Brief communicationTwo decades of supertasting: Where do we stand?
Introduction
Taste is a sentinel of the alimentary tract, preventing the ingestion of toxins and informing the ingestion of nutrients. Given this sentinel function, the evolutionary mechanism behind variation in taste is less clear, although it presumably confers some advantage given the parallel, independent evolution of dimorphic taste phenotypes in human and non-human primates [1]. Reports that humans vary in taste ability date back to 1888 [2]; the next major advance occurred in 1931 with the dual discovery of ‘taste-blindness’ for thiourea compounds [3] and the heritable basis for this trait [4]. Over the next 80 years, differences in detection thresholds were eventually studied hundreds of times across thousands of participants (see [1]). In 2003, allelic variation in the bitter receptor gene TAS2R38 was implicated as the molecular basis of differences in phenylthiocarbamide (PTC) detection thresholds [5], and quickly extended to include propylthiouracil [6].
However, over the past two decades, the study of individual differences in oral sensation has also grown to include the idea of supertasting. Originally identified as the heightened response to the suprathreshold bitterness of concentrated propylthiouracil (PROP) [7], the contemporary view supports that supertasting encompasses elevated response to all taste qualities (e.g., [8], [9]), as well as oral somatosensation [10], [11] and even retronasal olfaction [12]. Examination of molecular genetics in this context indicate TAS2R38 alleles cannot explain supertasting [9]. This makes intuitive sense, as it is hard to envision how polymorphisms in a narrowly tuned bitter receptor gene could mechanistically explain elevated response across multiple taste qualities, oral somatosensation and retronasal olfaction. Thus, present work by Calò et al. [13] represents a promising step forward for the field as the identification of a novel polymorphism that may explain variation in suprathreshold response more broadly is of critical interest. The research by Calò et al. was restricted to propylthiouracil bitterness — it remains to be determined whether this SNP associates with heightened response to other stimuli or with taste papillae or taste bud density.
Section snippets
Two distinct phenotypes for bitterness
PROP supertasters are identified by perceived intensity [7] and not by threshold measures [14]. That is, detection threshold and suprathreshold response (perceived bitterness) are two related but distinct phenotypes [9], [15]. This is a critical distinction, because direct scaling (see [16], [17]) provides a means to measure a range of perceptions that cannot be quantified with threshold tasks based on signal detection theory. This is especially critical for chemosensory response as it relates
Origins of the term supertaster
The term supertaster first appeared in print in a 1991 article by Linda Bartoshuk in the trade journal Food Technology. In her laboratory, Bartoshuk et al. had noticed non-tasters were relatively homogeneous in response, while the tasters were much more variable, including a subgroup who found PROP to be intensely bitter. They called those people ‘supertasters’. This observation was presaged by a rarely cited 1979 report showing a subset of PTC tasters gave high intensity ratings for the
Greater acuity in supertasters
Two converging lines of evidence, one direct and one indirect, suggest supertasting may not be limited to greater orosensory response but may also include greater chemosensory acuity. In particular, supertasters have smaller average Weber fractions for model foods [26]. That is, supertasters are able to discriminate smaller changes in ingredient levels in a forced choice task paradigm, which is consistent with other reports based on suprathreshold methods [11], [20]. The greater acuity
Moving beyond PROP
Although supertasting and PROP bitterness have been largely synonymous (and contentious) for the last two decades, one can gain important insight by carefully distinguishing between the construct of supertasting — heightened orosensory response that is broadly tuned — and its historical operationalism via PROP [9]. Indeed, two non-PROP based measures for identifying individuals with heightened taste response have been reported previously [8], [31]. The first, irritant bitter tasting (iBT), is
Supertasting — the future?
PROP bitterness and the jargon supertasting are so thoroughly enmeshed in both the scientific literature and the public consciousness, that attempting to disentangle them seems nearly impossible. However, elevated responses of TTs and iBTs are independent of PROP bitterness [8], [32], and this raises an important semantic issue: is it appropriate to consider these individuals supertasters? Secondarily, is it possible to be a general supertaster (gST; [39]) while not being a PROP supertaster
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