Egg white gel structure determines biochemical digestion with consequences on softening and mechanical disintegration during in vitro gastric digestion.

The aim of this work was to investigate the role of biochemical digestion on softening and disintegration kinetics of pH 5 and pH 9 egg white gel (EWGs) during in vitro gastric digestion. EWG samples (5 mm length cubes) underwent in vitro digestion by incubation in simulated gastric fluid at different time intervals for up to 240 min. The hardness was measured using a Texture Analyser; softening kinetics was fit to the Weibull model. Results revealed that pH 9 EWG had the highest softening halftime (458 ± 86 min), indicating the slowest softening, whereas pH 5 EWG had the lowest softening halftime (197 ± 12 min), indicating the quickest softening. The digested samples were immediately exposed to mechanical forces generated by the human gastric simulator (HGS) for 10 min to investigate the influence of gastric juice on the breakdown behaviour of EWG cubes. The breakdown behaviour of the disintegrated samples was characterized by fitting the cumulative distributions of particle surface areas to a mixed Weibull function (R2 > 0.99). The weight of fine particles (α) showed that regardless of gastric juice diffusion, the pH 5 EWG (α = 0.22 ± 0.03) disintegrated into more fine particles than those resulting from pH 9 EWG disintegration (α = 0.07 ± 0.02). As expected, the diffusion of gastric juice enhanced erosion of the EWG particles into fine particles. Result obtained from the particle surface area distribution is in good agreement with the softening kinetics of EWGs during simulated in vitro gastric phase.

Role of biochemical and mechanical disintegration on ß-carotene release from steamed and fried sweet potatoes during in vitro gastric digestion.

The role of biochemical and mechanical disintegration on ß-carotene release from steamed sweet potatoes (SSP) and fried sweet potatoes (FSP) during in vitro gastric digestion was investigated. Results revealed that, in the absence of mechanical forces generated by the stomach, biochemical digestion did not have a great effect on the breakdown of cell walls within the sweet potato food matrix and the release of ß-carotene was similar in both SSP and FSP. Cell wall in the plant-food may act as a physical 'barrier' towards the action of gastric juice and to the release of nutrients into the gastric digesta. However, FSP underwent quicker softening and collapse during in vitro gastric digestion compared to the compact and denser structure of SSP. This may explain the faster cell wall breakdown and subsequent ß-carotene release from FSP cellular matrix than SSP when mechanical forces are applied as in the human gastric simulator (HGS).

Food material properties as determining factors in nutrient release during human gastric digestion: a review.

The fundamental mechanisms of nutrient release from solid foods during gastric digestion consists of multiple elementary processes. These include the diffusion of gastric juice into the food matrix and its simultaneous enzymatic degradation and mechanical breakdown by the peristaltic activity of the stomach. Understanding the relative role of these key processes, in association with the composition and structure of foods, is of paramount importance for the design and manufacture of novel foods possessing specific target behavior within the body. This review covers the past and current literature with respect to the in-stomach processes leading to physical and biochemical disintegration of solid foods and release of nutrients. The review outlines recent progress in experimental and modeling methods used for studying food disintegration mechanisms and concludes with a discussion on potential future research directions in this field. Information from pharmaceutical science-based modeling approaches describing nutrient release kinetics as a result of food disintegration in the gastric environment is also reviewed. Future research aimed at understanding gastric digestion is important not only for setting design principles for novel food design but also for understanding mechanisms underpinning dietary guidelines to consume wholesome foods.

Mapping the Spatiotemporal Distribution of Acid and Moisture in Food Structures during Gastric Juice Diffusion Using Hyperspectral Imaging.

This study investigated the feasibility of using hyperspectral imaging (HSI) to characterize the diffusion of acid and water within food structures during gastric digestion. Two different sweet potatoes (steamed and fried) and egg white gel (pH5 and pH9 EWGs) structures were exposed to in vitro gastric digestion before scanning by HSI. Afterward, the moisture or acid present in the digested sample was analyzed for calibration purposes. Calibration models were subsequently built using partial least-squares (PLS). The PLS models indicated that the full-wavelength spectral range (550-1700 nm) had a good ability to predict the spatial distribution of acid (Rcal2 > 0.82) and moisture (Rcal2 > 0.88). The spatiotemporal distributions of moisture and acid were mapped across the digested food, and they were shown to depend on the food composition and structure. The kinetic data revealed that the acid and moisture uptakes are governed by Fickian diffusion or by both diffusion and erosion-controlled mechanisms.

Spatial-temporal changes in pH, structure and rheology of the gastric chyme in pigs as influenced by egg white gel properties.

The hypothesis is that the characteristics of ingested protein gels influences the subsequent in vivo gastric digestion process. Three egg white gels (EWGs) of identical composition but differing in structure and texture were prepared and fed to pigs. Sampling throughout a 6 h postprandial period, and at different locations in the stomach of the pigs, enabled a detailed spatial-temporal mapping of the pH, dry matter content, particle size and rheological properties. The results showed different gastric acidification kinetics implying an effect of the gel structure and/or texture. The most elastic and cohesive gel resulted in the highest median particle size and the most viscoelastic chyme. Distal and proximal regions of the stomach did not differ in terms of dry matter content, particle size distribution or rheological properties. These results demonstrate the consequences of protein food structure on gastric chyme properties, and thus suggest an effect on the digestion process.

A proposed food breakdown classification system to predict food behavior during gastric digestion.

The pharmaceutical industry has implemented the Biopharmaceutics Classification System (BCS), which is used to classify drug products based on their solubility and intestinal permeability. The BCS can help predict drug behavior in vivo, the rate-limiting mechanism of absorption, and the likelihood of an in vitro-in vivo correlation. Based on this analysis, we have proposed a Food Breakdown Classification System (FBCS) framework that can be used to classify solid foods according to their initial hardness and their rate of softening during physiological gastric conditions. The proposed FBCS will allow for prediction of food behavior during gastric digestion. The applicability of the FBCS framework in differentiating between dissimilar solid foods was demonstrated using four example foods: raw carrot, boiled potato, white rice, and brown rice. The initial hardness and rate of softening parameter (softening half time) were determined for these foods as well as their hypothesized FBCS class. In addition, we have provided future suggestions as to the methodological and analytical challenges that need to be overcome prior to widespread use and adoption of this classification system. The FBCS gives a framework that may be used to classify food products based on their material properties and their behavior during in vitro gastric digestion, and may also be used to predict in vivo food behavior. As consumer demand increases for functional and "pharma" food products, the food industry will need widespread testing of food products for their structural and functional performance during digestion.

On the kinematics and efficiency of advective mixing during gastric digestion - A numerical analysis.

The mixing performance of gastric contents during digestion is expected to have a major role on the rate and final bioavailability of nutrients within the body. The aim of this study was to characterize the ability of the human stomach to advect gastric contents with different rheological properties. The flow behavior of two Newtonian fluids (10(-3)Pas, 1Pas) and a pseudoplastic solution (K=0.223Pas(0.59)) during gastric digestion were numerically characterized within a simplified 3D model of the stomach geometry and motility during the process (ANSYS-FLUENT). The advective performances of each of these gastric flows were determined by analyzing the spatial distribution and temporal history of their stretching abilities (Lagrangian analysis). Results illustrate the limited influence that large retropulsive and vortex structures have on the overall dynamics of gastric flows. Even within the distal region, more than 50% of the flow experienced velocity and shear values lower than 10% of their respective maximums. While chaotic, gastric advection was always relatively poor (with Lyapunov exponents an order of magnitude lower than those of a laminar stirred tank). Contrary to expectations, gastric rheology had only a minor role on the advective properties of the flow (particularly within the distal region). As viscosity increased above 1St, the role of fluid viscosity became largely negligible. By characterizing the fluid dynamic and mixing conditions that develop during digestion, this work will inform the design of novel in vitro systems of enhanced biomechanical performance and facilitate a more accurate diagnosis of gastric digestion processes.

Propagating longitudinal contractions in the ileum of the rabbit--efficiency of advective mixing.

Three longitudinal motions of the rabbit small intestine were modelled in the CFD software Polyflow using ex vivo experimental data previously reported in literature. Consideration was given to chyme rheology and mixing performance of the macro-scale lumenal motions, as triggered by the observed wall motions. Simulations were performed to qualitatively assess the flow behaviour. The advective properties of the flow were universally characterised by analysing the stretching ability of the flow. Two Newtonian fluids, with viscosities of µ = 1 Pa s and µ = 0.001 Pa s, and a non-Newtonian shear-thinning fluid (Bird-Carreau relationship with n = 0.41, λ = 0.1, η∞ = 5.01 × 10(-9) Pa s and η0 = 0.65 Pa s) were investigated. It was found that both the type of contraction and chyme rheology significantly affected the flow and subsequent efficiency of advective motions in the intestinal core. Results also showed that shear rates generated were too small to unveil the pseudo-plastic behaviour of the non-Newtonian fluid. Of the longitudinal motions analysed, the oral propagation was the one leading to the higher, but also the most localised levels of stretching in the rabbit small intestine. This oral propagation was largely characterised by an ordered axial flow and was able to facilitate mixing by stretching material elements in the vicinity of the intestinal wall, particularly in the case of a low viscous water like fluid.