An in vitro study of theaflavins extracted from black tea to neutralize bovine rotavirus and bovine coronavirus infections

Crude theaflavin was extracted from black tea and then fractionated by HPLC into five components (initial peaks (IP), TF(1), TF(2A), TF(2B), and TF(3)). The crude extract and the various fractions of theaflavin were collected and tested, individually and in combination, for antirotaviral activity. The mean effective concentration (EC(50)) was calculated and compared. Activity varied from the most active being the uncharacterized theaflavin-like initial peaks (IP) with an EC(50) of 0.125 μg/ml to the least active being theaflavin-3 monogallate (TF(2A)) with an EC(50) of 251.39 μg/ml. The combination of TF(1)+TF(2A)+TF(2B)+TF(3) was more active than the sum of the activities of these four fractions individually, indicating synergism among the peaks. Only the crude extract was assayed for activity against coronavirus; the EC(50) was 34.7 μg/ml.