A Cold Case—Glucosinolate Levels in Kale Cultivars Are Differently Influenced by Cold Temperatures

Abstract

Among the Brassica oleracea L. crops, kale has gained increased global recognition in recent years as a healthy food item due to its high nutritional value and versatility. Additionally, the diversity of different kale varieties has started to be explored across large latitudes from the Mediterranean to north temperate climates. Specifically, glucosinolates are the predominant phytochemicals found in kale leaves, contributing to the specific taste of this vegetable, and they are affected by environmental factors such as temperature. To date, no study has investigated the effect of chilling on glucosinolate diversity and, thus, the taste in genetically different kale cultivars at the same time. Given the variability of glucosinolates observed among cultivars, we evaluated the impact of acclimation to cold temperatures on glucosinolate levels in curly kale, Lacinato kale, and a feral type using high-performance liquid chromatography coupled with time-of-flight mass spectrometry (HPLC-ESI-qTOF-MS). We targeted the short-term impact (after 12 h) on glucosinolates as well as the longer-term effect (after seven days) of cold acclimation. Our results revealed different molecular patterns regarding the change in glucosinolates in the feral type compared to curly kale and Lacinato-type kale. In the latter ones, primary aliphatic glucosinolates were induced (the glucoraphanin in Lacinato kale increased by more than 200%). The indole glucobrassicin was not significantly affected. Conversely, in the feral type the indole glucobrassicin was reduced by 35% after cold acclimation, whereas aliphatic glucosinolates were hardly affected. The results indicate that both genetic and environmental factors are important for the composition of glucosinolate patterns in kale. In conclusion, to obtain plants with an improved nutritional value, considering both temperature and the choice of cultivar is crucial during kale cultivation. Future breeding attempts of kale should also emphasize the cultivar-dependent cold acclimation patterns reported here.