × GC dramatically improves the overall separation. Consequently, quantification and preliminary identification based on the use of ordered structures, can be performed more reliably. The improvement effected by replacing 1D-GC by GC × GC is considerable also in the case of TOF-MS detection, as illustrated by the high match factors generally obtained during identification. GC × GC was also used successfully for the characterisation of volatile flavour compounds in the headspace of butter collected by solid-phase microextraction (SPME) and to study the effect of heat treatment on the composition of butter samples in more detail.

Introduction

Several years ago, we studied the trace-level determination of flavour compounds in butter by means of gas chromatography–mass spectrometry (GC–MS) [1]. The study dealt with the volatile flavours present in the aqueous fraction of butter, and pre-treatment was by means of solid-phase extraction (SPE). Five well-known test analytes were used which represented various classes of compounds, some of which may be found in butter: diacetyl (ketones), furaneol (furanones), maltol (pyranones), sotolon (furanones) and vanillin (benzaldehydes). Generally speaking, the results were quite encouraging: the analytical performance characteristics were fully satisfactory for all target analytes except diacetyl (baseline subtraction and selected ion monitoring required). The effect of heat treatment on sample composition could be demonstrated convincingly, some 20 further compounds could be identified (although there were also a number of distinct failures) and quantification at the 0.1–10 mg/kg level did not cause serious problems.

Today, re-reading of the quoted paper rapidly shows that – next to the problems regarding failed quantification and/or identification already mentioned – the unresolved baseline envelope clearly present in the chromatograms of at least some of the test samples strongly suggests that a more powerful separation technique should be used: comprehensive two-dimensional gas chromatography (GC × GC) with either non-selective flame ionisation (FID) or, if required, selective time-of-flight mass spectrometric (TOF-MS) detection [2], [3], [4], [5], [6]. In order to enable a straightforward comparison of the two methods of analysis, conventional (i.e. one-dimensional, 1D) GC and GC × GC, the same general set-up was used as in the earlier study, and the same target analytes and experimental parameters (heat treatment and storage effects) were used. As an extension, the headspace of the butter samples was analysed (by means of solid-phase microextraction, SPME) next to the aqueous fraction.

Section snippets

Analytes and samples

Methyl acetate (J.T. Baker, Deventer, The Netherlands) was freshly distilled and HPLC-grade water was prepared in a Mili-Q (Millipore, Bedford, MA, USA) filtration system. Helium, used as carrier gas (99.999% purity) was supplied by HoekLoos (Schiedam, The Netherlands). Vanillin and diacetyl were from Fluka (Zwijndrecht, The Netherlands), maltol and furaneol from Acros (Geel, Belgium), and sotolon from Aldrich (Brussels, Belgium). Standard solutions of all flavours were prepared at a

SPME

The optimization of the SPME conditions was performed by studying the parameters listed in Table 1. To this end, next to a solution of the five target analytes in water (each at 1 μg/ml), butter samples spiked with the five target analytes (each at 1–5 μg/g) were used. All experiments were performed under stirring to enhance the release of the analytes into the headspace. A short discussion of the experimental findings is given below.

Four commercial fibres were tested, PDMS, Carboxen/PDMS,

Conclusions

GC × GC coupled to both conventional flame ionisation and time-of-flight mass spectrometric detection, is a powerful separation and identification technique for the analysis of complex mixtures of compounds such as are often found in food samples. With the determination of flavours in butter as an example, the improved performance of GC × GC compared with 1D-GC is demonstrated. The main advantages are a more reliable analysis of target compounds, the rapid recognition of prominent classes of

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Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography

Abstract

Introduction

Section snippets

Analytes and samples

SPME

Conclusions

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A