The Odorant (R)-Citronellal Attenuates Caffeine Bitterness by Inhibiting the Bitter Receptors TAS2R43 and TAS2R46.

The Odorant (R)-Citronellal Attenuates Caffeine Bitterness by Inhibiting the Bitter Receptors TAS2R43 and TAS2R46.

J Agric Food Chem. 2016 Aug 27;

Authors: Suess B, Brockhoff A, Meyerhof W, Hofmann T

Abstract
Sensory studies showed the volatile fraction of lemon grass and its main constituent, the odor-active citronellal, to significantly decrease the perceived bitterness of a black tea infusion as well as caffeine solutions. Seven citronellal-related derivatives were synthesized and shown to inhibit the perceived bitterness of caffeine in a structure-dependent manner. The aldehyde function at carbon 1, the (R)-configuration of the methyl-branched carbon 3, and a hydrophobic carbon chain was found to favor the bitter inhibitory activity of citronellal, e.g. even low concentrations of 25 ppm were observed to reduce bitterness perception of caffeine solution (6 mmol/L) by 32%, whereas (R)-citronellic acid (100 pm) showed a reduction of only 21%, and (R)-citronellol (100 pm) was completely inactive. Cell-based functional experiments, conducted with the human bitter taste receptors TAS2R7, TAS2R10, TAS2R14, TAS2R43, and TAS2R46 reported to be sensitive to caffeine, revealed (R)-citronellal to completely block caffeine-induced calcium signals in TAS2R43-expressing cells, and to a lesser extent in TAS2R46-expressing cells. Stimulation of TAS2R43-expressing cells with structurally different bitter agonists identified (R)-citronellal as a general allosteric inhibitor of TAS2R43. Further structure/activity studies indicated 3-methyl-branched aliphatic aldehydes with a carbon chain of ≥4 C-atoms as best TAS2R43 antagonists. While odor-taste interactions have been mainly interpreted in literature to be caused by a central neuronal integration of odors and tastes, rather than by peripheral events at the level of reception, the findings of this study open up a new dimension regarding the interaction of the two chemical senses.

PMID: 27569025 [PubMed - as supplied by publisher]

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