Ultrahigh-Performance Liquid Chromatography-High-Resolution Mass Spectrometry Analysis of Phytochemical Profiles of Kale (Brassica oleracea var. sabellica) Harvested at Different Stages of Development

Kale (Brassica oleraceavar. sabellica) is a rich source of health-promoting phytochemicals. The current study seeks to elucidate dynamic changes in phytochemical profiles during kale maturation. Total and individual polyphenols and glucosinolates (GLs) from different developmental stages (microgreen, kale, mature, and postmature) of kale were determined and compared using a high-resolution mass spectrometry (HRMS)-based metabolomics strategy. A total of 51 polyphenols and 7 GLs were identified in the kale samples. In addition, we observed significant shifts in the metabolite profiles of kale as the plant progressed from microgreens to mature leafy greens with distinct profiles at each growing stage. The total polyphenol levels were highest in the baby kales, while the GL levels were highest in microgreens. Multivariate analysis identifies GLs and specific hydroxycinnamic acyl glycosides as prominent metabolites in microgreens; however, Quercetin (Qn)-glycosides and Qn-hydroxycinnamic acyl glycosides are unique metabolites in the baby kales. Our study provides valuable insights into the changes in kale secondary metabolites that occur during different stages of the vegetable's production cycle.