In humans, 25 different hTas2Rs are evolved to bind the bitterants with diverse chemical structures (Behrens and Meyerhof, 2013; Jaggupilli et al., 2016). Some Tas2Rs such as Tas2R10, Tas2R14, and Tas2R46 broadly accommodate the various bitterants, while some Tas2Rs such as Tas2R50 exquisitely select the specific bitterants (Meyerhof et al., 2010; Brockhoff et al., 2011; Ji et al., 2014). At the same time, the promiscuous bitterant can interact with multiple Tas2Rs, while the selective bitterant can only activate one or few specific Tas2Rs (Di Pizio and Niv, 2015). Therefore, the compound that can stimulate at least one Tas2R can be treated as a bitterant, however, only the compound that cannot activate any of 25 hTas2Rs can be defined as a non-bitterant, since a compound cannot stimulate one specific Tas2R, which could still elicit the bitterness via targeting another Tas2R.