In this study, curly kale stored at 1 ◦
C for 3 and 6 weeks was compared with plants remaining in the
field regarding several properties related to human health and sensory quality. Cold storage had no effec
on the antioxidant capacity (ORAC assay), total phenols (Folin-Ciocalteu assay) or flavonol content, bu
reduced the content of vitamin C and soluble sugars. The ratio ascorbic:dehydroascorbic acid decreased
from about 3 to 0.5 upon storage. The largest changes in the content of bioactive compounds were found
in plants that remained in the field for 6 additional weeks, including many frost days. In these plants
the levels of flavonols, total phenols and antioxidant capacity were reduced by 25–35% and the vitamin
C content by more than 50%, whereas soluble sugars and dry matter increased by roughly 20% and 30%
respectively. Among all the curly kale samples, the antioxidant capacity was positively correlated with
the level of total phenols (r = 0.73, P < 0.001) and total flavonols (r = 0.70, P < 0.001). Values obtainedwith a
non-destructive method based on chlorophyll fluorescence (ChlF) were well correlated with the flavono
content in the leaves, with the highest correlation found for quercetin (r = 0.76, P < 0.001). Using the ChlF
method, the kinetics of the flavonol content during the experiment was recorded. The same method also
showed gradients of flavonol content within the plant, with the highest values in the upper leaves and in
the tip of the leaves. ChlF measurement, therefore, proved to be a quick and cost-effective alternative to
chemical analyses of the flavonol content in curly kale.