Thermal-induced changes of kale's antioxidant activity analyzed by HPLC-UV/Vis-online-TEAC detection

► Three kale cultivars were subjected to thermal treatment and investigated. ► During boiling, total phenolic content and total antioxidant activity remain unchanged. ► HPLC-online-TEAC revealed distinct changes in composition and activity of the flavonols. ► Degradation products compensate the loss of the antioxidant activity of the original compounds.