Supertasting and PROP bitterness depends on more than the TAS2R38 gene

Abstract

Polymorphisms in the TAS2R38 gene provide insight to phenotypes long associated 6-n-propylthiouracil (PROP) and phenylthio-carbamide bitterness. We tested relationships between TAS2R38 genotype, taste phenotype, and fungiform papillae (FP) num-ber in 139 females and 59 males (age range 21–60 years), primarily of European ancestry. DNA was analyzed for 3 polymorphic sites, identifying common (alanine–valine–isoleucine [AVI/AVI], heterozygotes, proline–alanine–valine [PAV/PAV]) and rare (proline–valine–isoleucine, alanine–alanine–valine, AAI) forms. Individuals with PROP threshold>0.15 mM were almost exclu-sively AVI/AVI; those with threshold<0.1 mM could have any genotype. PAV/PAVs were more difficult to identify with PROP taste measures, although perceived bitterness of moderate PROP concentrations (0.32, 1 mM) had better correspondence with ge-notype than did threshold. For AVI/AVIs, increases in bitterness from 1 to 3.2 mM PROP nearly paralleled those of TAS2R38 heterozygotes and PAV/PAVs. Some bitterness gains were related to FP number sampled from a standard area on the tongue tip, yet the PROP bitterness–FP relationship differed across genotype. Among homozygotes, FP was a significant determinant of PROP bitterness; heterozygotes showed a flat relationship. Those tasting concentrated PROP as more bitter also tasted concen