Species-Specific Antioxidant and Metabolic Responses to Selenium in Brassica Microgreens

Selenium (Se) biofortification is a promising approach to improve the nutritional value and functional quality of microgreens, although species-specific responses to Se remain insufficiently understood. This study investigated the effects of Se biofortification on physiological status, antioxidant responses, phenolic composition, and molecular changes in four Brassica microgreens: broccoli, kohlrabi, pak choi, and kale, using biochemical analyses, HPLC, and FTIR spectroscopy. The indicators of nutritional quality and stress-related metabolism in Brassica microgreens showed species-specific responses due to selenium treatment. Kohlrabi showed coordinated osmotic and metabolic adjustment involving osmolyte accumulation and enhanced antioxidant response, although moderate membrane sensitivity was observed at the highest selenium concentration. Pak choi maintained tolerance through balanced metabolic adjustment and enzymatic defense, while broccoli responded predominantly through enzymatic antioxidant mechanisms. Kale exhibited pronounced non-enzymatic responses, including anthocyanin accumulation and enhanced radical scavenging capacity. PCA confirmed species-specific response strategies and differential associations among biochemical parameters. Changes in antioxidant functionality were associated with both metabolite accumulation and structural reorganization of phenolic-related compounds. Overall, Se biofortification improved functional and nutritional traits of the investigated Brassica microgreens, although higher selenium concentrations induced moderate oxidative and membrane-related stress in certain Brassica microgreens. These findings highlight the importance of species-specific optimization of Se application to maximize crop quality while minimizing potential effects of Se toxicity.