Determination of chemosensitivity to free fatty acids in humans

The purpose of the present investigation was to determine gustatory sensitivity to free fatty acids in humans. Preliminary psychophysical data in humans indicate that long-chain fatty acids of varying saturation are effective taste stimuli. This is consistent with electrophysiological and animal data attributing a gustatory component to free fatty acids. The present study sought to isolate the taste property of three 18-C fatty acids by masking other sensory attributes and used detection thresholds obtained from college-age students to determine sensitivity to oil-in-water emulsions. Due to a heightened awareness of fat-containing foods among individuals both sensitive to 6-n-propylthiouracil (PROP) and physically fit, all participants were physically fit and sensitive to PROP. Linoleic, oleic, and stearic fatty acids were sonicated in deionized water in concentrations ranging from 0.00028%–5% (w/v). To minimize oxidation, samples were stored under nitrogen. Stimuli were prepared fresh daily and 0.01% EDTA (w/v) was added to each sample. The contribution of viscosity was minimized by addition of 5% Acacia (w/v) to the vehicle. Lubricity effects were reduced by addition of 5% mineral oil (w/v). Olfactory and visual cues were eliminated by having participants wear nose clips and conducting testing under red light. Capsaicin desensitization addressed chemesthetic cues imparted from fatty acids. Oxidized linoleic acid was also included among the test stimuli in order to determine if an oxidation product was an effective stimulus. A three-alternative, forced-choice ascending concentration presentation procedure was employed to obtain detection thresholds. The criterion stopping rule was three consecutive correct identifications of a target sample. Incorrect identification resulted with presentation of the next higher fatty acid concentration. The mean detection threshold for linoleic acid was 0.032 ± 0.007%, for oleic acid 0.022 ± 0.003%, for stearic acid 0.032 ± 0.005% and oxidized linoleic acid 0.025 ± 0.005%. The results provide evidence for a gustatory component to fat perception in humans