The stem and bark of ripe pineapple fruit were separated from the fleshy fruit. The stem and bark portions were then cut into small pieces and crushed in an industrial blender (Siemsen TA- 04, Brazil) with deionised water (1:1 w/w) to get approximately 500 ml of juice, which was filtered through a Vual tissue to remove the fibrous material. The filtered juice was centrifuged (Jouan BR4i, France) at 15,000g for 15 min at 4 °C to remove insoluble materials. The clear supernatant obtained, called crude extract, was stored in aliquots (2 mL) at 18 °C, and used whenever required.