The role of odour quality in the perception of binary and higher-order mixtures.

Twenty participants scaled similarities in odour quality, odour intensity and pleasantness/ unpleasantness of 10 binary and 5 higher-order mixtures of 5 odorous degradation products from the polymer Polyamide 6.6. The perceived odour qualities of all binary mixtures were represented well as intermediary vectors relative to their component-odour vectors in a three-component principal components analysis. The odour qualities of the "floral/fruity" 2-pentylcyclopentan-1-one and the "sharp/cheese-like" pentanoic acid contributed profoundly to their binary mixtures, as did the "minty" cyclopentanone, but in fewer cases. Conversely, the "ether-like" 2-methyl pyridine and "nutty" butanamide did not contribute much. Odour similarity was shown to be caused by odour quality, rather than odour intensity. Three out of five degradation products formed distinct clusters of odours and were therefore interpreted to be profound contributors to the odour quality of the binary mixtures. The higher-order mixtures created new odour qualities which were completely different and untraceable to their various parts as perceived alone. These results demonstrate that it is critical to research the perception of natural mixtures in order to be able to understand the human olfactory code.