Perceptual Characterization and Analysis of Aroma Mixtures Using Gas Chromatography Recomposition-Olfactometry

Abstract

This paper describes the design of a new instrumental technique, Gas Chromatography Recomposition-Olfactometry (GC-R), that adapts the reconstitution technique used in flavor chemistry studies by extracting volatiles from a sample by headspace solid-phase microextraction (SPME), separating the extract on a capillary GC column, and recombining individual compounds selectively as they elute off of the column into a mixture for sensory analysis (Figure 1). Using the chromatogram of a mixture as a map, the GC-R instrument allows the operator to “cut apart" and recombine the components of the mixture at will, selecting compounds, peaks, or sections based on retention time to include or exclude in a reconstitution for sensory analysis. Selective recombination is accomplished with the installation of a Deans Switch directly in-line with the column, which directs compounds either to waste or to a cryotrap at the operator's discretion. This enables the creation of, for example, aroma reconstitutions incorporating all of the volatiles in a sample, including instrumentally undetectable compounds as well those present at concentrations below sensory thresholds, thus correcting for the “reconstitution discrepancy" sometimes noted in flavor chemistry studies. Using only flowering lavender (Lavandula angustifola ‘Hidcote Blue’) as a source for volatiles, we used the instrument to build mixtures of subsets of lavender volatiles in-instrument and characterized their aroma qualities with a sensory panel. We showed evidence of additive, masking, and synergistic effects in these mixtures and of “lavender' aroma character as an emergent property of specific mixtures. This was accomplished without the need for chemical standards, reductive aroma models, or calculation of Odor Activity Values, and is broadly applicable to any aroma or flavor.

Volatile and sensory profiling of cocktail bitters

“…Chida et al used cross-matching tests and correspondence analysis to determine which citrus-related compounds were more representative of lemon, orange, and sudachi fruits (Chida, Yamashita, Izumiya, Watanabe, & Tamura, 2006); in some cases, the most representative compounds for each fruit were only present in that fruit, such as citral in lemons; in other cases, compounds which sensorially were particularly representative for one type of fruit were present in all three fruits, such as alpha-pinene for sudachi aroma, or linalool for orange. Again, characteristic qualities of these plants or products may have a significant contribution from mixing effects, as well (Francis & Newton, 2005;Johnson, Hirson, & Ebeler, 2012).…”

Review of the role and methodology of high resolution approaches in aroma analysis

“…Williams et al [22] proposed a GC-pedestal olfactometer (GC-PO) to study odour interaction with other compounds in a mixture, so that synergistic, antagonistic (suppression) or additive effects can be assessed. More recently, perceptual characterisation and analysis of aroma mixtures was studied using GC recomposition-olfactometry (GC-RO) [23]. With microfluidic flow-switching and cryotrapping operations in-line at the end of the GC column as illustrated in Fig.…”

“…The coffee perception in Pinotage wines is the result of a synergistic effect of combined furfural and 2-furanmethanol in which neither of the individual compounds was responsible for the characteristic aroma. Such an approach conveniently generates aroma mixtures consisting of desired combinations as opposed to the recomposition study of Johnson et al [23] which operated according to a flow-switching regimen.…”

“…The present flow switching techniques for solute transfer has enabled the possibility of online volatile recombination studies for synergistic aroma effects [23,47,48,101], that would be extended to troubleshooting of aroma-directed sensory analysis, [48] as well as understanding of the 'smell images' and the flavour perception system in the human brain [102]. This presents a new direction for olfactometry in flavour interaction chemistry, based on mixtures of compounds rather than individual component investigations.…”

Origins of Grape and Wine Aroma. Part 2. Chemical and Sensory Analysis

“…A recent modification of GC-O allows individual peaks or groups of peaks to be selectively recombined as they elute off the column and smelled as a mixture (Johnson et al 2012). The GC-recomposition olfactometry (GC-R) technique allows the creation of aroma reconstitutions without the need for chemical standards or reductive aroma models.…”