Detection thresholds for quinine, PTC, and PROP measured using taste strips.

In clinical practice, when ability to perceive bitter taste is studied, quinine is preferred to phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) as taste stimulus, because many subjects are genetically non-tasters for PTC/PROP. However, it is poorly known how sensitive anterior (front) and posterior (back) parts of the tongue are to different bitter tastants that are detected by different bitter taste receptors (TAS2Rs). In the present study, we aimed to characterize sensitivity to bitter taste at front and back parts of tongue. We measured thresholds for quinine, PTC, and PROP using the "taste strips", employing seven concentrations of each stimulus both at front and back parts of tongue in 203 healthy participants (56% females, mean age 28 years). Our data confirmed the hypothesis that the inability to perceive quinine was less frequent than the inability to perceive PTC and PROP: People can still perceive the bitter taste of quinine even if they are "non-tasters" for PROP/PTC. As expected, strong correlations between PTC and PROP thresholds were observed. Interestingly, correlations between thresholds for quinine and PTC/PROP also emerged. Overall, the detection thresholds were lower when measured at front part of the tongue. Our data suggest that determining taster status for quinine using paper "taste strips", applied to front part of the tongue, represents a suitable method for the screening for ageusia for bitter taste.