Subjective and Facial EMG Responses to Bitter, Astringent, and Chemesthetic Compounds differ between PROP Super- and Non-Tasters

PROP taster status (PTS) refers to an individual’s perceptual sensitivity to the bitter compound 6-n-propylthiouracil (PROP). It is primarily a genetic phenotype associated with variation in density of fungiform papillae on the tongue. However, the effects of PTS on food preferences go beyond bitter-tastants. For example, significant relationships have been reported between PTS and hedonic responses to chemesthetic and astringent stimuli, though findings are inconsistent and associations not universally observed. Typically, hedonic responses to oral stimuli are assessed using subjective rating scales, which require participants to consciously evaluate their perceptual experience and can be influenced by demand characteristics. In contrast, psychophysiological measures allow for the assessment of objective reactions in real-time, capturing responses without interrupting ongoing behaviours. The aim of the present study was to examine whether subjective ratings or facial electromyography (fEMG) responses, a well-established implicit measure of affect, differ for bitter, chemesthetic, and astringent compounds between PROP super- and non-tasters. Participants were pre-screened for PTS, then, subjective intensity, pleasantness and fEMG responses to caffeine (bitter), menthol (chemesthetic) and alum (astringent) were assessed. Subjectively, super-tasters rated all three stimuli as more intense than non-tasters, but only caffeine elicited significantly lower subjective liking ratings from super-tasters than non-tasters. While corrugator fEMG activity differed between PTS groups in response to bitter caffeine, zygomaticus activity showed group-level differences between super-tasters and non-tasters across all three stimuli. These findings provide support for fEMG as a valuable tool for advancing research on quantifying individual differences in oral sensation and hedonic evaluation.