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Edited by Stephen D. Roper, Miller School of Medicine, University of Miami, Miami, FL, and accepted by the Editorial Board August 15, 2013 (received for review January 13, 2013)
Significance
Off-flavor substances generated naturally in foods/beverages deteriorate the quality of products considerably. Generally, it has been thought that off-flavor substances induce unpleasant smells exogenously. Here, however, we show that 2,4,6-trichroloanisole (TCA), known as one of the strongest off-flavors, inhibits ciliary transduction channels. Surprisingly, suppression was caused with 1-aM solution. The TCA effect showed slow kinetics, with an integration time of approximately 1 s, and positively correlated with the partition coefficient at octanol/water boundary (pH 7.4) of derivatives. These results indicate that the channels are inhibited through a partitioning of those substances into the lipid bilayer of plasma membranes. Furthermore, TCA was detected in varieties of foods/beverages surveyed for odor losses and is likely to be related to the reduction of flavor.
Abstract
We investigated the sensitivity of single olfactory receptor cells to 2,4,6-trichloroanisole (TCA), a compound known for causing cork taint in wines. Such off-flavors have been thought to originate from unpleasant odor qualities evoked by contaminants. However, we here show that TCA attenuates olfactory transduction by suppressing cyclic nucleotide-gated channels, without evoking odorant responses. Surprisingly, suppression was observed even at extremely low (i.e., attomolar) TCA concentrations. The high sensitivity to TCA was associated with temporal integration of the suppression effect. We confirmed that potent suppression by TCA and similar compounds was correlated with their lipophilicity, as quantified by the partition coefficient at octanol/water boundary (pH 7.4), suggesting that channel suppression is mediated by a partitioning of TCA into the lipid bilayer of plasma membranes. The rank order of suppression matched human recognition of off-flavors: TCA equivalent to 2,4,6-tribromoanisole, which is much greater than 2,4,6-trichlorophenol. Furthermore, TCA was detected in a wide variety of foods and beverages surveyed for odor losses. Our findings demonstrate a potential molecular mechanism for the reduction of flavor.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: hiroko{at}bpe.es.osaka-u.ac.jp.
Author contributions: T.K. designed research; H.T. performed cell experiments; H.K. performed human sensory research; H.T. and T.K. analyzed data; H.K. contributed new reagents/analytic tools; and H.T. and T.K. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. S.D.R. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1300764110/-/DCSupplemental.
Freely available online through the PNAS open access option.
Potent inhibitor of olfactory signal transduction
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