Stem barks of cinnamon and roots of licorice were obtained from a local Chinese medicinal shop. Both were ground to fine powder. The powdered herbs (10g) were soaked in 100ml of distilled water and left overnight at 70˚C. The suspension was then centrifuged (2000 rpm; 15 min), and the supernatant was sterilized through 0.22 μm filter (Sartorius, Germany).