Genotypic and climatic influence on the antioxidant activity of flavonoids in Kale (Brassica oleracea var. sabellica).

The influence of genotype and climatic factors, e.g. mean temperature and mean global radiation level, on the antioxidant activity of kale was investigated. Therefore, eight kale cultivars, hybrid and traditional, old cultivars, were grown in a field experiment and harvested at four different times. In addition to the investigation of the total phenolic content, the overall antioxidant activity was determined by TEAC assay and electron spin resonance spectrometry. A special aim was to characterize the contribution of single flavonoids to the overall antioxidant activity using an HPLC-online TEAC approach. The antioxidant activity and the total phenolic content were influenced by the genotype and the eco-physiological factors. The HPLC-online TEAC results showed that not all flavonol glycosides contribute to the overall antioxidant activity in the same manner. Taking the results of the structural analysis obtained by HPLC-ESI-MS(n) into account, distinct structure-antioxidant relationships have been observed.