Effects of linoleic acid on sweet, sour, salty, and bitter taste thresholds and intensity ratings of adults

Evidence supporting a taste component for dietary fat has prompted study of plausible transduction mechanisms. One hypothesizes that long- chain, unsaturated fatty acids block selected delayed- rectifying potassium channels, resulting in a sensitization of taste receptor cells to stimulation by other taste compounds. This was tested in 17 male and 17 female adult ( mean +/- SE age = 23.4 +/- 0.7 yr) propylthiouracil tasters with normal resting triglyceride concentrations ( 87.3 +/- 5.6 mg/ day) and body mass index ( 23.3 +/- 0.4 kg/m(2)). Participants were tested during two similar to 30- min test sessions per week for 8 wk. Eight stimuli were assessed in duplicate via an ascending, three- alternative, forced- choice procedure. Qualities were randomized over weeks. Stimuli were presented as room- temperature, 5- ml portions. They included 1% solutions of linoleic acid with added sodium chloride ( salty), sucrose ( sweet), citric acid ( sour), and caffeine ( bitter) as well as solutions of these taste compounds alone. Participants also rated the intensity of the five strongest concentrations using the general labeled magnitude scale. The suprathreshold samples were presented in random order with a rinse between each. Subjects made the ratings self- paced while wearing nose clips. It was hypothesized that taste thresholds would be lower and absolute intensity ratings or slopes of intensity functions would be higher for the stimuli mixed with the linoleic acid. Thresholds were compared by paired t-tests and intensity ratings by repeated measures analysis of variance. Thresholds were significantly higher ( i.e., lower sensitivity) for the sodium chloride, citric acid, and caffeine solutions with added fatty acid. Sweet, sour, and salty intensity ratings were lower or unchanged by the addition of a fatty acid. The two highest concentrations of caffeine were rated as weaker in the presence of linoleic acid. These data do not support a mechanism for detecting dietary fats whereby fatty acids sensitize taste receptor cells to stimulation by taste compounds.