Slight variations in components ratio affect odor pleasantness of a blending mixture
Résumé
Odors rely mainly on the perception of odorants mixtures but are commonly perceived as single undivided entities; nevertheless, the processes involved remain poorly explored. It has been reported that perceptual blending, based on configural olfactory processing, can lead odorant mixtures to give rise to an emergent odor quality not present in the components. Furthermore, very slight variations (just noticeable differences, jnd) in components concentrations were shown to be sufficient to modify the odor quality of a blending mixture. In the present study, we set out to examine whether jnd in components concentrations could also affect the odor pleasantness of a blending mixture. We started from the composition of a ternary target mixture of odorants in which an emergent pineapple odor has been evidenced for a given concentration of each component. Then, we set 4 concentration levels of each component that elicit jnd. Each combination of levels was used to design sample mixtures that were delivered using a dynamic air-dilution olfactometer. Fifteen subjects (3 men, 19 to 26 years old) compared the intensity, typicality, and pleasantness of each sample mixture against the target mixture in a paired-comparison protocol. Statistical modeling of the results showed that slight variations in components ratio did affect significantly odor pleasantness of the ternary mixtures. When the concentration of one of the components increased, the mixture pleasantness decreased whereas an interaction between the two other components was observed. These results underlined (i) the key role of odorants concentrations ratio on the pleasantness of a mixture odor and (ii) the human ability to discriminate between odor percepts induced by mixtures including even close odorant proportions.