Characterisation of the volatile odorant fraction of aromatic caramel using heart cutting two-dimensional gas chromatography.
Résumé
Odour is one of the main factors contributing to the consumer acceptability of food products. Characterization of odorant compounds thus represents an important challenge for the food industry. Caramel is the resulting product of controlled heat treatment of sugars. Its volatile fraction includes a large number of oxygenated heterocycles as furans and furanones. Due to similar properties, these compounds exhibit similar interactions with the column stationary phase. Consequently, the one-dimensional Gas Chromatography (GC) profile of the volatile fraction of caramel shows numerous co-elutions. The aim of this study was to optimize a two-dimensional chromatographic method with the purpose of identifying odorant compounds in different caramel aroma extracts. Based on the results of a preliminary GC/O study, a classical heart cut GC-GC approach was led to separate compounds from different selected regions of the chromatogram. Simultaneous Mass Spectrometric (MS) and Olfactometric (O) detection at the end of the 2D column allowed the identification of new odorant compounds reported for the first time in caramel. Some compounds were associated to the typical burnt and roasted odour notes found in caramel. Moreover, the use of a cryogenic trap at the start of the 2D column allowed to focus the eluate and to trap the same region during multiple runs. This technique appeared as powerful for the identification of odorants in trace concentrations but which exhibits low odour threshold and which could be relevant for the aroma.