Carotenoid composition of kale as influenced by maturity, season and minimal processing

The principal carotenoids of kale were identified by chemical reactions, high‐performance liquid chromatography/mass spectrometry and high‐performance liquid chromatography/photodiode array detection and were quantified by the last technique. In kale taken from conventional farms, the β‐carotene and lutein contents were significantly higher in the mature leaves, violaxanthin was at an unusually high level in the young leaves, and neoxanthin had practically the same concentration at both stages of maturity. In samples taken from an organic farm, the carotenoid contents were essentially the same in the young and the mature leaves. Except for β‐carotene, which did not differ with season, the carotenoid concentrations of marketed minimally processed kale were found to be significantly higher in the summer than in the winter, reflecting seasonal rather than processing effects. In minimally processed kale monitored during 5 days of storage at 7–9 °C, β‐carotene, lutein, violaxanthin and neoxanthin were reduced by 14, 27, 20 and 31% respectively. Thus minimal processing, seasonal and maturity factors were found to have an influence on the carotenoid content of kale.