Advanced instrumental analysis and electronic noses

Since the development of suitable gas chromatographic methods in the 1960s, researchers have been able to identify thousands of volatile compounds in foods, essential oils and fragrances. High-resolution gas chromatography (GC) combined with mass spectrometry (MS) became the key technique used for quantification and identification of flavour compounds. Individual flavours were found to be complex mixtures containing hundreds of compounds in concentrations ranging from percent to trace (nanograms per kilogram) levels. Addditional information is obtained by smelling the GC effluent after its separation. This technique is called GC-sniffing or GC-olfactometry (GC-O). To determine the relative sensorial importance of a volatile compound to the overall flavour, odour activity values are calculated by relating the measured concentration of a compound to its odour threshold. Since this does not work with unidentified and trace compounds, other methods using GC-O for the determination of the specific contribution of gas chromatographically separated compounds have emerged: aroma extract dilution analysis (AEDA), combined hedonic aroma response measurements (CHARM) and OSME (a time-intensity rating method) [1] [2]. These sniffing techniques clearly demonstrated that of all these volatile components only a few contribute to the characteristic odour and only in some cases character-impact compounds could be found. Therefore, the comprehensive identification of all substances is no longer the main goal.