Wheat-Germ-Derived Peptides Inhibit Enzymatic Browning via Copper Chelation and Multimode Tyrosinase Inhibition

Enzymatic browning contributes to substantial postharvest losses in fresh produce, creating demand for effective clean-label inhibitors. However, the antibrowning potential of food-derived bioactive peptides and their underlying mechanisms remain poorly understood. This study produced four defatted wheat germ protein hydrolysates (DWGPHs) using Pronase, Protease N, Protease P, and trypsin and evaluated their antibrowning activity. Pronase-DWGPHs exhibited the strongest tyrosinase inhibition (21.3 ± 3.2% at 2.5 mg/mL) and browning suppression in apple juice (66.4 ± 2.2% at 20 mg/mL). Eight peptides were identified, and three were further evaluated (LGQMPPQCR, SDSQVFLFANSK, and FGDHLVYYEK). Peptide LGQMPPQCR showed the highest activity, achieving 95.2 ± 3.7% tyrosinase inhibition and 81.1 ± 0.8% browning reduction in apple juice at 5 mg/mL (P < 0.05). Molecular docking indicated that inhibition involves active-site binding, substrate competition, and redox interactions. These findings demonstrate that DWGPHs are promising natural antibrowning agents and provide mechanistic insight to guide their future development.