Hydrogen sulfide modulation of quality traits and antioxidants in broccoli sprouts

Broccoli sprouts are valued for their rich nutritional profile. Hydrogen sulfide (H 2 S) is a rapid plant signal that can enhance the nutritional and functional quality of sprouts. In this study, a single 1.0 mM NaHS spray followed by short-term sampling (0, 3, 9, and 24 h) revealed fast and coordinated responses in broccoli sprouts. Primary quality traits, including vitamin C, soluble sugars, soluble proteins, and total phenolic, increased and generally peaked at 24 h. Antioxidant capacity was strengthened through higher SOD, POD, CAT, and the AsA-GSH cycle enzymes, with enhanced ·OH scavenging and unchanged MDA despite modest late increases in ROS. The shikimate-phenylpropanoid network was activated, leading to selective enrichment of phenolic acids and individual flavonoids such as kaempferol. Free amino acids broadly accumulated, with pronounced increases in sulfur-containing and branched-chain amino acids (e.g., Met, Cys, Val, Arg). The glucosinolate-myrosinase-isothiocyanate axis was also strengthened. Total glucosinolates and isothiocyanates increased together with myrosinase activity. Collectively, exogenous H 2 S acts within hours as a redox cue to reinforce antioxidant defenses and redirect carbon-nitrogen-sulfur fluxes, co-optimizing nutritional quality and bioactive metabolite output. The most responsive window was 9-24 h post-treatment, suggesting a feasible preharvest strategy to elevate microgreen health value.