Evaluation of omission testing as a method for identifying important odorants in a mixture

Our goal was to determine whether people could learn to discriminate between a five-compound odor mixture with all compounds at the same perceived intensity and that same mixture with any one of the five compounds removed. We first selected, for each panelist separately, concentrations of each of four compounds that were equivalent in intensity to 5 ppm acetylpropionyl. We then constructed, for each participant, a mixture of the five compounds matched in intensity. Panelists then participated in 20 sessions consisting of a series of A-not-A tests with corrective feedback. Panelists, as a group, were able to discriminate between the full five-compound mixture and mixtures with any one of the five compounds removed after 60 trials. However, low d′ values indicated that the mixtures were extremely difficult to discriminate. Only 60% of the panelists were able to discriminate between the complete mixture and the n-1 mixtures even after 200 trials. Practical applications: When compounds are at a similar perceived intensity, using omission testing, as a method for determining the important odorants in a mixture is very likely to indicate that compounds are not important, when, in fact, they are.