The kinetic of key phytochemical compounds of non-heading and heading leafy Brassica oleracea landraces as affected by traditional cooking methods

BACKGROUND: Kales are often a key ingredient of traditional foods, containing high amounts of indolic glucosinolates (precursors of indole-3-carbinol and ascorbigen), carotenoids and phenolics. The present trend to associate traditional foods crops with health-promoting properties suggested to investigate the degradation kinetic of three Brassica oleracea landraces' phytochemicals subjected to boiling, steaming and stir-frying. RESULTS: Boiling led to substantial losses due to leaching. Glucosinolates followed a second-order degradation kinetic (20% of their initial values after 10 min in Nero di Toscana). Phenolic content in leaves + cooking water remained unchanged, whereas their antioxidant capacity was reduced. Carotenoid content increased during the first minutes of boiling. Steaming showed the highest retention of phytochemicals, with often zero-order degradation kinetic, having however a strong effect on colour. Stir-frying produced high losses for all measured compounds; also, β-carotene reduced its content to 10–23% independently of variety. Conversion values for indole-derived compounds ranged from non-detectable to 23.5%. CONCLUSION: Variety strongly affected observed degradation rates because of a different glucosinolate composition and leaf structure. With this research, more information has been gained on the degradation kinetic of B. oleracea landraces' phytochemical compounds upon cooking, highlighting the possibility of improving bioactive component retention. © 2016 Society of Chemical Industry.