Pleasantness of binary odor mixtures: rules and prediction.

Pleasantness is a major dimension of odor percepts. While naturally encountered odors rely on mixtures of odorants, few studies have investigated the rules underlying the perceived pleasantness of odor mixtures. To address this issue, a set of 222 binary mixtures based on a set of 72 odorants were rated by a panel of 30 participants for odor intensity and pleasantness. In most cases, the pleasantness of the binary mixtures was driven by the pleasantness and intensity of its components. Nevertheless, a significant pleasantness partial addition was observed in six binary mixtures consisting of two components with similar pleasantness ratings. A mathematical model, involving the pleasantness of the components as well as tau-values reflecting components' odor intensity, was applied to predict mixture pleasantness. Using this model, the pleasantness of mixtures including two components with contrasted intensity and pleasantness could be efficiently predicted at the panel level (R2 > 0.80, RMSE < 0.67).