2.3. Preparation of tea extract
Green tea, oolong tea and black tea were purchased in
bulk. Tea leaves were grounded in a miller as temperature of
the container was maintained at less than 50°C. Tea powder
was extracted with 95% ethanol (1:10, w/v) for 2 h with
constant stir. Suspension was filtered through Whatman No.
1 filter paper to retain the clear solution. The residue was
extracted again. The pooled tea solution was vacuum evap-
orated below 50°C. The dried extracts were stored at 4°C.