Abstract
To answer the question "How much caffeine do I have in my cup of tea?" we have developed a simple isocratic HPLC method with UV detection for determination of caffeine. The optimized method exhibits high repeatability; the retention time RSD was lower than 0.4% and RSD of the peak area was lower than 3.5%.
The method was applied to five types of tea in loose leaf form differing in level of fermentation (black, pu-erh, oolong, green, and white). The brewing conditions were chosen to be as close as possible to domestic preparation of tea.
In this study, we have focused on two important culinary factors: infusion time and brewing temperature. The results show that both investigated factors significantly influence the final content of caffeine in a cup of tea.
Increase in caffeine content was up to 29% when the tea infusion was overextracted by 1 min. Increase was even higher (up to 66%) when boiling water was used instead of water of recommended temperature.
It indicates that careful attitude to preparation of each type of tea is essential for caffeine content. [GRAPHICS] .