Gastric clot formation and its role in modulating proteolysis of dietary fiber-fortified milk under simulated elderly gastrointestinal conditions

Optimizing nutritional strategies for the elderly requires a deep understanding of how food structure influences digestive behavior. This study explored the effects of dietary fiber fortification on milk digestion under simulated elderly gastrointestinal conditions (characterized by reduced gastric acidity, lower digestive enzyme activity, and slower motility), with a particular focus on the formation and properties of gastric clots and their impact on protein hydrolysis kinetics. Milk was fortified with polydextrose (PD), sodium alginate (SA), hydroxypropyl trimethyl ammonium chloride chitosan (HACC), or wheat bran (WB) at 10 mg/mL, and subjected to in vitro digestion modeling. The results demonstrated that dietary fibers significantly altered clot characteristics, such as mass, rigidity, and viscosity, thereby modulating enzymatic accessibility and digestion efficiency. HACC-Milk and WB-Milk formed larger, denser clots with increased mechanical strength and viscosity, resulting in reduced degrees of hydrolysis (26.15 ± 1.23% and 24.55 ± 1.05%, respectively) compared to control milk (30.31 ± 1.90%) by the end of intestinal digestion. In contrast, SA-Milk and PD-Milk generated softer, more fragmented clots, enhancing enzyme diffusion and yielding significantly higher hydrolysis levels (35.33 ± 1.43% and 32.60 ± 1.06%, respectively). Rheological and textural analyses confirmed that WB and HACC reinforced clot structure and hindered proteolysis, while SA and PD attenuated clot formation, promoting protein breakdown. These findings highlight the pivotal role of gastric clots in modulating protein digestion kinetics and provide insights for designing fiber-enriched dairy formulations tailored to the elderly.