Integrated ozone micro-nano bubbles and slurry ice precooling enhance broccoli preservation during shelf-life storage

Conventional methods of precooling fresh vegetables are often limited by slow or uneven heat removal and excessive dehydration, which compromise their ability to maintain postharvest quality. Therefore, we developed an integrated precooling system combining ozone micro-nano bubble water with slurry ice (O₃-MNBSI precooling) and evaluated its effect on the overall postharvest quality preservation of broccoli and associated physiological parameters. Broccoli heads were precooled immediately after harvest in a slurry ice bath supplemented with 2.4 mg L^-1 ozone and subsequently placed under shelf-life (20 °C) conditions. Results indicated that O₃-MNBSI precooling substantially delayed floret yellowing and senescence under storage conditions. On day 4 of shelf-life storage, O₃-MNBSI-treated broccoli showed low weight loss, respiration rate, and ethylene production, with values of 0.64%, 1.42 mg CO₂ kg^-1 h^-1, and 0.0914 μL kg^-1 h^-1, respectively, while retaining 60.06% of the initial chlorophyll content. Concomitantly, antioxidant capacity was enhanced, as reflected by higher levels of peroxidase, catalase, and ascorbate peroxidase activity, as well as higher levels of vitamin C, total phenolics, and flavonoids. Combined transcriptomic and metabolomic analyses revealed that O₃-MNBSI precooling induced coordinated metabolic adjustments rather than alterations in random pathways. Phenylpropanoid biosynthesis was preferentially enhanced, which promoted the accumulation of antioxidant-related metabolites, while ethylene biosynthesis and hormone-associated signaling pathways were moderately impacted. Pigment metabolism was also stabilized through a balanced regulation of chlorophyll degradation and carotenoid metabolism, which resulted in a delay in visual deterioration. Overall, O₃-MNBSI precooling represents an effective and environmentally friendly strategy for maintaining the postharvest quality of broccoli.