OSLO (Reuters) - Herbal teas often contain unlisted extra ingredients such as weeds, ferns or bits of tree, according to a study by New York high school students that could help tighten labeling rules.
"A third of the herbal teas had things in them that are not on the label," Mark Stoeckle, of the Rockefeller University who helped oversee the project, told Reuters by telephone.
The students collected dozens of teas and herbal teas and found extra ingredients in some including ferns, grass, parsley, other weeds and even traces of an ornamental tree, Taiwanese cheesewood, they said.
"For me, the most surprising ingredient was the annual bluegrass," said Catherine Gamble, 18, of Trinity School. "It seems kind of outrageous to have it in a tea."
"I think nothing was outright poisonous...but things like camomile (found in some samples) have been known to cause allergic reactions to people. To have those in tea and unlabelled could be dangerous," she told Reuters.
The students said that three of 70 tea products tested and 21 of 60 herbal products contained rogue ingredients not on the labels.
The tea study, using $5,000 equipment for genetic testing and a technique known as DNA barcoding, could help regulators tighten labeling rules for teabags and make manufacturers improve what they put in the brews, they said.
Testing can be done for about $15 a sample and takes about 24 hours. The teas and infusions were from 33 manufacturers in 17 nations, according to the findings, published on Thursday in Nature's online journal Scientific Reports.
"It's a mystery why ingredients are unlisted," said Grace Young, 15. "It might just be a weed picked up during harvesting or the residue of a plant used in one product gets passed to the next product in a processing facility."
Stoeckle said extra ingredients such as camomile or parsley might be added deliberately to provide flavor or color. Or manufacturers may seek to sell full-looking tea bags and so pad them with filler.
"This is something that manufacturers and regulators could use," Stoeckle said of the DNA technique for tea. Importers, for instance, could double check if a shipment of dried leaves is really tea.
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Editing by Elizabeth Fullerton