Recent interest into the possible benefits of l-theanine found in tea has raised the issue that there are few data available on amounts of l-theanine contained in cups of commercially-available teas, prepared by a standard method. HPLC along with a standard method of preparing tea was employed here to determine amounts of l-theanine in cups of tea and the effects that various preparation factors have on amounts of l-theanine extracted. Brewing time was found to be a major determinant of the amount of l-theanine extracted, while the addition of small amounts of milk and sugar made no significant difference. High levels of milk resulted in a marked lowering of the level of detectable l-theanine. Contrary to previous research, a standard (200. ml) cup of black tea was found to contain the most l-theanine (24.2 ± 5.7. mg) while a cup of green tea contained the least (7.9 ± 3.8. mg). © 2010 Elsevier Ltd.
Keenan, E. K., Finnie, M. D. A., Jones, P. S., Rogers, P. J., & Priestley, C. M. (2011). How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry, 125(2), 588–594. https://doi.org/10.1016/j.foodchem.2010.08.071