Comparison of methods for postprandial intragastric pH measurement in a pig model during digestion of plant-based foods with different structures

IntroductionLuminal pH is a key determinant of food disintegration in the stomach, acting both on their biochemicalstructures and on the activity of digestive enzymes.ObjectiveThe present study aimed at monitoring postprandial intragastric pH variation after ingestion of fourplant-based meals having the same macronutrients content: two liquids (soymilk and a pea emulsion)and two solids (seitan and tofu).MethodologyFour mini-pigs fitted with a gastric cannula located on the stomach greater curve were used. Threerecording methods were compared: chyme sampling from cannula, a classic pH meter-catheterequipped with two probes or a wireless pH sensor directly put inside the stomach through the canula.Gastric emptying was also investigated using indigestible markers sampled from duodenal cannulaon six other mini-pigs. In vitro multi-scale characterization in gastric condition were assessed inin vitro conditions in order to explain intragastric pH differences observed in vivo.Main findingsDistribution of variation coefficients allowed us to detect the method inducing the less interindividualvariability. The average values obtained from the catheter system and the wireless sensor wereconsistent with each other, while sampling method gave less meaningful results. Food effect washighlighted: an exponential decrease occurred with solids while liquids observed a plateau at pH 7that lasted about 2h before a sigmoid-type decrease. The seitan appeared to empty faster from thestomach than the other foods, that could explain the quick pH decrease observed in the stomach. Itwas not the case for tofu explained probably by aggregation, buffering capacity or nitrogen solubility.Finally, entire gastric pH curves were modeled for each meal, that will be useful for implementing invitro dynamic digestion in relevant conditions.ConclusionIn conclusion, pH recording with catheter remained better than other methods and food macrostructureappeared to impact significantly gastric pH.