Ultrahigh-Performance\nLiquid Chromatography-High-Resolution\nMass Spectrometry Analysis of Phytochemical Profiles of Kale (Brassica oleracea <i>var. sabellica</i>) Harvested at Different Stages of Development

Kale (Brassica oleracea <i>var. sabellica)</i> is a rich source of health-promoting\nphytochemicals.\nThe current study seeks to elucidate dynamic changes in phytochemical\nprofiles during kale maturation. Total and individual polyphenols\nand glucosinolates (GLs) from different developmental stages (microgreen,\nkale, mature, and postmature) of kale were determined and compared\nusing a high-resolution mass spectrometry (HRMS)-based metabolomics\nstrategy. A total of 51 polyphenols and 7 GLs were identified in the\nkale samples. In addition, we observed significant shifts in the metabolite\nprofiles of kale as the plant progressed from microgreens to mature\nleafy greens with distinct profiles at each growing stage. The total\npolyphenol levels were highest in the baby kales, while the GL levels\nwere highest in microgreens. Multivariate analysis identifies GLs\nand specific hydroxycinnamic acyl glycosides as prominent metabolites\nin microgreens; however, Quercetin (Qn)-glycosides and Qn-hydroxycinnamic\nacyl glycosides are unique metabolites in the baby kales. Our study\nprovides valuable insights into the changes in kale secondary metabolites\nthat occur during different stages of the vegetable’s production\ncycle.