Retronasal Discrimination Between Vapor-Phase Long-Chain, Aliphatic Fatty Acids

Abstract

Retronasal discrimination between vapor-phase fatty acids was tested in 40 participants. Linoleic, oleic, or stearic fatty acids were used in stimulus delivery containers (SDC) at concentrations previously determined to be detectable when presented vapor phase retronasally (Bolton and Halpern in Chem Senses 35:229–238, 2010). For each of these 18-carbon fatty acids, participants received, retronasally, 5 SDC on 2 trials, with 4 of the containers holding, in random order, 1 fatty acid, and the 5th container, a different fatty acid. In addition, for a “negative control”, on two trials, participants received very dilute linoleic acid (0.005%) versus mineral oil. For all trials, the task was to select the one different SDC. It was found that the one different SDC was selected on 83% of the stearic versus linoleic acid trials, 75% of stearic versus oleic acid trials, 58% of linoleic versus oleic acid trials, and 12% of very dilute linoleic acid versus mineral oil trials. An ANOVA found a difference between these distributions, p < 0.0001. Seventy percent of participants discriminated, i.e., selected the 1 different SDC on both trials (chance p = 0.04) between stearic and linoleic acids, 65% discriminated between stearic and oleic acids, and 38% discriminated between linoleic and oleic acids. No participants discriminated on “negative control” trials. These data suggest that retronasal vapor-phase stearic fatty acid is discriminated from vapor-phase linoleic or oleic fatty acids and that oleic and linoleic fatty acids, at concentrations known to be detectable, are discriminated from each other by a substantial minority of participants.