Modelling the breakdown mechanics of solid foods during gastric digestion

Solid food disintegration within the stomach has a major role on the rate and final bioavailability of nutrients within the body. Understanding the link between food material properties and their behaviour during gastric digestion is key to the design of novel structures with enhanced functionalities. However, despite extensive research, the establishment of proper relationships has proved difficult. This work builds on the hypothesis that to bridge this knowledge gap a better understanding of the underlying mechanisms of food disintegration during digestion is needed. The purpose of this study is to propose a new protocol that, by uncoupling the physicochemical processes occurring during gastric digestion, allows for a more rigorous understanding of these mechanisms. Using steamed potatoes as a product model, this study aims to develop a viable methodology to characterize the role of gastric juice and compressive forces on the breakdown mechanics of solid foods during digestion. From a general viewpoint, this work not only reveals the importance of the parameter used to describe the size distribution of food particles on the interpretation of their breakdown behaviour, but also provides a new framework to characterize the mechanisms involved. Results also illustrate that food breakdown during gastric digestion might well not follow a unimodal behaviour, highlighting the need to characterize their performance based on parameters describing broad aspects of their particle size distribution rather than single point values. Arguably simplistic on its approach, this study illustrates how an improved understanding of the role of chemical and physical processes on the breakdown mechanics of solid foods can facilitate valid inferences with respect to their in-vivo performance during digestion. In particular, it shows that while the contraction forces occurring in the stomach can easily disintegrate the potato matrix at the molecular level, the continuous exposure to gastric juices will promote their disintegration into progressively smaller debris. A discussion on the challenges and future directions for the implementation of a more general and standardized protocol is provided. Not intended to reproduce the breakdown behaviour of foods during gastric digestion, but rather to characterize the mechanisms involved, the proposed protocol would open new opportunities to identify the material properties governing the performance of different foods upon ingestion.     

Bolus Formation and Disintegration during Digestion of Food Carbohydrates

Abstract: The first step in the digestion process is mastication, or chewing, when food is broken down, lubricated with saliva, and formed into a cohesive mass known as the food bolus. Upon swallowing, the bolus moves to the stomach and undergoes further breakdown during gastric digestion. The subject of this review is the formation of the food bolus and its subsequent breakdown in the stomach. Bolus formation has been widely studied, especially in terms of food particle size and lubrication. However, information about bolus disintegration is limited, and this review focuses on the breakdown of bread and starch‐based foods. Bolus formation and disintegration are key steps in the overall digestion process, as they control the rate at which ingested food components and nutrients are absorbed and released into the body. Information on the rate kinetics of bolus disintegration is necessary in developing a quantitative understanding of the food digestion process.     

A mathematical model of the effect of pH and food matrix composition on fluid transport into foods: An application in gastric digestion and cheese brining

The question of bioaccessibility of nutrients within a food matrix has become of increasing interest in the fields of nutrition and food science as bioaccessibility is the precursor to bioavailability. By analyzing the propagation of the wetting front of acidic water in raw carrot core and Edam cheese as model systems, we show that the diffusion of the acidic water is dependent on the pH of the gastric fluid and the food matrix. In addition, we demonstrate that the diffusion of NaCl during cheese brining is also dependent upon the concentration of the NaCl. This demonstrates that Fickian diffusion, along with a concentration dependent diffusion coefficient, is a valid model for describing concentration profiles in multiple food systems.Utilizing the diffusion rates found at various pH levels (1.50, 2.00, 3.50, 4.30, 5.25 and 7.00), we developed a model to describe the measured non-linear rate of soluble solid loss during digestion at various constant pH levels. Additionally, we have developed a model to predict the likely rate of soluble solid loss during digestion in the stomach where pH decreases with time. This model can be used to help understand and optimize the relationship between food structure/composition and food degradation in the human stomach, which may help in the development of novel foods with desired functionality.     

Digestion of meat proteins in a human-stomach: A CFD simulation study

Understanding gastric digestion mechanisms is important for the design of functional foods. In this study, we have investigated the meat-protein digestion in human-stomach by using a CFD method. The gastric motility is modeled with a dynamic mesh. The disintegration of large food particles in an acidic environment is simulated using a reaction-diffusion-convection model. A food matrix is used to model the large food-particles. The numerical results show that the digestion and emptying become faster when the meat is treated at a higher temperature. The digestion rate is reduced considerably when the gastric motility or the H⁺ secretion is weakened due to a stomach disorder. TACs stimulate backflows which enhance the transport of enzymes and H⁺, thereby accelerating the digestion process. Due to the flow resistance by the food matrix made of large food particles, liquid gastric contents are emptied in a pathway close to the stomach inner-surface. Large food-particles are mainly disintegrated in the region next to the stomach inner-surface. Therefore, the characteristic length scale of species transport (for enzymes or H⁺) should be the size of food matrix, instead of the size of large food-particles.     

Commercial cheeses with different texture have different disintegration and protein/peptide release rates during simulated in vitro digestion

Solid food disintegration in the stomach has recently been linked to food texture, which changes during digestion. This phenomenon is likely to affect the kinetics of protein digestion and therefore associated postprandial metabolic responses. Depending upon the variety, the cheese protein and lipid content as well as the texture can be modulated, illustrating complexity. Five commercial cheeses, covering a range of textural properties, were selected and characterised. Cheese particles were submitted to an in vitro digestion model to study cheese disintegration and protein/peptide release. Cheese disintegration was affected by cheese texture and composition. At the end of gastric digestion, elastic cheeses (mozzarella) were less disintegrated when compared with ripened and soft cheeses with high fat content (Camembert, aged Cheddar). The protein digestion was different amongst cheeses according to different disintegration rates. Cheese structural and textural properties, attributed to processing parameters, can be used to modulate gastro-intestinal digestion of cheese proteins.     

A human gastric simulator (HGS) to study food digestion in human stomach

The objective of this study was to develop an in vitro stomach model, the Human Gastric Simulator (HGS), for studying gastric digestion of foods. The HGS is designed in such a way as to simulate the continuous peristaltic movement of stomach walls, with similar amplitude and frequency of contraction forces as reported in vivo. The HGS mainly consists of a latex vessel, simulating the stomach chamber, and a series of rollers secured on belts that are driven by motor and pulleys to create a continuous contraction of the latex wall. It also incorporates gastric secretion, emptying systems, and temperature control that enable accurate simulation of dynamic digestion process for detailed investigation of the changes in the physical chemical properties of ingested foods. The simulated gastric contraction force demonstrates a similar pattern as in vivo stomach forces. The precise control of gastric secretion and emptying and the adjustable mechanical forces in the HGS provide a useful tool to study transformation of food constituents under simulated physiological conditions.     

Structural breakdown of starch-based foods during gastric digestion and its link to glycemic response: In vivo and in vitro considerations

The digestion of starch-based foods in the small intestine as well as factors affecting their digestibility have been previously investigated and reviewed in detail. Starch digestibility has been studied both in vivo and in vitro, with increasing interest in the use of in vitro models. Although previous in vivo studies have indicated the effect of mastication and gastric digestion on the digestibility of solid starch-based foods, the physical breakdown of starch-based foods prior to small intestinal digestion is often less considered. Moreover, gastric digestion has received little attention in the attempt to understand the digestion of solid starch-based foods in the digestive tract. In this review, the physical breakdown of starch-based foods in the mouth and stomach, the quantification of these breakdown processes, and their links to physiological outcomes, such as gastric emptying and glycemic response, are discussed. In addition, the physical breakdown aspects related to gastric digestion that need to be considered when developing in vitro–in vivo correlation in starch digestion studies are discussed. The discussion demonstrates that physical breakdown prior to small intestinal digestion, especially during gastric digestion, should not be neglected in understanding the digestion of solid starch-based foods.     

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.     

Biomimetic plant foods: Structural design and functionality

BackgroundThe rising number of people living with chronic conditions, such as diabetes and cardiovascular disease, along with the widespread demand for healthier foods have posed significant challenges to the food industry. Plant-based foods, beyond simple nutrition, can provide health-benefiting functionalities within the complex environment of the human gastrointestinal (GI) tract. Biomimetics is defined as taking inspirations from nature to solve problems. Biomimetic plant foods (BPFs) can offer solutions for the future with the design of nature-inspired food structures for improved health and well-being.Scope and approachThis review provides an insight into the assembly of plant food structures and their disassembly in the human GI tract. Their role in controlling the digestive fate of nutrients is elucidated. Recent developments and future perspectives on designing BPFs are also presented and discussed.Key findings and conclusionsPlant foods in nature possess hierarchically self-assembled structures. During processing and GI digestion, these structures are disassembled to enable liberation and assimilation of nutrients and bioactive molecules contained within the food matrix. The assembly and disassembly are linked to a hierarchy of structure in plants within which different levels (molecule, polymer, cell wall, cell, tissue, organ) and their interactions can modulate nutrient bioaccessibility and digestion. Inspired by nature, BPFs can be engineered to deliver in-body functionality. The emerging trend of biomimetics will potentially pave the way for the future of food.     

Structural changes in milk from different species during gastric digestion in piglets

This study investigated the structural and physicochemical changes that occur in milk, a naturally designed complex structured emulsion, during gastric digestion using the bottle-fed piglet as an animal model. The gastric digestions of cow, goat, and sheep milk were compared in male piglets euthanized at different postfeeding times to collect the stomach chyme. The cow and noncow milks separated into curd (aggregated caseins) and liquid (mostly soluble whey) phases in the piglet's stomach. For milk from all the species, the curd remained longer in the stomach because of its slow disintegration, whereas the liquid phase emptied readily. The majority of the fat globules were found to be entrapped within the protein network of the curd. The rate of release of fat globules was strongly dependent on the breakdown of the surrounding protein network of the curd. The consistency of the gastric curds changed as digestion progressed, with goat and sheep milk curds having relatively softer curd consistency and less fused protein networks, especially toward the end of digestion. This might have led to the lower protein and fat retention in the goat and sheep milk curds and relatively faster gastric emptying of these nutrients from goat and sheep milk in comparison to cow milk. This in vivo study provided new and enhanced understanding of the mechanisms of the gastric digestion of milk from different species. It may have implications for developing bioinspired structures for the controlled digestion and delivery of nutrients.     

Human digestion – a processing perspective

The human digestive system is reviewed in the context of a process with four major unit operations: oral processing to reduce particle size and produce a bolus; gastric processing to initiate chemical and enzymatic breakdown; small intestinal processing to break down macromolecules and absorb nutrients; and fermentation and water removal in the colon. Topics are highlighted about which we need to know more, including effects of aging and dentition on particle size in the bolus, effects of different patterns of food and beverage intake on nutrition, changes in saliva production and composition, mechanical effects of gastric processing, distribution of pH in the stomach, physicochemical and enzymatic effects on nutrient availability and uptake in the small intestine, and the composition, effects of and changes in the microbiota of the colon. Current topics of interest including food synergy, gut–brain interactions, nutritional phenotype and digestion in the elderly are considered. Finally, opportunities for food design based on an understanding of digestive processing are discussed. © 2015 Society of Chemical Industry     

Survival of Lactobacillus rhamnosus strains inoculated in cheese matrix during simulated human digestion

Survival of probiotic bacteria during transit through the gastrointestinal (GI) tract is influenced by a number of environmental variables including stomach acidity, bile salts, digestive enzymes and food matrix. This study assessed survival of seven selected Lactobacillus rhamnosus strains delivered within a model cheese system to the human upper GI tract using a dynamic gastric model (DGM). Good survival rates for all tested strains were recorded during both simulated gastric and duodenal digestion. Strains H12, H25 and N24 demonstrated higher survival capacities during gastric digestion than L. rhamnosus GG strain used as control, with H12 and N24 continuing to grow during duodenal digestion. Strains L. rhamnosus F17, N24 and R61 showed adhesion properties to both HT-29 and Caco-2 cells. The ability to attach to the cheese matrix during digestion was confirmed by scanning electron microscopy, also indicating production of extracellular polysaccharides as a response to acid stress.     

Acid and moisture uptake in steamed and boiled sweet potatoes and associated structural changes during in vitro gastric digestion

Orange-fleshed sweet potatoes are a good source of phytochemicals. For these nutrients to be absorbed, they must be released from the food matrix as a result of physical and chemical breakdown. A key factor in food breakdown is gastric acid diffusion into the matrix, and its influence on structural changes. Cooking treatment may influence mass transport properties and structural changes of foods during digestion. The objective of this study was to determine the acid and moisture uptake into sweet potatoes and its influence on macro- and micro-structures during in vitro gastric digestion as a result of varying cooking treatments. Sweet potatoes were cut into cubes and cooked (boiled or steamed) for different times. In vitro oral and gastric digestions were simulated in a shaking water bath at 37 °C. Acidity, moisture content, and solid loss were measured after 9 digestion times (15 to 240 min). Hardness of individual cubes and microstructure (light microscopy) were completed before and after digestion. Effective diffusivity of acid and moisture into the cubes was estimated using MATLAB. Cooking method, cooking severity, and digestion time significantly influenced moisture uptake (p < 0.0001). Acid uptake was significantly influenced by digestion time (p < 0.0001). The change of softening after digestion was influenced by cooking method and severity (p < 0.05). Effective diffusivity of acid ranged from 0.03 × 10^− 10 (mild steamed) to 11.40 × 10^− 10 m²/s (severely boiled). Percent texture decrease after digestion from the initial hardness ranged from 16% (severely steamed) to 34% (mild boiled). Textural changes were related to cell wall breakdown and starch degradation. In general, mass transport properties and macro- and microstructural changes were influenced by cooking treatment and gastric digestion. The link between food cooking and behavior during digestion is crucial in determining optimal food processing and cooking methods for specific food functional properties.     

粮谷类低血糖生成指数食品研究进展

血糖生成指数（glycemic index,GI）低的食品可以帮助人控制食欲并延缓饥饿,利于控制体重,改善餐后葡萄糖和脂质水平,但是GI值受多种因素影响。因此,本文从营养成分、加工方式等角度综述了食品原料中的淀粉、蛋白质、脂质、功能因子之间的相互作用,以及不同加工方式导致食品GI值的变化,旨在通过对比讨论为开发低GI食品提供理论参考。同时对食品GI值的检测方法进行阐述,GI值的检测已不局限于人体实验测定,出现了更加便捷的体外消化实验测定,已被广泛应用于低GI食品的开发和检测。     

Interfacial design of protein-stabilized emulsions for optimal delivery of nutrients

Proteins are often used as ingredients in food emulsions, as their amphiphilic structures provide electrostatic and steric stabilization. Significant attention has recently been directed at understanding how the composition and structure of oil-water interfaces change during digestion and how these can be manipulated to enhance the delivery of nutrients contained within the oil droplets. These efforts have necessitated the development of more sophisticated in vitro digestion models of greater physiological relevance and increased efforts in research to identify the role of the various digestive parameters on interfacial dynamics. The changes occurring at the oil-water interface will affect the adsorption of gastro-intestinal lipases and, ultimately, affect lipid digestion. The composition of a protein-stabilized oil droplet changes continuously during digestion, because of proteolysis and the formation of peptides with different affinities for the interface. In addition, natural bio-surfactants such as phospholipids and bile salts, other surface- active molecules present in foods, and the products of lipolysis (i.e. mono and diglycerides, lysophospholipids), all compete for access to the interface, and contribute to the dynamic changes occurring on the surface of the oil droplets. A better understanding of how to tailor the composition of oil droplet surfaces in food emulsions will aid in optimizing lipid digestion and, as a result, delivery of lipophilic nutrients. This review focuses on the physico-chemical changes occurring in protein-stabilized oil-in-water emulsions during gastric and small intestine digestion, and on how interfacial engineering could lead to differences in fatty acid release and the potential bioavailability of lipophilic molecules.     

Particle Size Distribution of Brown and White Rice during Gastric Digestion Measured by Image Analysis

The particle size distribution of foods during gastric digestion indicates the amount of physical breakdown that occurred due to the peristaltic movement of the stomach walls in addition to the breakdown that initially occurred during oral processing. The objective of this study was to present an image analysis technique that was rapid, simple, and could distinguish between food components (that is, rice kernel and bran layer in brown rice). The technique was used to quantify particle breakdown of brown and white rice during gastric digestion in growing pigs (used as a model for an adult human) over 480 min of digestion. The particle area distributions were fit to a Rosin–Rammler distribution function. Brown and white rice exhibited considerable breakdown as the number of particles per image decreased over time. The median particle area (x₅₀) increased during digestion, suggesting a gastric sieving phenomenon, where small particles were emptied and larger particles were retained for additional breakdown. Brown rice breakdown was further quantified by an examination of the bran layer fragments and rice grain pieces. The percentage of total particle area composed of bran layer fragments was greater in the distal stomach than the proximal stomach in the first 120 min of digestion. The results of this study showed that image analysis may be used to quantify particle breakdown of a soft food product during gastric digestion, discriminate between different food components, and help to clarify the role of food structure and processing in food breakdown during gastric digestion.     

Eulerian-Lagrangian finite element modelling of food flow-fracture in the stomach to engineer digestion

Highly processed foods tend to form weak structures which breakdown rapidly in the gastrointestinal (GI) tract, often causing negative effects on human metabolism and health. Developing healthier foods has been limited by the lack of understanding of how foods are digested. Through computational modelling we reveal mechanical gastric food breakdown phenomena and relate food mechanical properties with performance during critical initial digestion stages. Our model relies strictly on a viscoplastic-damage constitutive law, calibrated via rheological experiments on an artificial biscuit bolus and validated by simulating cutting tests. Simulations suggest that bolus separation during bolus backward extrusion and/or indentation by peristaltic waves, and, bolus agglomeration due to hydrostatic compression near the pylorus, are two competing phenomena that can influence the bolus free surface to volume ratio. This showcases the importance of including mechanical aspects of breakdown when designing foods for controlled chemo-mechanical breakdown and associated nutrient release rates.     

An integrated look at the effect of structure on nutrient bioavailability in plant foods

The true bioavailability of a nutrient being intrinsically coupled to the specific food matrix in which it occurs remains poorly considered in nutrition science. During digestion, the food matrix and, in particular, the structure of food modulate the extent and kinetics to which nutrients and bioactive compounds make themselves available for absorption. In this perspective, we describe an integrated look at the effect of structure on nutrient bioavailability in plant foods. Based on this integrated look, cell wall integrity and the particle size of the plant material during its transit in the small intestine determine the bioavailability of plant nutrients; in turn, cell wall integrity and particle size are determined by the level of oral processing and, accordingly, what subsequently escapes digestion in the upper intestine and is utilized by colon microbiota. Ultimately, the effect on nutrient digestion is linked to food structure through each step of digestion. A consideration of the structure rather than just the composition of foods opens up possibilities for the design of healthier foods. © 2018 Society of Chemical Industry     

Roles for dietary fibre in the upper GI tract: The importance of viscosity

Dietary fibre has long been recognised as healthy because of its prebiotic quality and a number of dietary fibres, especially beta glucan have been shown to lower levels of circulating LDL cholesterol. However, although EFSA allow health claims to be made for this, there is no fundamental understanding of the detailed mechanism involved. More recently dietary fibre has been shown to have a range of functionality in the upper GI tract. The presence of fibre can alter gastric emptying thus affecting fullness and satiety. These alterations are a result of differences in viscosity, nutrient release and nutrient sensing in the duodenum. The current proposed mechanisms for the cholesterol lowering effects involve disruption of the normal recycling of bile possibly by sequestering bile salts and fatty acids or by significantly decreasing the rate of absorption as a result of entanglement with intestinal mucus.The use of quantitative confocal microscopy methods such as fluorescence recovery after photobleaching (FRAP) and multiple particle tracking has provided evidence that dietary fibre can combine with intestinal mucus and produce a layer that significantly delays the transport of lipid digestion products. We have also used similar methods in conjunction with more conventional rheology to show that DNA from the gut epithelium can contribute significantly to the barrier properties of the intestinal mucus layer.The delay in the transport of nutrients to the gut epithelium has implications for the control of gastric emptying and through secretion of GI hormones such as CCK and thus for the satiating ability of foods. It may also have implications for the reabsorption of bile.