Valorization of Desalted Duck Egg White through Enzymatic Hydrolysis: Gastric Digestion Behavior and Antioxidant Responses

This study investigated the gastric-phase digestion behavior and antioxidant responses of enzymatic protein hydrolysates produced from desalted duck egg white (DS-DEW) and evaluated their potential for value-added food ingredient development. Duck egg white proteins were subjected to enzymatic hydrolysis, and a modified INFOGEST static in vitro digestion model focusing exclusively on the gastric phase was applied to native duck egg white (DEW), desalted duck egg white (DS-DEW), duck egg white hydrolysate (DEWH), desalted duck egg white hydrolysate (DS-DEWH), and commercial egg white powder (EWP). Proteolysis during digestion was assessed by acid consumption kinetics, while free amino acid (FAA) release and antioxidant responses were evaluated using HPLC, DPPH radical-scavenging, and ferric-reducing antioxidant power (FRAP) assays. Native and non-hydrolyzed samples (DEW, DS-DEW, and EWP) exhibited high acid uptake during gastric digestion (90%-95%), whereas pre-hydrolyzed samples (DEWH and DS-DEWH) showed markedly lower acid consumption (< 20%), reflecting extensive peptide bond cleavage prior to gastric digestion rather than reduced digestibility. DS-DEWH exhibited the highest absolute FAA content after digestion (303.25 ± 4.38 mg/g), approximately 22-fold higher than EWP, indicating greater availability of hydrolysis products under acidic, pepsin-driven conditions. Antioxidant evaluation using chemical assays showed that DS-DEWH displayed significantly higher DPPH radical-scavenging activity (42.67%) and FRAP values (3.71 ± 0.69 µmol TE/g) than DEW and DS-DEW (p < 0.05). Due to analytical constraints, EWP was excluded from antioxidant assays. Overall, enzymatic hydrolysis altered gastric-phase digestion behavior and enhanced free amino acid availability and antioxidant responses of desalted duck egg white at the chemical-assay level, supporting its valorization as a sustainable food protein ingredient.