Students’ barcode probe reveals unlisted ingredients
Take another look at that cup of tea. Three New York City high school students used DNA barcoding to discover that several herbal brews and a few brands of tea contain ingredients unlisted on the manufacturers’ package.
The teenagers also discovered genetic variation between broad-leaf teas exported from India versus small-leaf teas exported from China.
Guided by DNA barcoding experts at The Rockefeller University, an ethno-botanist at Tufts University and a molecular botany expert at The New York Botanical Garden, co-authors Catherine Gamble, 18, Rohan Kirpekar, 18, and Grace Young, 15, of Trinity School in Manhattan, published their findings in the Nature journal Scientific Reports.
The unlisted ingredients included weeds such as annual bluegrass and herbal plants such as chamomile. The surprise ingredients are mostly harmless but could affect a tiny minority of consumers with acute allergies. Three (4 percent) of the 70 tea products tested and 21 (35 percent) of 60 herbal products had unlisted ingredients.
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For example, an herbal infusion labelled “St. John’s wort” (Hypericum perforatum) included material from a fern in the genus Terpischore. A DNA barcode obtained from another herbal tea labelled “ginger root, linden, lemon peel, blackberry leaves, and lemongrass” matched annual bluegrass (Poa annua), a common weed unrelated to lemongrass. Four herbal infusions yielded sequences identical or nearly identical to the tea plant, C. sinensis but none listed “tea” as an ingredient. The most common non-label ingredient, found in seven herbal products, was chamomile (Matricaria recutita).
Four products yielded barcodes of plants closely matching parsley, but none listed ingredients in that plant family.
Other unlisted ingredients included the common weeds white goosefoot (Chenopodium album) and red bartsia (Odontites vernus); a garden flower, lantana (Lantana spp.); an ornamental tree, Taiwanese cheesewood (Pittosporum pentandrum); and herbal plants such as alfalfa (Medicago sativa), lemon balm (Melissa officinalis), heal-all (Prunella vulgaris), blackberry (Rubus spp.) and papaya (Carica papaya).
“After water, tea and its many herbal variations represent the world’s most popular beverage – by far. Literally billions of cups are consumed every day, more than all the coffee, pop and every other drink combined,” said Gamble. “What’s in those little bags of tea and herbal tea products is a matter of interest to billions of people.”
“It’s important to list every ingredient in a product because some people need to be very careful about what they consume,” said Kirpekar. “Allergy symptoms might be just watery eyes but some people can get more seriously sick and they’d never know the reason was in their comforting hot drink. We were surprised to find many herbal teas in particular with unlisted ingredients.”
“It’s a mystery why ingredients are unlisted,” added Young. “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. Maybe unlisted ingredients like chamomile or parsley are added to provide flavour or color to herbal teas, serving the same purpose as garlic or onion in cooking. Perhaps manufacturers want to sell full looking bags and pad them with filler.”
Teas are made from leaves of the tea plant, Camellia sinensis; herbal infusions, which are often called “teas,” use the roots, leaves, stems, seeds, or flowers of many different plants. But appearance does not easily identify the bits of dried plants, which sometimes are also cooked or fermented, that are used to prepare infusions and teas. The researchers found the plant DNA extremely resilient and obtained barcodes from 90 percent of the 146 products sampled
The products, half teas and half herbals, from 33 different manufacturers spanning 17 countries, were collected or purchased at 25 locations in New York City including stores, school dining halls, and the homes of the investigators.
Some of the DNA extractions and amplifications were carried out on a dining room table in the apartment of iBOL scientific advisor Mark Stoeckle with used lab equipment bought on the Internet for about $5,000. After extracting and amplifying the DNA in the home lab, the samples were mailed to a commercial DNA sequencing facility. The total cost of analysis was about $15 per sample and took about 24 hours.
“These results demonstrate a low-cost approach for plant identification that could be used in educational, regulatory, and research settings to produce practical information and scientific insight,” said Stoeckle.
In addition to the unlisted ingredients, the young scientists helped discover that the tea plant includes a genetic difference between broad-leaf assamica variety tea exported from India and small-leaf sinensis variety tea exported from China, the two largest tea-producing countries by far.