How consumers sense food is crucial knowledge for a food industry constantly organising the building blocks of new food formulations.
"Information on how food constituents interact with receptors is needed to design and identify inhibitors and enhancers that can be targeted towards specific bitter compounds," said senior author Liquan Huang.
"Our findings may help make health-promoting bitter foods such as broccoli more palatable for children and adults."
Taste is a key driver in the €3.2 trillion global food industry and a greater understanding of the physiology of consumers could lead to strong market advantages.
And the new results, published in the journal Biochemical and Biophysical Research Communications , could lead to practical means of manipulating food flavour in general and bitter taste in particular, suggest the researchers from the Tokyo University of Agriculture and Monell Chemical Senses Center in Philadelphia.
According to background information in the article, the about 25 different human bitter receptors are known from human genome sequences.
Only a few of these bitter receptors can be activated by known chemical compounds, however, leaving many 'orphan receptors' whose activating compounds are still to be identified.
As a result of this, it is unclear how these orphan receptors contribute to bitter taste perception.
According to the new research, a certain type of human bitter receptor (hTAS2R1) was strongly activated by the bitter peptides glycyl-L-leucine (Gly-Leu) and glycyl-L-phenylalanine (Gly-Phe), while no activation for any of the receptors was observed when tested with the non-bitter dipeptide glycylglycine (Gly-Gly).
Such work is important for fermented foods, which typically contain numerous peptides responsible for the bitter taste associated with such food.
"Our results, which showed that bitter peptides stimulated the human bitter receptors hTAS2Rs, support this hypothesis based on human sensory tests that have been conducted by several investigators in the past," wrote the authors.
"These results suggest that humans utilize TAS2Rs to recognize and perceive the structure and bitterness of peptides."
Such a finding opens doors to screening for specific bitter receptor inhibitors, explained Huang.
"Such inhibitors can be used to suppress unpleasantness and thereby increase palatability and acceptance of health-promoting bitter foods, such as green vegetables or soy products," he added.
Scientists have long assumed that bitter taste evolved as a defence mechanism to detect potentially harmful toxins in plants.
Source: Biochemical and Biophysical Research Communications Volume 365, Pages 851-855 "Bitter peptides activate hTAS2Rs, the human bitter receptors" Authors: K. Maehashi, M. Matano, H. Wang, L.A. Vo, Y. Yamamoto, L. Huang