Activation of human bitter taste receptors by polymethoxylated flavonoids.

Tangeretin and nobiletin are polymethoxylated flavonoids in citrus peel. Both tangeretin and nobiletin are bitter; however, their bitterness has not been evaluated using human bitter taste receptors (hTAS2Rs). We screened 25 kinds of hTAS2Rs and found that hTAS2R14 and hTAS2R46 received both compounds.

The human bitter taste receptor hTAS2R39 is the primary receptor for the bitterness of theaflavins.

We purified several hundred mgs of four major theaflavins (theaflavin, theaflavin-3-O-gallate, theaflavin-3'-O-gallate, and theaflavin-3,3'-O-digallate). Among the 25 hTAS2Rs expressed in HEK293T cells, hTAS2R39 and hTAS2R14 were activated by theaflavins. Both hTAS2R39 and hTAS2R14 responded to theaflavin-3'-O-gallate.

Activation of the hTAS2R14 human bitter-taste receptor by (-)-epigallocatechin gallate and (-)-epicatechin gallate.

Tea catechins have strong bitterness and influence the taste of tea. Among the 25 human bitter-taste receptors (TAS2Rs), we found that hTAS2R14 responded to catechins, in addition to hTAS2R39, a known catechin receptor. Although hTAS2R14 responded to (-)-epicatechin gallate and (-)-epigallocatechin gallate, it did not respond to (-)-epicatechin and (-)-epigallocatechin.