Effects of various heating methods on glucosinolate, carotenoid and tocopherol concentrations in broccoli

The objective of this study was to determine the influence of heating (i.e. boiling, steaming and microwaving) on carotenoid, tocopherol and glucosinolate concentrations in broccoli. We detected five glucosinolate peaks in broccoli representing glucoraphanin, 4-hydroxyglucobrassin, glucobrassicin, 4-methoxyglucobrassicin and neoglucobrassicin. Various heating methods affected the concentrations of nutrients and health-promoting compounds in cruciferous vegetables. The concentrations of five glucosinolates in broccoli significantly decreased after different heating methods, and the rate of decrease was higher with increased cooking time. Cooking broccoli significantly increased the apparent concentrations of lutein, beta-carotene and alpha- and gamma-tocopherols. Our results clearly show that health-promoting compounds in broccoli are significantly affected by different heating methods and that all heating treatments reduced glucosinolate concentrations. However, carotenoid and tocopherol concentrations were increased by various heating methods, and a longer heating time increased their extractability.