Abstract
Kale is a plant known and valued since antiquity as a healthy vegetable crop, used for culinary, decorative, but also healing purposes. The aim of the study was to examine the effect of harvest date on physiological status and nutritional composition of two kale cultivars: ‘Winterbor’ F<sub>1</sub> (blue-green leaves) and ‘Redbor’ F<sub>1</sub> (red-purple leaves). The leaves were harvested in three periods: before frost (&gt;0°C), after medium (−5.0°C) and heavy frost (−15.0°C). Content of dry weight, soluble sugars, l-ascorbic acid, carotenoids, chlorophylls, polyphenols, anthocyanins, as well as antioxidant activity and peroxidase activity were determined. Cold temperature significantly affected bioactive compounds of kale. The content of dry weight, soluble sugars, l-ascorbic acid, phenolics, and antioxidant activity increased after medium frosts for both cultivars. The level of anthocyanins also increased significantly for the ‘Redbor’ F<sub>1</sub> cultivar. After strong frost, most of the tested parameters (content of dry weight, soluble sugars, phenolics, anthocyanins, and total antioxidant and peroxidase activity) significantly increased. The chlorophyll <em>a</em> content was reduced by heavy frost in both seasons. Harvesting kale before and after frost may allow the level of biologically active ingredients to be regulated as cold also significantly affects the physiological status of the plants.
Highlights
Kale (Brassica oleracea L. var. acephala) is the one of the oldest forms of the Brassicaceae family, native to the eastern Mediterranean
Due to ever-lower temperatures, the kale cultivars showed an increase in dry weight content in their tissues and its level reached maximum after the occurrence of strong frost in both seasons (Tab. 1, Tab. 2)
Subzero temperature during the last two harvests had a significant influence on the biological value and physiological status of the tested kale cultivars ‘Winterbor’ F1 and ‘Redbor’ F1
Summary
Kale (Brassica oleracea L. var. acephala) is the one of the oldest forms of the Brassicaceae family, native to the eastern Mediterranean. Acephala) is the one of the oldest forms of the Brassicaceae family, native to the eastern Mediterranean. It is a plant with edible, strongly curled leaves of green to dark-red color. Leaves are characterized by the highest nutritional value among Brassica vegetables [1]. This crop is cultivated mainly for leaves, while the flowers, appearing in early spring, can enrich the diet, because they have high nutritional value [2,3]. Kale has the highest nutritional value according to the ANDI scale (aggregate nutrient density index) [7].
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