According to an analysis published in the Journal of AOAC International, green tea supplements contained higher levels of compounds associated with a degradation of the catechins or flavonol glycosides in the tea leaves.
“Although there are some good green tea dietary supplement products, there is no way for the consumer to know the qualities of the green tea dietary supplement products from reading the labels,” report the researchers, led by Pei Chen, PhD a research chemist from the U.S. Department of Agriculture’s Agricultural Research Service (ARS).
In addition to the potential degradation compounds, the ARS scientists found that some products contained unlabeled ingredients, the intake levels varied significantly between products, as did the quality, and that solid green tea products were more chemically similar to tea leaves compared to liquid products.
“The claim that a green tea dietary supplement is a good alternative for tea leaves is questionable from a chemical composition point of view,” added Dr Chen and his co-workers.
Unacceptable lack of QC
Commenting on the results, Steven Dentali, PhD, chief science officer for the American Herbal Products Association (AHPA) told NutraIngredients-USA.com: “The finding of undeclared sucrose in one liquid sample, fenugreek extract in another, and an apparent lack of any green-tea components in a third indicates an unacceptable lack of adequate QC for those particular products.”
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, as well as aiding in weight management.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
The success has translated into a booming extract market, valued at a around $44m (€29.7m), according to recent report from Frost & Sullivan. The market is expected to grow by more than 13 per cent over the next seven years.
According to the new analysis, however, some green tea supplements may not offer the same chemical components as green tea beverages. Dr Chen and his co-workers analyzed 20 commercially available green tea dietary supplement products (12 tablets or capsules and 8 liquids) and eight green tea samples and compared the constituents using an analytical technique called HPLC/MS fingerprinting to evaluate the chemical composition of the samples.
The researchers do not name the products tested but do note that the dietary supplements represent “most of the big dietary supplement manufacturers […] purchased commercially”.
According to the data, there was a significant variation between the dietary supplements in solid form and the green tea leaves, with similarity scores ranging from 0.55 to 0.91. The variations were even more pronounced for liquid supplements, with similarity scores ranging from 0.12 to 0.89. These results, “suggest that the chemical variance across the green tea dietary supplement samples was significant”, said the researchers.
In addition to the wide variety regarding levels of green tea compounds, the researchers also detected the presence of various (un-labeled) ingredients, including sucrose and fenugreek.
“Our study,” wrote the ARS scientists, “demonstrated that degradation of flavonol glycosides or oxidation of catechin occurred during the manufacturing and storage processes for GTDS samples; some additives in the GTDSs were not labeled; the daily intake amount recommended by the labels varies significantly; the quality of GTDS varies significantly; and the solid GTDS products are more chemically similar to tea leaves compared to their liquid counterparts.
“The results demonstrate the urgency of QC for GTDS products,” they concluded.
Source: Journal of AOAC International
March 2011, Volume 94, Issue 2, Pages 487-497
“A Non-targeted Approach to Chemical Discrimination Between Green Tea Dietary Supplements and Green Tea Leaves by HPLC/MS”
Authors: J. Sun, P. Chen, L.-Z. Lin, J.M. Harnly