Breakdown mechanisms of whey protein gels during dynamic in vitro gastric digestion.

Breakdown of solid foods during gastric digestion plays a major role in the release and absorption of nutrients in the gastrointestinal tract. The breakdown mechanisms of foods during gastric digestion may be influenced by composition, particle geometry, and the resulting moisture uptake and gastric emptying. The extent of breakdown may have implications on the pH, pepsin activity, and subsequent protein hydrolysis. This study aims to identify the influence of particle geometry on pH, buffering capacity, and breakdown mechanisms during in vitro dynamic gastric digestion. Whey protein gels made in different geometries (small, medium, and large cubes with side lengths of 3.1, 5.2, and 10.3 mm, respectively, and spheres with a diameter of 6.5 mm) were subjected to gastric digestion using the Human Gastric Simulator (HGS) over a 180 min period. Particle size in the bulk digesta showed the breakdown mechanism of spheres was primarily by erosion, whereas breakdown of cubes was by fragmentation at the beginning of digestion, followed by erosion. Moisture uptake and gastric emptying of dry matter were significantly influenced by digestion time, particle geometry, and their interaction (p < 0.001). Initial buffering capacity of the gels was highest in small cubes and lowest in large cubes, causing the pH to decrease faster in large cubes. There was a higher pepsin activity in the liquid phase of the digesta in large cubes compared to the rest of the treatments, which was hypothesized to be due to a diffusion limitation of pepsin, resulting in less diffusion into large cubes due to their lower total specific surface area. Further work is needed to develop quantitative connections between food initial properties, breakdown mechanisms, and their implications on pH, pepsin activity, and nutrient digestibility for future food design.

Food buffering capacity: quantification methods and its importance in digestion and health.

The complex relationship between food properties and their behavior during human digestion is not well understood. During gastric digestion, food chemical and physical breakdown occurs as a result of gastric secretions and peristaltic contractions, respectively. Food breakdown is modulated through food properties such as physicochemical composition and macro-structure, including texture and viscosity. Another food property that may play a crucial role in food chemical breakdown and gastric secretions, but has been largely disregarded in previous studies, is food buffering capacity. Buffering capacity is a characteristic of foods due to the presence of acid/base groups, which causes a resistance to change pH after additions of acid or alkali. Buffering capacity of food has been studied in different applications, including for production of human food and animal feed, as well as for human health applications, including gastric digestion, gastroesophageal reflux disease, development of drugs and pharmaceuticals, food allergenicity, and dental health. However, a limitation for widespread adoption of buffering capacity measurements is a standard method, as results from many previous studies are not directly comparable and use different measurement and quantification methods. The relationship between food composition and physical properties with buffering capacity as well as how food buffering capacity may influence gastric secretions and gastric emptying during digestion are not well-characterized. The development of a fundamental understanding of the influence of food properties on buffering capacity and its impact on gastric secretions and breakdown during digestion are needed for improvement of future digestion studies and for optimization of functional foods. The importance of buffering capacity in food digestion processes, such as gastric secretions and food breakdown, is described in this review, as well as a description of methods previously used to quantify buffering capacity during in vitro and in vivo digestion.

Buffering capacity of commercially available foods is influenced by composition and initial properties in the context of gastric digestion.

Buffering capacity is defined as the ability of a material to resist changes in pH after addition of acid or alkali. Food buffering capacity is important to consider during gastric digestion as it will impact the intragastric pH and gastric secretion rate. These factors will further influence the pepsin activity and acid hydrolysis, which will ultimately impact food breakdown and gastric emptying. The objective of this study was to determine the influence of composition and initial properties of thirty commercially available foods on buffering capacity. Protein content, fat content, particle size distribution, and buffering capacity were measured. A regression model was developed to evaluate which of the tested properties had the greatest contribution to the food buffering capacity. Overall, protein content and initial pH of the food were the most important factors in determination of buffering capacity. Foods were then classified into 6 classes based on their protein content. Foods in class 6, with higher protein content (average 22.3%), had significantly higher buffering capacity than foods in class 1, with lowest buffering capacity (average 0.6% protein) (p < 0.0001). Within dairy and meat products, higher fat content produced a lower buffering capacity. The interaction between initial properties and composition also influenced buffering capacity. For example, buffering capacity in foods with low protein content (<1.4%) was influenced by the organic acid content and initial pH. Particle size was an important factor for buffering capacity, but its role is influenced by protein content. Understanding the key factors contributing to the buffering capacity of foods is crucial for digestion studies as it will impact physicochemical and enzymatic reactions during digestion.

Pearl millet (Pennisetum glaucum) couscous breaks down faster than wheat couscous in the Human Gastric Simulator, though has slower starch hydrolysis.

Consumption of traditional West African pearl millet (Pennisetum glaucum) couscous delayed gastric emptying in our recent human study compared to other starch-based foods (white rice, boiled potatoes, pasta). The objective of this study was to determine whether physical properties of pearl millet couscous affect particle breakdown and starch hydrolysis during simulated gastric digestion to understand the basis of the slow gastric emptying. Starch fine structure and viscosity were analyzed for initial millet and wheat couscous samples by high performance size-exclusion chromatography and the Rapid Visco Analyzer, respectively. Couscous samples were subjected to simulated gastric digestion using the Human Gastric Simulator (HGS), a dynamic model of human gastric digestion. Digesta was collected from the HGS at 30 min intervals over 180 min. Particle size and percent starch hydrolysis of couscous in the digesta were evaluated at each time point. The number of particles per gram of dry mass substantially increased over digestion time for millet couscous (p < 0.05), while changed little for the wheat couscous samples. Millet couscous showed lower starch hydrolysis per unit surface area of particles than wheat couscous (p < 0.05). Slower starch hydrolysis was associated with smaller (p < 0.05) amylose chain length for millet (839-963 DP) than for wheat (1225-1563 DP), which may enable enable a denser packing of millet starch molecules that impedes hydrolysis. We hypothesize that the slow gastric emptying rate of millet couscous observed in humans may be explained by its slow starch hydrolysis property that could activate the ileal brake system, independent of high particle breakdown rate in the stomach.

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.

Fresh-Squeezed Orange Juice Properties Before and During In Vitro Digestion as Influenced by Orange Variety and Processing Method.

This study aims to analyze the influence of processing and orange variety on initial quality, antioxidant activity, total polyphenol content (TPC), and ascorbic acid content of fresh-squeezed orange juice during in vitro digestion. Fresh-squeezed orange juice was made from Fukumoto Navel, Lane Late Navel, Olinda Nucellar Valencia, and Campbell Valencia oranges, and was processed thermally and nonthermally. Antioxidant activity (FRAP and ABTS assays), TPC (Folin-Ciocalteu method), and ascorbic acid were analyzed before and after gastrointestinal digestion. Bioaccessibility was calculated by comparing the measured values after digestion with the initial value for each juice. Orange variety significantly influenced pH, acidity, and total soluble solids (P < 0.0001). Antioxidant activity by FRAP was significantly higher (P < 0.0001) in Fukumoto Navel orange juice (16.0 ± 0.4 mM Trolox) than the other juices (range: 9.1 to 10 mM Trolox). TPC was significantly influenced by orange variety (P < 0.0001) and ranged from 521 ± 6 (Campbell Valencia) to 800 ± 11 mg gallic acid/L (Lane Late Navel). Processing method did not influence antioxidant and polyphenol bioaccessibility (P > 0.05). However, antioxidant activity by ABTS and ascorbic acid bioaccessibility were significantly influenced by orange variety (P < 0.0001). These results indicate that fruit variety and nutrient bioaccessibility should be considered to optimize processing and formulation parameters. PRACTICAL APPLICATION: Processing method and variety of fruit during beverage manufacturing may influence its nutrient bioaccessibility. We present a detailed examination of the influence of orange variety, harvest time, and processing method on initial quality parameters and antioxidant bioaccessibility. It is recommended that nutritional analysis of beverages take into consideration both the bioaccessibility of nutrients and the initial nutrient content of the beverage. These results can be used for juice processors to take into consideration the harvest season and produce variety to manufacture beverages with higher nutritional quality.

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.