DNA testing by high school students shows many teas contain unlisted ingredients

Your tea may not be what you think. Three New York City high school students, working with Rockefeller scientists, have found several herbal brews and a few brands of tea contain ingredients unlisted on the manufacturers’ package. The teen sleuths also demonstrated new-to-science genetic variation between broad-leaf teas from exported from India versus small-leaf teas exported from China.

The team, including DNA “barcoding” experts at The Rockefeller University, an ethno-botanist at Tufts University and a molecular botany expert at The New York Botanical Garden, as well as co-authors Catherine Gamble, 18, Rohan Kirpekar, 18, and Grace Young, 15, of Trinity School in Manhattan, published their findings today in the Nature journal Scientific Reports.

Tea check. Grace Young (left), Catherine Gamble and Rohan Kirpekar examine tea packaging at a New York area supermarket.

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. Four percent of the 70 tea products tested and 35 percent of 60 herbal products had unlisted ingredients.

For example, DNA testing showed that an herbal infusion labelled “St. John’s wort” (Hypericum perforatum) included material from a fern in 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.

“After water, tea and its many herbal variations represent the world’s most popular beverage by far,” says Gamble. “Literally billions of cups are consumed every day, more than all the coffee, pop and every other drink combined. What’s in those little bags of tea and herbal tea products is a matter of interest to billions of people.”

DNA barcoding technology identifies and distinguishes known and unknown species quickly, cheaply, easily and accurately based on a snippet of genetic code. Experts at various institutions around the world are building an authoritative library of DNA barcodes for both plants and animals.

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 mentor and barcoding expert Mark Stoeckle, an adjunct faculty member with the Program for the Human Environment at The Rockefeller University. The lab equipment was purchased used on the Internet for about $5,000, highlighting the viability of public DNA-based plant identification. After extracting and amplifying the DNA in the home lab, the samples were mailed to a commercial DNA sequencing facility. The total cost was about $15 per sample and took about 24 hours in total.

Most of the DNA analysis was done at The New York Botanical Garden. When the students obtained a DNA sequence, they checked it using the GenBank DNA database maintained by the US National Library of Medicine, which retrieves matching sequences and candidate species names almost instantly.

“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,” says Stoeckle.

For more information, visit the TeaBOL Web page.

Scientific Reports online: July 21, 2011 Commercial teas highlight plant DNA barcode identification successes and obstacles Mark Y. Stoeckle, Catherine C. Gamble, Rohan Kirpekar, Grace Young, Selena Ahmed and Damon P. Little