Preparation of green tea extract
Fresh green tea leaves were collected from tea gardens of Mazandaran province. Then, were sorted, washed, and were dried under sunlight. The dried tea leaves were crushed in a blender and then sieved using 70/100 mesh sieve-set (Setyopratomo., 2014). The extraction carried out by mixing 1000 ml of 70% ethanol in distilled water to 100 g of green tea powder. The obtained mixture had agitated with a magnetic for 24 hours at 40 °C temperature. In the next stage, the extract separated by filtration. Then to obtain to a concentrate extract, the resultant liquid evaporated by oven at temperature 40 °C. Finally, the extract was converted to powder by employing a freeze dryer at -50°C and was kept in air-tight dark bottles in the freezer at -18°C until usage (Vuong et al., 2011). Nwuha et al. reported the green tea polyphenols solubility in ethanol solvent was five to seven times higher than in the water extracts (Nwuha et al., 1999).