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Oh Nuts: Bad Pine Nuts Leave Behind Bitter Taste For Weeks

This past weekend, I was on the hunt for some pine nuts. They’re not always easy to find in the grocery store, and they are almost always expensive. But I love them so—the delicious prize is always worth the aggravation of the search.

Credit: Flickr user Eating The Week

When I finally came upon the pine-nut container in a crowded aisle at the store, I checked to see where the small edible seeds were from. “India,” the container said. And I breathed a sigh of relief.

The reason for my nut-origin prejudice is a condition known as “pine mouth,” or “pine nut syndrome.” At a party earlier this year, a new acquaintance was delighting people clustered around her with what I thought sounded like a fantastical story of bad pine nuts from China inducing a bitter taste in people’s mouths for weeks after their ingestion.

In this case, though, I was wrong to poo-poo the tale. A paper from the Journal of Agricultural & Food Chemistry recently came across the Newscripts desk in which researchers from Germany, Russia, and Belgium banded together to devise a way to sort good pine nuts from taste-altering bad ones. And most of the bad nuts happen to be from China.

Delicious, delicious pine nuts. Credit: Flickr user Culinary Cory

About one to three days after ingesting a bad pine nut, the victim develops a bitter, metallic taste in his or her mouth that lasts “for some days up to two weeks,” says Dirk W. Lachenmeier, the lead author of the JA&FC paper.

Lachenmeier, who works at the Chemical & Veterinary Investigation Agency in Karlsruhe, Germany, says he got interested in pine nut syndrome when several nut samples, accompanied by consumer complaints, arrived at his institute. His agency is one of a series of state-run facilities in Germany that are the authorities on food control.

Initially, Lachenmeier and his team searched for a cause for pine mouth—a specific culprit compound. Unsuccessful, they instead devised a method based on NMR spectroscopy to weed out the naughty nuts. The researchers looked at 57 samples total, from China, Italy, Pakistan, Spain, Turkey, and the Mediterranean, and found in almost every situation where the nuts caused pine mouth that the samples had come from a species of pine tree called Pinus armandii. China happens to frequently harvest seeds from this nontraditional pine species. But Lachenmeier and team also found two other pine-mouth-inducing P. armandii samples, from Spain and the Mediterranean.

When the researchers analyzed both their 1H NMR and 13C NMR data sets with principal component analysis, they saw that all the P. armandii samples—not all of them positive for pine mouth—clustered on the negative end of the scatter plot. A negligible number of normal samples clustered there too, but most of the normal pine tree species—P. pinea and P. gerardiana—had positive principle component values. The method seems to separate the nuts based on their botanical origin.

One company already using this method to assess the quality of pine nuts is Nestlé, according to Frédéric Destaillats of the Nestlé Research Center, in Lausanne, Switzerland. “This allows us to make sure that consumers will not experience pine nut syndrome with our products,” he says.

However, Destaillats emphasizes that “it should not be generalized that all pine nuts exported from China cause taste disturbance.” The country also exports nuts obtained from P. koraiensis, “and this type of pine nut is perfectly safe,” he adds.

As for what actually causes pine mouth, hypotheses abound. One is that a bioactive compound in the nuts increases bile production in the liver. Bile helps break down lipids—which pine nuts are full of—in the small intestine. Most of the time, a process called enterohepatic recirculation occurs, where bile acids circulate from the liver to the small intestine and back again. This “dramatically extends the residence time of many chemicals or drugs present in the digestive tract,” Lachenmeier and team write in their paper, explaining why the hypothesis correlates well with the long duration of pine nut syndrome. One bioactive that has been proposed as the culprit is linalool-oxide, an oxidized terpene fragrance compound.

“Another possibility is that the compound or compounds responsible for pine nut syndrome might be generated during the transport or storage of the finished products,” Destaillats says. “A proper route-cause analysis is required to understand this issue and will need to take into consideration the entire process chain from forest to supermarket.”

In the meantime, I’ll continue to feel for the taste testers who participate in these studies. Lachenmeier’s team used volunteers to confirm the study samples that were positive for pine mouth. “This is a high burden for our taste panels,” he says.

It’s so sad that the delicious, delicious fatty little seeds could cause anyone anything but joy.

More reading on pine mouth:

“Link Between Nuts, ‘Pine Mouth Syndrome,’ Is Hard To Crack”

The Great Pine Nut Mystery blog

5 Comments

  • Jul 13th 201112:07
    by Rudy Baum

    Does everyone who ingests a bad pine nut develop pine mouth? Or is it possible that this is one of those phenomena like the aversion to cilantro that Alex Tullo wrote about in Newscripts (http://pubs.acs.org/isubscribe/journals/cen/88/i06/html/8806newscripts.html)?

  • Jul 13th 201112:07
    by Lauren Wolf

    Good question, Rudy. Because researchers don’t know what causes pine mouth yet, I’m not sure there’s a definitive answer. If the linalool oxide theory mentioned above is correct, though, I’d guess that everyone who has a bad pine nut would be affected. Cilantro aversion, on the other hand, seems to be genetic, based on Alex’s reporting. It will be interesting, however, to see what the culprit is when scientists eventually figure it out.

  • Jul 15th 201110:07
    by Lauren Wolf

    Not sure how I missed this, but it has been brought to my attention that there was another terrific blog post by scicurious last month on pine mouth. Check it out here: http://bit.ly/k4ZxMV

  • Jul 27th 201117:07
    by Dave

    I had this same problem but it ended up being from canned air dusters that you use on computers instead of pine nuts. Check out the site here Bitter Taste In Mouth . But the next time I ate pine nuts I noticed that they also cause it a little.

  • Mar 27th 201208:03
    by Max

    I think that I know that metallic taste exactly. I recently tried a bottle of alcohol-free Becks lager. At first I didn’t notice anything odd about the taste but within a few minutes there was a very strong metallic taste. It lasted for the best part of 2 days and even now I can vividly bring to mind the taste.

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