Rheological Characterization of Gastric Juices from Bread with Different Amylose/Amylopectin Ratios

Abstract

The purpose of this paper is to present a methodology for characterizing the rheological properties of heterogeneous gastric contents, for the first time, to our knowledge. Pigs were used as a model because their gastric system is similar to that of humans. Bread was chosen as a high-calorific, solid test meal. The bread was made with flours offering a wide range of amylose/amylopectin ratios. A specific method of extraction and measurement was developed. For the study, the vane test technique was chosen in order to take into account the heterogeneity and short lifetime of the boluses. The variation in viscosity values for each gastric system was compared with their moisture contents, different residence times in the stomach, and various amylose/amylopectin ratios. The viscosities decrease significantly as the residence time increases. Furthermore, we suggest that the amylose/ amylopectin ratio (Am/Ap) determines the moisture content, which then provides the viscosity level, since the gastric contents behave as a concentrated suspension. Pigs add variability to the results because the structure of the bolus depends on mastication.

Flow and mixing by small intestine villi

“…45 The digesta is described as an heterogeneous concentrated suspension. [1][2][3] During the process of digestion, this suspension is transformed and exhibits different rheological properties: Newtonian, shear-thinning, pseudo-plastic, yield stress, etc. The influence of these rheological properties on the mechanics of mixing and more generally on the fluid mechanics of the gastro-intestinal tract is an open question.…”

“…When γ ˙c tends to 0, the fluid behaviour is pseudo-plastic and representative of the rheological behaviour of the digesta in various compartments of the gut. [1][2][3] The mixing and absorption of nutrients of diffusivity D (in m 2 s −1 ) were modeled by the advection-diffusion equations…”

“…Thorough mixing of enzymatic secretions with the contents of the lumen is essential for their efficient interaction, generation and absorption of nutrients at the mucosal surface of the small intestine. The major constraints to such mixing are the high viscosity and the non-Newtonian characteristics of the gastro-intestinal content [1][2][3] and the low velocity of their flow at the boundaries of the lumen, which together result in very low Reynolds numbers. 4 It is most likely that flows and transfers in the lumen should limit biochemical reactions during food digestion.…”