Effect of succinic anhydride-derived succinylation on structural functional characteristics, amino acid profiling, biological activity, and digestibility of pumpkin peel protein.

In the present study, native pumpkin peel protein (PPP) was extracted using alkaline solubilization followed by isoelectric precipitation, yielding 61.3% protein. To enhance its functionality, PPP was chemically modified via succinylation using a 4:1 M ratio of succinic anhydride to lysine residues under controlled alkaline conditions. Structural modifications in succinylated pumpkin protein (MPPP) were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and particle-size and zeta-potential analyses. Functional properties, including solubility, water- and oil-holding capacities, emulsifying behavior, and foaming characteristics, were evaluated, along with antioxidant activity and in vitro digestibility. Succinylation significantly improved protein functionality, with increased solubility (65.66%), water-holding capacity (5.04 g/100 g), oil-holding capacity (2.54 g/100 g), and emulsifying capacity (34.10%). The zeta potential shifted from -5.5 mV to -24.1 mV, indicating enhanced electrostatic stability, accompanied by a reduction in particle size. FTIR confirmed the incorporation of succinyl groups, while SEM and XRD revealed structural loosening and increased amorphous character. Amino acid profiling showed a marked reduction in lysine content, confirming targeted modification. Improved antioxidant activity and enhanced in vitro digestibility further demonstrated the biological relevance of the modified protein. Importantly, this study establishes a matrix-specific mechanism in which succinylation disrupts protein-polysaccharide-phenolic interactions unique to pumpkin peel, leading to enhanced functional performance. These findings highlight the potential of succinylation as an effective strategy for valorizing pumpkin peel into a functional ingredient suitable for applications in food and nutraceutical systems.