Age-specific gastrointestinal conditions alter the structural dynamics and digestive fate of walnut protein during in vitro digestion

Using the INFOGEST in vitro model, this study investigated how age-specific gastrointestinal conditions (toddler, adult, elderly) modulate the structural changes of walnut protein (WP) and how these changes influence the digestive fate. Results showed that digestion transformed WP from compact to loose structures, with adults exhibiting the most pronounced alterations due to higher enzyme activity and bile salts concentration. Notably, while adults showed the highest gastric digestibility, net intestinal digestibility was higher in the elderly (47.3%) and toddlers (40.6%) than in adults (32.1%), which may reflect compensatory intestinal digestibility when gastric digestion was limited. This compensation may be driven by age-dependent structural dynamics: adults formed large aggregates during gastric digestion due to reduced electrostatic repulsion and increased viscosity. Conversely, toddlers and elderly maintained smaller particles and lower viscosity, facilitating more efficient intestinal digestibility. Peptidomic analysis revealed that these differential pathways generated age-specific peptide profiles. In adults, the higher degree of hydrolysis (DH) resulted in a greater proportion of peptides below 3 kDa, which were predicted to possess enhanced bioactivity. Toddlers and the elderly retained distinct peptide sequences and were predicted to contain more peptides with potential DPP-IV and ACE inhibitory activities. These findings demonstrate that age-related gastrointestinal conditions alter WP digestion through structural modification mechanisms, providing a basis for developing age-tailored protein products.