Comparative evaluation of drying techniques on broccoli leaves: Microstructure, volatiles, active components and antioxidant traits

Broccoli generates large amounts of discarded stems and leaves after harvesting, if not properly utilized, lead to resource waste and environmental pollution. To optimize resource utilization, drying has become the preferred method for the high-value valorization of broccoli by-products. In this study, we investigated the effects of natural, hot air, microwave, heat pump-assisted, and freeze drying (ND, HAD, MD, HPD, and FD) on physical and chemical properties of broccoli leaves (BLs). Significant differences were observed in all aspects of BLs across different drying methods. Specifically, FD preserved microstructure integrity and yielded the highest brightness values, while FD and HPD treatments best retained the inherent green hue of BLs power. Both FD and HPD were rich in volatile organic compounds. Moreover, HPD contained the highest protein, total phenol, and flavonoid contents, along with the strongest antioxidant capacity. In summary, HPD is the most suitable method for drying BLs. To further validate its practical application, future studies could explore the optimization of heat pump drying parameters to balance drying efficiency and the retention of bioactive substances in broccoli leaves. Applying HPD-dried broccoli leaves as a functional ingredient in food formulations may provide a new avenue for the high-value utilization of broccoli by-products. • Addresses the critical issue of resource waste and environmental pollution from discarded broccoli stems and leaves, focusing on drying as a key strategy for their efficient utilization and preservation. • Systematically compares five drying methods (natural drying, hot air drying, microwave drying, heat pump-assisted drying, freeze drying) and evaluates their impacts on multiple quality attributes of broccoli leaves, including microstructure, color, VOCs, active ingredients, and antioxidant activity. • Identifies freeze drying (FD) as superior in preserving microstructure integrity and maintaining optimal color parameters ( L* and ΔE ). Highlights heat pump-assisted drying (HPD) as the most effective method, yielding the highest contents of protein, total phenols (TPC), and total flavonoids (TFC), along with the strongest antioxidant capacity (assessed via DPPH, ABTS, and FRAP assays). • Provides valuable insights for optimizing broccoli by-product processing, emphasizing HPD as the preferred approach to balance resource utilization and product quality.