Leaf Developmental Stage at Harvest Affects Postharvest Senescence and Quality Parameters of Kale

Background: Kale is a vegetable of the Brassicaceae family recognized for its high nutritional value. After harvest, kale leaves undergo senescence, characterized by the loss of green color due to chlorophyll degradation. This deterioration affects organoleptic quality and consumer acceptance. Objective: The present study investigated the effect of leaf developmental stage at the moment of harvest on postharvest senescence and parameters related to the nutritional quality of kale during postharvest storage at 20 °C. Material and Methods: Kale leaves were harvested at three developmental stages—young inner leaves (~20 cm), middle leaves (central position, 20–30 cm), and mature outer leaves (35–40 cm)—and stored at 20 °C for six days in darkness with an RH of 90–95%. At harvest and after two, four, and six days of storage, superficial color, weight loss, total phenolic and flavonoid contents, antioxidant capacity, total and reducing sugars, and total and soluble proteins were evaluated. Because yellowing is the main postharvest symptom in kale leaves, the relative expressions of chlorophyll catabolic genes such as NYC, NOL, SGR, PPH and PaO were also analyzed. Results: The leaf development stage strongly influenced postharvest life and the biochemical composition of the leaves. Inner leaves showed a lower rate of chlorophyll degradation during postharvest storage and retained a more intense green color, consistent with a reduced expression of chlorophyll catabolic genes. In contrast, middle and outer leaves exhibited greater chlorophyll loss and more pronounced yellowing. Inner leaves maintained the best overall visual quality at the end of storage and showed higher phenolic as well as greater antioxidant capacity compared with middle and outer leaves. Inner leaves also contained higher levels of reducing sugars and soluble proteins. Conclusions: Taken together, these findings indicate that harvesting kale at earlier developmental stages might represent an effective strategy to extend shelf-life and provide a product with improved values in the parameters actually measured.