Onion slices were homogenised in a Waring blender and a 5 g sample was added to 40 ml of methanol-80. The content were mixed on a water-bath shaker for 1 h and centrifuged at 10,000xg for 10 min. Supernatant was collected and residues were re-extracted twice using 10 ml of methanol-80 by vortexing (1 min) and centrifugation at 10,000xg for 5 min. All three supernatants were combined for subsequent analyses.