An amount of 100 g of uncooked or cooked frozen broccoli contain ingan approximately equal amount of stems and florets was blended with 100 ml of extraction solution (15 g meta-phosphoric acid:40 ml acetic acid:3.7 ml conc. sulfuric acid:450 ml water) for 30 s using a food chopper (Model 72705, Hamilton Beach Brands Inc., Southern Pines, NC, USA).