Orthonasal and Retronasal but not Oral-Cavity-Only Discrimination of Vapor-Phase Fatty Acids

Discrimination of vapor-phase linoleic, oleic, and stearic fatty acids was studied using triangle tests. For each trial, 2 of the 3 modified odorant delivery containers (MODCs) had the same content and 1 was different. Contents were either mineral oil-diluted linoleic or oleic acids, with mineral oil in the other MODC (blanks) or undiluted stearic acid with NaCl in the other MODC (blanks). The task was to indicate which of the 3 MODC had the most different odor. Vapor-phase fatty acids and blanks were presented orthonasally, retronasally, or oral-cavity-only. It was found that all 3 fatty acids were discriminated from the blanks both orthonasally and retronasally, P < 0.01, one-tailed binomial tests. Orthonasally, 87% of 30 participants discriminated linoleic acid from blanks and 83% discriminated oleic and stearic acids. Retronasally, 93% discriminated linoleic acid from blanks, 57% discriminated oleic acid; 83% discriminated stearic acid. In contrast, with oral-cavity-only presentations, none of the fatty acids were discriminated from blanks, P > 0.05 (30% of 30 participants discriminated linoleic acid from blanks, P = 0.71; 47%, oleic and stearic acids, P = 0.09). These results demonstrate that human participants can discriminate linoleic, oleic, and stearic fatty acids both orthonasally and retronasally, confirming that humans can smell fatty acids.