Differences in Leaf Color and Stage of Development at Harvest Influenced Phytochemical Content in Three Cultivars of Kale (Brassica oleracea L. and B. napus)

Microgreens and red colored plants have been suggested to contain higher level of health promoting phytochemicals. Kale (Brassica oleracea L. and other species) is regarded as a 'superfood' due to its antioxidant properties. In our study, three kale cultivars (B. oleracea L. 'Dwarf Blue Curled' and 'Scarlet', and B. napus 'Red Russian') differing in leaf pigmentation were harvested at five different leaf developmental stages and the concentrations of bioactive antioxidants compounds were evaluated. Carotenoids were measured by high performance liquid chromatography, and spectrometry analyses were used for total phenolics and anthocyanin measurements. Red leaf kale ('Scarlet') was generally higher in total carotenoids, phenolics, and anthocyanins than green leaf kales ('Dwarf Blue Curled' and 'Red Russian'). As kale matured, water content decreased and dry mass increased. On a dry weight basis, total carotenoids were more abundant in microgreens and young seedlings with 4 to 6 true leaves (baby greens) than adult stage. In contrast, on a fresh weight basis, baby greens or adult kales generally contained more carotenoids and total phenolic compounds than microgreens, more likely due to the lower dry mass and phytochemical accumulation at microgreen stages. Although some microgreens vegetables may contain more health promoting phytochemicals, based on our study, higher phytochemicals were detected in young seedlings or mature leaves of kale.