Cooked Rice-Based and Wheat-Based Food Structure Influenced Digestion Kinetics and Glycemic Response in Growing Pigs.

BACKGROUND: How starch-based food structure can affect the rate and extent of digestion in the small intestine and resulting glycemic response is not properly understood. One possible explanation is that food structure influences gastric digestion, which subsequently determines digestion kinetics in the small intestine and glucose absorption. However, this possibility has not been investigated in detail. OBJECTIVES: Using growing pigs as a digestion model for adult humans, this study aimed to investigate how physical structure of starch-rich foods affects small intestinal digestion and glycemic response. METHODS: Male growing pigs (21.7 ± 1.8 kg, Large White × Landrace) were fed one of the 6 cooked diets (250-g starch equivalent) with varying initial structures (rice grain, semolina porridge, wheat or rice couscous, or wheat or rice noodle). The glycemic response, small intestinal content particle size and hydrolyzed starch content, ileal starch digestibility, and portal vein plasma glucose were measured. Glycemic response was measured as plasma glucose concentration collected from an in-dwelling jugular vein catheter for up to 390 min postprandial. Portal vein blood samples and small intestinal content were measured after sedation and euthanasia of the pigs at 30, 60, 120, or 240 min postprandial. Data were analyzed with a mixed-model ANOVA. RESULTS: The plasma glucose Δmaxoverall and iAUCoverall for couscous and porridge diets (smaller-sized diets) were higher than that of intact grain and noodle diets (larger-sized diets): 29.0 ± 3.2 compared with 21.7 ± 2.6 mg/dL and 5659 ± 727 compared with 2704 ± 521 mg/dL⋅min, for the smaller-sized and larger-sized diets, respectively (P < 0.05). Ileal starch digestibility was not significantly different between the diets (P ≥ 0.05). The iAUCoverall was inversely related to the starch gastric emptying half-time of the diets (r = -0.90, P = 0.015). CONCLUSIONS: Starch-based food structure affected the glycemic response and starch digestion kinetics in the small intestine of growing pigs.

Progress and challenges in designing dynamic in vitro gastric models to study food digestion.

Understanding the mechanisms involved in food breakdown in the human gastrointestinal (GI) tract is essential in food digestion research. Research to study food digestion in the human GI tract requires in vivo and in vitro approaches. In vivo methods involving human or animal subjects are often cost-prohibitive and raise ethical concerns. For these reasons, in vitro approaches are becoming more common. Several dynamic in vitro models that mimic one or more components of the GI tract have been developed at various research institutions and by commercial companies. While there is evidence of considerable novelty and innovation in the design of these models, there are many differences among them in how the mechanical breakdown of solid foods is accomplished. In some systems, modulating water pressure is used to achieve peristaltic contractions of the gastric antrum, whereas, in other models, the flexible walls of a gastric chamber are compressed by the movement of rollers or clamps outside the walls of the test chamber. Although much progress has been made in standardizing the biochemical environment appropriate to the food digestion process, there is a lack of standard protocols to measure mechanical forces that result in the breakdown of solid foods. Similarly, no standardized methods are available to evaluate the results obtained from in vitro trials for validation purposes. Due to the large variability in the design features of in vitro models used for food digestion studies, developing consensus-based standards for the mechanical aspects of food breakdown is needed.

Gastric emptying rate and chyme characteristics for cooked brown and white rice meals in vivo.

BACKGROUND: Rice structure is important to rice grain and starch breakdown during digestion. The objective of this study was to determine the gastric emptying and rice composition during gastric digestion of cooked brown and white medium-grain (Calrose variety) rice using the growing pig as a model for the adult human. RESULTS: Brown and white rice did not show significantly different gastric emptying rates of dry matter or starch, but brown rice had slower protein emptying (P < 0.05). Moisture content was greater and pH was lower in the distal stomach compared to the proximal stomach (P < 0.0001), and varied with time (P < 0.0001). The mechanism of physical breakdown for brown and white rice varied. Brown rice exhibited an accumulation of bran layer fragments in the distal stomach, quantified by lower starch and higher protein content. CONCLUSION: The quantity of gastric secretions observed after a brown or white rice meal may be related to the meal buffering capacity, and are accumulated in the distal stomach. The delayed rate of protein emptying in brown rice compared to white rice was most likely due to the accumulation of bran layers in the stomach.

Contribution of the proximal and distal gastric phases to the breakdown of cooked starch-rich solid foods during static in vitro gastric digestion.

In vitro gastric digestion studies commonly focus on the acidic environment of the stomach (the distal phase), neglecting that the contact time between food and salivary amylase can be extended during bolus' temporary storage in the proximal stomach (the proximal phase). Consequently, the role of the proximal phase of gastric digestion on the breakdown of solid starch-based foods is not well understood. This study aimed to address this question using a static in vitro digestion approach. Cooked starch-rich foods of different physical structures (wheat couscous, wheat pasta, rice couscous, rice noodle, and rice grain) were subjected to 30 s oral phase digestion, followed by prolonged incubation of the oral phase mixture (pH 7) for up to 30 min representing different proximal phase digestion times. Each proximal phase sample was sequentially incubated in excess simulated gastric fluid (distal phase, pH 2) for up to an additional 180 min. The proximal phase aided solid food breakdown through starch hydrolysis that caused leaching of particles <2 mm. The distal phase led to softening of food particles, but the softening process was not enhanced with longer proximal phase. In foods with smaller initial size (couscous and rice couscous), a proximal phase of 15 min or longer followed by 180-min distal phase increased starch hydrolysis in the liquid and suspended solid fractions of the digesta, indicating the influence of food structure on acid hydrolysis during in vitro gastric digestion.

Influence of food macrostructure on the kinetics of acidification in the pig stomach after the consumption of rice- and wheat-based foods: Implications for starch hydrolysis and starch emptying rate.

How the stomach can serve as a biochemical environment for starch digestion and the implications on starch emptying are not well-understood. Biochemical changes during gastric digestion of cooked wheat- and rice-based diets of varying particle size and microstructure were investigated using a growing pig model. In larger-particle size diets (rice grain, rice noodle, pasta), pH >3 was maintained in the proximal stomach digesta even until 240 min digestion, resulting in extended remaining amylase activity and accumulation of maltose from starch hydrolysis in the stomach. In smaller-particle size diets (couscous, rice couscous, semolina porridge), gastric acidification occurred faster to produce homogeneous intragastric pH and deactivated amylase. The hypothesis of the study was that food macrostructure would impact gastric acidification kinetics, and the resulting biochemical environment for starch hydrolysis in the stomach may further affect the mechanisms of food breakdown in the stomach and gastric emptying of starch.

Correction: Tracking physical breakdown of rice- and wheat-based foods with varying structures during gastric digestion and its influence on gastric emptying in a growing pig model.

Correction for 'Tracking physical breakdown of rice- and wheat-based foods with varying structures during gastric digestion and its influence on gastric emptying in a growing pig model' by Joanna Nadia et al., Food Funct., 2021, DOI: 10.1039/D0FO02917C.

Tracking physical breakdown of rice- and wheat-based foods with varying structures during gastric digestion and its influence on gastric emptying in a growing pig model.

There is currently a limited understanding of the effect of food structure on physical breakdown and gastric emptying of solid starch-based foods during gastric digestion. Moisture uptake, pH, particle size, rheological, and textural properties of six solid starch-based diets from different sources (Durum wheat and high amylose white rice) and of different macrostructures (porridge, native grain, agglomerate/couscous, and noodle) were monitored during 240 min of gastric digestion in a growing pig model. Changes in the physical properties of the gastric digesta were attributed to the influence of gastric secretions and gastric emptying, which were both dependent on the buffering capacity and initial macrostructure of the diets. Differences between the proximal and distal stomach regions were found in the intragastric pH and texture of the gastric digesta. For example, rice couscous, which had the smallest particle size and highest buffering capacity among the rice-based diets, had the shortest gastric emptying half-time and no significant differences between proximal and distal stomach digesta physical properties. Additionally, a relationship between gastric breakdown rate, expressed as gastric softening half-time from texture analysis, and gastric emptying half-time of dry matter was also observed. These findings provide new insights into the breakdown processes of starch-based solid foods in the stomach, which can be beneficial for the development of food structures with controlled rates of breakdown and gastric emptying during digestion.

Buffering capacity of protein-based model food systems in the context of gastric digestion.

Buffering capacity is a characteristic of foods to resist changes in pH, which is important to consider in gastric digestion as it will impact physicochemical breakdown of food. A standardized method to measure and quantify buffering capacity in the context of digestion is needed to improve in vitro digestion studies by providing a better estimation of acid secretions and subsequent protein digestibility. The objective of this study was to develop a method to measure buffering capacity in the context of digestion and develop a regression model to predict buffering capacity using protein-based model foods. Buffering capacity was analyzed by titrating 0.16 M HCl to egg and whey-protein based dispersions and gels of varying protein content and particle size and recording the pH after each addition. Calculated parameters from buffering capacity experiments included total acid added, area under the curve, total buffering capacity, relative [H+] increase, and lag phase. A regression model was developed to predict each buffering capacity parameter based on protein concentration, specific surface area, aspartic acid and glutamic acid content. Results showed that higher protein concentration and smaller surface area resulted in higher buffering capacity. A validation dataset was used to evaluate the goodness of fit of the model to the data with different protein concentrations, surface area or protein source. Results indicated that total buffering capacity and lag phase parameters can be used to quantify buffering capacity of protein gels in the context of digestion, since they provided a good fit to the observational and validation data sets.

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.

INFOGEST static in vitro simulation of gastrointestinal food digestion.

Developing a mechanistic understanding of the impact of food structure and composition on human health has increasingly involved simulating digestion in the upper gastrointestinal tract. These simulations have used a wide range of different conditions that often have very little physiological relevance, and this impedes the meaningful comparison of results. The standardized protocol presented here is based on an international consensus developed by the COST INFOGEST network. The method is designed to be used with standard laboratory equipment and requires limited experience to encourage a wide range of researchers to adopt it. It is a static digestion method that uses constant ratios of meal to digestive fluids and a constant pH for each step of digestion. This makes the method simple to use but not suitable for simulating digestion kinetics. Using this method, food samples are subjected to sequential oral, gastric and intestinal digestion while parameters such as electrolytes, enzymes, bile, dilution, pH and time of digestion are based on available physiological data. This amended and improved digestion method (INFOGEST 2.0) avoids challenges associated with the original method, such as the inclusion of the oral phase and the use of gastric lipase. The method can be used to assess the endpoints resulting from digestion of foods by analyzing the digestion products (e.g., peptides/amino acids, fatty acids, simple sugars) and evaluating the release of micronutrients from the food matrix. The whole protocol can be completed in ~7 d, including ~5 d required for the determination of enzyme activities.

Gastric protein hydrolysis of raw and roasted almonds in the growing pig.

Gastric protein hydrolysis may influence gastric emptying rate and subsequent protein digestibility in the small intestine. This study examined the gastric hydrolysis of dietary protein from raw and roasted almonds in the growing pig as a model for the adult human. The gastric hydrolysis of almond proteins was quantified by performing tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent image analysis. There was an interaction between digestion time, stomach region, and almond type for gastric protein hydrolysis (p<0.05). Gastric emptying rate of protein was a significant (p<0.05) covariate in the gastric protein hydrolysis. In general, greater gastric protein hydrolysis was observed in raw almonds (compared to roasted almonds), hypothesized to be related to structural changes in almond proteins during roasting. Greater gastric protein hydrolysis was observed in the distal stomach (compared to the proximal stomach), likely related to the lower pH in the distal stomach.

Acid diffusion into rice boluses is influenced by rice type, variety, and presence of α-amylase.

Breakdown of rice during gastric digestion may be influenced by rice structure, presence of salivary α-amylase, and hydrolysis by gastric acid. During mastication, saliva is mixed with rice, allowing α-amylase to begin starch hydrolysis. This hydrolysis may continue in the gastric environment depending on the rate at which gastric acid penetrates into the rice bolus. The objective of this study was to determine the acid uptake into rice boluses with and without α-amylase in saliva. Two types each of brown and white rice (medium and long grain), were formed into a cylindrical-shaped bolus. Each bolus was sealed on all sides except one to allow one-dimensional mass transfer, and incubated by immersion in simulated gastric juice at 37 °C under static conditions. Acidity of the boluses was measured by titration after 1 to 96 h of incubation. Effective diffusivity of the gastric juice through the bolus was estimated using MATLAB. Average acidity values ranged from 0.04 mg HCl/g dry matter (medium grain white rice, no incubation) to 10.01 mg HCl/g dry matter (long-grain brown rice, 72 h incubation). The rice type, presence of α-amylase, and incubation time all significantly influenced rice bolus acidity (P < 0.001). Effective diffusivity of gastric juice into the bolus was greater in brown rice than in white rice. These results indicate that starch hydrolysis by α-amylase may continue in the stomach before the gastric acid penetrates the rice bolus, and the rate of acid uptake will depend on the type of rice consumed.

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.

Utility of models of the gastrointestinal tract for assessment of the digestion and absorption of engineered nanomaterials released from food matrices.

Engineered metal/mineral, lipid and biochemical macromolecule nanomaterials (NMs) have potential applications in food. Methodologies for the assessment of NM digestion and bioavailability in the gastrointestinal tract are nascent and require refinement. A working group was tasked by the International Life Sciences Institute NanoRelease Food Additive project to review existing models of the gastrointestinal tract in health and disease, and the utility of these models for the assessment of the uptake of NMs intended for food. Gastrointestinal digestion and absorption could be addressed in a tiered approach using in silico computational models, in vitro non-cellular fluid systems and in vitro cell culture models, after which the necessity of ex vivo organ culture and in vivo animal studies can be considered. Examples of NM quantification in gastrointestinal tract fluids and tissues are emerging; however, few standardized analytical techniques are available. Coupling of these techniques to gastrointestinal models, along with further standardization, will further strengthen methodologies for risk assessment.

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.

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 (x(50)) 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.

Gastric digestion of raw and roasted almonds in vivo.

Almonds are an important dietary source of lipids, protein, and α-tocopherol. It has been demonstrated that the physical form of almond kernels influences their digestion and absorption, but the role of thermal processes on the digestion of almonds has received little attention. The objectives of this study were to examine the gastric emptying and nutrient composition of gastric chyme from pigs (used as a model for the adult human) fed a single meal of either raw or roasted almonds over a 12-h postprandial period (72 pigs total, 6 pigs at each diet-time combination). Concentrations of glucose, triacylglycerols, and α-tocopherol in peripheral plasma during the 12-h postprandial period were determined. For dry matter and lipid, the gastric emptying profile was not different between raw and roasted almonds. Roasting almonds also did not influence gastric pH, or plasma glucose or triacylglycerols levels. In contrast, the gastric emptying of protein was more rapid for raw almonds compared to roasted almonds (P < 0.01) and intragastric protein content exhibited segregation (P < 0.001) throughout the stomach, with raw almonds having a higher level of segregation compared to roasted almonds. Postprandial plasma α-tocopherol levels were, on average 33% greater (P < 0.001) after consumption of raw almonds, most likely as a result of the higher concentration of α-tocopherol in raw almonds compared to roasted almonds. Roasting of almonds did not influence the overall gastric emptying process, but did lead to differences in the distribution of protein in the stomach and to the gastric emptying of protein.

Release and bioaccessibility of ß-carotene from fortified almond butter during in vitro digestion.

The objective of this study was to determine the release and bioaccessibility of ß-carotene from fortified almond butter using in vitro digestion models. Two types of fortifiers were investigated: ß-carotene oil (oil) and whey protein isolate (WPI)-alginate-chitosan capsules containing ß-carotene oil (capsule). Shaking water bath and Human Gastric Simulator (HGS) digestion models assessed the impact of gastric peristalsis on the release of ß-carotene. Bioaccessibility of ß-carotene was measured as percent recovered from the micelle fraction. There was greater release of ß-carotene from oil fortified almond butter in the HGS model (87.1%) due to peristalsis than the shaking water bath model (51.0%). More ß-carotene was released from capsule fortified almond butter during intestinal digestion. However, more ß-carotene was recovered from the micelle fraction of oil fortified almond butter. These results suggest that a WPI-alginate-chitosan capsule coating may inhibit the bioaccessibility of ß-carotene from fortified almond butter.

Nutritional translation blended with food science: 21st century applications.

This paper, based on the symposium "Real-World Nutritional Translation Blended With Food Science," describes how an integrated "farm-to-cell" approach would create the framework necessary to address pressing public health issues. The paper describes current research that examines chemical reactions that may influence food flavor (and ultimately food consumption) and posits how these reactions can be used in health promotion; it explains how mechanical engineering and computer modeling can study digestive processes and provide better understanding of how physical properties of food influence nutrient bioavailability and posits how this research can also be used in the fight against obesity and diabetes; and it illustrates how an interdisciplinary scientific collaboration led to the development of a novel functional food that may be used clinically in the prevention and treatment of prostate cancer.

Solid Loss of Carrots During Simulated Gastric Digestion.

The knowledge of solid loss kinetics of foods during digestion is crucial for understanding the factors that constrain the release of nutrients from the food matrix and their fate of digestion. The objective of this study was to investigate the solid loss of carrots during simulated gastric digestion as affected by pH, temperature, viscosity of gastric fluids, mechanical force present in stomach, and cooking. Cylindrical carrot samples were tested by static soaking method and using a model stomach system. The weight retention, moisture, and loss of dry mass were determined. The results indicated that acid hydrolysis is critical for an efficient mass transfer and carrot digestion. Internal resistance rather than external resistance is dominant in the transfer of soluble solids from carrot to gastric fluid. Increase in viscosity of gastric fluid by adding 0.5% gum (w/w) significantly increased the external resistance and decreased mass transfer rate of carrots in static soaking. When mechanical force was not present, 61% of the solids in the raw carrot samples were released into gastric fluid after 4 h of static soaking in simulated gastric juice. Mechanical force significantly increased solid loss by causing surface erosion. Boiling increased the disintegration of carrot during digestion that may favor the loss of solids meanwhile reducing the amount of solids available for loss in gastric juice. Weibull function was successfully used to describe the solid loss of carrot during simulated digestion. The effective diffusion coefficients of solids were calculated using the Fick's second law of diffusion for an infinite cylinder, which are between 0.75 × 10(-11) and 8.72 × 10(-11) m(2)/s, depending on the pH of the gastric fluid.