Perception of wine fruity and woody notes: influence of peri-threshold odorants

Abstract

In order to test the hypothesis that woody odorants at sub- and peri-threshold concentrations could modify the olfactory perception of supra-threshold fruity notes in wine, three binary mixtures of fruity and woody odorants were studied. In these mixtures, a single supra-threshold concentration level, close to the one usually found in wine, was used for the fruity note whereas three peri-threshold concentration levels of the woody note were tested. The ability to discriminate odour stimuli on the basis of the presence or absence of the woody odorants in the mixtures was investigated with a triangular test.

For the three binary mixtures the results showed that subjects were able to differentiate between samples containing a woody odorant at all concentration levels from samples without a woody odorant. These findings confirmed the impact of sub- and peri-threshold components on the olfactory perception of odour mixtures, especially in the case of wine woody odorants.

Introduction

Compounds present above their odour threshold are usually considered as key aroma components in “classical” aroma chemistry, which also holds for wine flavour chemistry (De Wet, 1978). Thus, it is not surprising that only a few studies of sub-threshold components affecting olfactory mixture perception have been reported (Guadagni et al., 1963, Laska and Hudson, 1991, Patterson et al., 1993). In an artificial wine medium, for example, Selfridge and Amerine (1978) studied the effects of masking, addition, and synergism in binary odour mixtures where the two components (ethyl acetate and diacetyl) were mixed in various proportions and concentrations. They observed that even when the compounds are at concentrations below their thresholds in wine, an odour can be perceived as a result of perceptual synergism. This observation was made on the basis of the ratios of the threshold values and their concentrations in the artificial wine medium (OAV: odour activity values). Similar studies on mixtures of tomato juice and methyl sulphide and on whisky imitation solutions, were performed by Guadagni, Miers, and Venstrom (1969) and Salo (1973) respectively. On the basis of OAV calculations, the latter author observed synergistic effects among acids at both sub-threshold and near threshold levels. He also observed synergistic effects among carbonyl compounds, when these components were included in mixtures both above and below their threshold (Salo, 1973). Studying a complex gustatory mixture with up to 24 components representing the four taste qualities (sweet, sour, salty, bitter), Stevens (1997) found that the concentration levels needed to reach detection tended to be higher than those expected under additivity conditions. These findings suggest that some hypo-additivity occurs, when all components are present below their detection threshold level.

Most other studies reporting perceptual interactions at threshold level were based on mixtures where all components were at sub- or peri-threshold concentration levels (Guadagni et al., 1963, Laska and Hudson, 1991, Patterson et al., 1993). Nevertheless, a few studies have dealt with the influence of sub- or peri-threshold aroma compounds added to supra-threshold odour compounds. Thus, Bult, Schifferstein, Roozen, Voragen, and Kroeze (2001) studied the effect of sub- or peri-threshold aroma compound on a supra-threshold apple-like mixture and showed that these components were not detected any better in an apple-like mixture than in isolation. However, in wine, a previous study suggested that the presence of odorants generated by oak wood at a concentration lower than their threshold values might have an impact on the global flavour of the product (Spillman, 1997). Moreover, it has also been observed that when the woody notes dominate, the complexity of the wine flavour decreases (Moio, Schlich, Issanchou, Etiévant, & Feuillat, 1993). This suggests a drastic influence of compounds derived by oak wood (woody notes) on the wine bouquet. In addition, it has been observed that woody notes in wine tend to dominate over the fruity ones in binary mixtures where supra-threshold concentration levels of woody and fruity odorants were mixed (Atanasova et al., submitted for publication).

In this context, the aim of the present study was to investigate whether the sub- or peri-threshold woody odorants of wine play a role in the global perception of the fruity notes, modelled by the fruity esters found in many wines. Thus, several fruity–woody binary mixtures, containing peri- or sub-threshold woody odorant concentration levels mixed with a constant supra-threshold fruity odorant concentration level, were submitted to an olfactory discrimination test.