Gastric pH Distribution and Mixing of Soft and Rigid Food Particles in the Stomach using a Dual-Marker Technique

Mixing of a particle-laden material during peristaltic flow in the stomach has not been quantified in vivo. Gastric mixing plays a key role in the digestion process; it determines the availability of acid and enzymes to individual food particles and controls the length of time particles will spend in the antral region, where they are subjected to mechanical breakdown from antral contraction waves. Solid particle mixing has been quantified using a dual-indigestible marker technique (TiO2 and Cr2O3) in soft (cooked brown and white rice) and rigid (raw and roasted almonds) particle meals fed to growing pigs. All meals consisted of two portions. Each portion was separately marked by one of the two indigestible markers, and the portions were sequentially fed to the pigs. At time periods ranging from 20 to 720 min after completion of the meal, ten intragastric chyme samples were taken from each pig to determine the marker concentration and pH value. Gastric pH was not homogeneous throughout the stomach and varied over time, with differences observed between soft and rigid meals (p<0.0001). The total percentage of each meal that was mixed was calculated using a statistically-based mixing index (M). White rice had the greatest amount of mixing, becoming 94 % mixed after 480 min of digestion compared to 72 % mixing for brown rice. Rigid particles underwent a slower mixing process and only arrived at 65 and 71 % mixing after 720 min for raw and roasted almonds, respectively. Meal composition plays a role in the overall meal mixing during gastric digestion.