Kinetics of Gastric Juice Diffusion to Solid Food During Digestion

Knowledge about gastric juice migration into food during digestion is limited. During the food digestion process, as gastric juice penetrates into food, it creates a moving boundary, which differentiates the softer texture due to the action of the gastric juice from the initial texture of the food. The goal of this work was to study the kinetic of gastric juice diffusion and evaluate the location of the moving boundary by measuring texture and image analysis.;Potato samples cut in cylindrical shape were submerged in simulated gastric juice for 4 hr and the texture change in the samples was measured every 1 hr using a 2 mm flat-ended probe in a Texturometer (TA-XT2). Methylene blue dye was added into gastric juice to visualize its diffusion into the sample. A blue visible region showing gastric juice penetration profile was observed by taking images using a digital camera and the profile was analyzed for its intensity value using Image J software. Analytical solution of the Fick's diffusion equation was applied to predict the effective diffusivity of gastric juice into the food matrix. The viscosity of gastric juice was modified by adding guar gum (0.75% and 1.5% w/v) and the pH of gastric juice was varied from 1.8 to 3.0 and 5.3.;It was found that gastric juice diffusion into solid foods significantly depends on the pH of gastric juice, but not necessarily on the viscosity of gastric juice. Increasing pH of gastric juice from 1.8 to 3.0 and 5.3 delayed the advance of the moving boundary only. The effect of increasing guar gum concentration to 1.5% (w/v) on slowing down the gastric juice diffusion and decreasing the tender layer thickness in potato was seen only at pH 1.8 but not at pH 3.0 or 5.3, denoting that there was a minimum pH that altered the potato cellular structures and allowed the gastric juice to penetrate deeper into potato. It was determined that the internal resistance of the potato cellular structure remains the major rate limiting step of gastric juice diffusion into potato.