Sensitivity to pyrazines

This is pure speculation Nils, but we and other animals generate these pyrazines and other volatiles all over our bodies (if you followed Python, think "aborigines aaaahmpit"). I believe they are some kind of marker, not unlike pheromones, therefore important in sexual communication, and that they are easily detected by the odorant binding proteins in our nasal mucus. I don't believe TCA is a marker among animals, so we possibly don't detect it as easily.

(Mark, please end this nonsense of mine...)

Avoiding the consumption of ladybirds/ladybugs/coccinella might have helped our ancestors survive:

The above suggests "The sensory threshold for TCA of a few individuals can be measured in the parts per trillion."

So some people (presumably a tiny minority?) have a sensitivity for TCA as good as the rest of us have sensitivity for pyrazines (i.e., parts per trillion = ng/L).

Do these people enjoy wine? Or do they find every wine in contact with cork or wood unpleasant?

It would be interesting to take a group of people and measure their TCA and pyrazine sensitivity (blindly) and then move onto a blind wine tasting (perhaps with some TCA or pyrazine thrown in for good measure!). Perhaps it's already been done. If so, I'd like to read about it.

Take a population sample and bring them to a cork forest (there is one not far from my house if you need one). If they start doing funny things to the tress, they are oversensitive to TCA... :-)

Nils, our threshold of sensitivity to TCA is usually around 3-5 parts per trillion. Given that a liter of water weighs 1 kg, 1 ppt would be 1 ng, so our TCA sensitivity would be 3-5 ng/L -- comparable to that of pyrazines. It's also dangerous to ascribe all behavior as according us an evolutionary benefit. Some may, some may not. Maybe our sensitivity to pyrazines is there to warn us of unripe fruit? ;-)

Mark Lipton

Hmmm - will obviously have to check up on the data concerning TCA sensitivity. I parse Tom's post as a case for pyrazine sensitivity being our way of being warned of lady bugs.

Cheers

Nils

I did some quick searching for pyrazine sensitivity. Below is the abstract to one article I found.

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J Food Sci. 2007 Sep;72(7):S468-72. Determination of ortho- and retronasal detection thresholds for 2- isopropyl-3-methoxypyrazine in wine. Pickering GJ, Karthik A, Inglis D, Sears M, Ker K.

Dept. of Biological Sciences, Brock Univ., 500 Glenridge Ave., St. Catharines, ON L2S 3A1, Canada. snipped-for-privacy@brocku.ca

2-Isopropyl-3-methoxypyrazine (IPMP) is a grape-derived component of wine flavor in some wine varieties as well as the causal compound of the off-flavor known as ladybug taint (LBT), which occurs when Harmonia axyridis beetles are incorporated with the grapes during juice and wine processing. The main objective of this study was to obtain robust estimates of the orthonasal (ON) and retronasal (RN) detection thresholds (DTs) for IPMP in wines of differing styles. The ASTM E679 ascending forced choice method of limits was used to determine DTs for 47 individuals in 3 different wines--Chardonnay, Gewürztraminer, and a red wine blend of Baco Noir and Marechel Foch. The group best estimate thresholds (BETs) obtained for IPMP (ng/L) were Chardonnay, ON: 0.32; Gewürztraminer, ON: 1.56, RN: 1.15, and red wine blend, ON: 1.03, RN: 2.29. A large variation in individual DTs was observed. Familiarity with LBT was inversely correlated with DTs for Gewürztraminer, and no difference in thresholds was observed between winemakers and nonwinemakers. We conclude that the human DT for IPMP is extremely low and influenced significantly by wine style and evaluation mode. We recommend against the reporting of single- threshold values for wine flavor compounds, and encourage the determination of consumer rejection thresholds for IPMP in wine.

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The following article gives a 2 ng/L odor threshold for wine (referencing the second article).

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J Biosci Bioeng. 2005 Aug;100(2):178-83. Identification of 2,4,6-trichloroanisole (TCA) causing a musty/ muddy off-flavor in sake and its production in rice koji and moromi mash. Miki A, Isogai A, Utsunomiya H, Iwata H.

National Research Institute of Brewing, 3-7-1 Kagamiyama, Higashi- Hiroshima 739-0046, Japan. snipped-for-privacy@kzkappa.co.jp

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J Agric Food Chem. 2002 Feb 27;50(5):1032-9. Method for the gas chromatographic assay with mass selective detection of trichloro compounds in corks and wines applied to elucidate the potential cause of cork taint. Soleas GJ, Yan J, Seaver T, Goldberg DM.

Quality Assurance Department, Liquor Control Board of Ontario, 55 Lakeshore Boulevard East, Toronto, Ontario, Canada M5E 1A4.

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In the above, I should have written "The following article gives a 2 ng/L *TCA* odor threshold for wine..."

Yes, 2 ppt (2 ng/L) is the accepted lower threshold of human sensitivity, though more typically people's sensitivities begin at 3-20 ppt. As with many odors, human sensitivity varies greatly from individual to individual.

Mark Lipton