Fracture and rheological properties of standardized, model solid foods influence their breakdown mechanisms during in vitro gastric digestion with simulated peristalsis

The physical breakdown of solid foods in the stomach is an important aspect of the overall digestion process. However, the mechanisms of breakdown of solid foods in the stomach are not fully understood. In this study, four standardized model solid foods with varying gastric softening kinetics were subjected to static in vitro digestion followed by digestion using either the Human Gastric Simulator (HGS), a physiologically representative model of gastric digestion, or using a peristaltic simulator to isolate the effect of peristalsis. Two of the model foods were based on the Standard American Diet with a strong and weak gel version, and the other two were simpler whey protein hydrogels, also with a strong and weak gel version. Physical properties of model foods such as toughness, yield stress, stiffness, and G’ (at 1 Hz) were significantly (p < 0.01) influenced by static in vitro digestion time and the type of model food. In the HGS, particles of model food with hardness < ca. 10 N broke down by erosion, chipping, and fragmentation whereas particles with hardness > ca. 40 N broke down only by erosion. Experiments in the peristaltic simulator showed that the model food with hardness ca. 20 N initially broke down by erosion and chipping but began to experience large-scale fragmentation after the application of ca. 30 peristaltic contractions had been applied, weakening the particle matrix. Overall, results from this study established the breakdown mechanisms for model foods with varying physical properties during in vitro digestion with simulated peristalsis.