The effect of pressure on the extraction yields of caffeine. HPP extraction: 50% ethanol, pressure application for 5 min, liquid/solid ratio – 20:1 (mL/g); 5 g dry green tea leaf powder. The control HPP extraction: 50% ethanol concentration, 0.1 MPa pressure for 5 min, liquid/solid ratio – 20:1 (mL/g), 5 g dry green tea leaf powder. Bars are means ± standard deviations of triplicate measurement (P < 0.05, Student’s t-test).