Properties of Gastric Chyme from Pigs Fed Cooked Brown or White Rice

Comparison of four digestion protocols on the physical characteristics of gastric digesta from cooked couscous using the Human Gastric Simulator

In vitro digestion is widely employed in food, nutraceutical and pharmaceutical research, and numerous in vitro gastric digestion protocols have been proposed, with a wide range of experimental conditions. Differences in the simulated gastric fluids (pH, mineral content, enzyme type and enzyme activity) of different digestion protocols may alter the results for the digestion of the same meal. This study aimed to investigate how variations in the gastric secretion rate and composition in four in vitro digestion protocols (Infogest Riddet, Infogest Semi-dynamic, UC Davis and United States Pharmacopeia) impacted the physical properties of the emptied gastric digesta. Cooked couscous was used as a model meal and subjected to simulated gastric digestion using a dynamic gastric model, the Human Gastric Simulator (HGS). The digesta were collected from the outlet of the HGS after 15, 30, 60, 90, 120, 150, or 180 min. The gastric emptying of dry matter, pH, rheological properties, and particle size were evaluated. The digestion protocol significantly influenced the solid content and moisture content of the digesta (p < 0.001), particles per gram of dry matter (p < 0.0001), gastric emptying of dry matter (p < 0.003), shear stress at 0.45 s-1 and consistency coefficient (p < 0.0001). The presence of NaHCO3 in the Infogest Riddet and Infogest Semi-dynamic gastric secretions provided an additional buffering effect and increased the digesta pH during gastric digestion. Similarly, the inclusion of mucin in the UC Davis protocol resulted in a higher flow and viscoelastic properties of the emptied digesta. The highest dilution of gastric content in the United States Pharmacopeia (USP) protocol resulted in larger particles emptied from the HGS and the longest gastric emptying half-time of all digestion protocols. These findings provide new insights into the impact of digestion protocols on the digesta properties, which can be beneficial for the design and standardization of in vitro digestion models.

Evaluation of the performance of the human gastric simulator using durum wheat-based foods of contrasting food structure

The selection of gastric digestion parameters in food digestion studies using in vitro models is critical to properly represent structural changes in the stomach. This study aimed to evaluate the performance of digestion in the human gastric simulator (HGS) using generalized in vitro gastric digestion parameters (secretion rate of 4.1 mL min^-1, gastric emptying rate of 5.68 g min^-1) that were derived from a previous in vivo study using six starch-rich foods. Two of the six foods used in the in vivo study (cooked durum wheat porridge/semolina and pasta) were digested in the HGS for up to 240 min, then the properties of the emptied and remaining digesta were measured. The properties of the in vitro remaining digesta were compared to those measured in vivo (growing pig stomach). The trends in the gastric breakdown rate and mechanisms, dry matter emptying kinetics, and starch hydrolysis of pasta and semolina were similar to those of in vivo. Gastric breakdown and dilution kinetics in vitro and in vivo were well-related but did not have a 1 : 1 correlation, whereas gastric acidification kinetics in the HGS deviated from that observed in vivo. The results suggest that generalized digestion parameters could be used to predict the effect of food structure on in vivo gastric breakdown and emptying, but care should be taken in interpretation of results, as the gastric acidification process was different from what was observed in vivo. This information will help refine in vitro digestion model parameters to provide more physiologically-relevant data in future studies.

Cooked rice- and wheat-based food structure influenced digestion kinetics and glycemic response in growing pigs

BACKGROUND

How starch-based food structure can impact 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 impacts small intestinal digestion and glycemic response.

METHODS

Male growing pigs (21.7 ± 1.8 kg, Large White × Landrace) were fed one of six 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 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 Δmax_overall and iAUC_overall for couscous and porridge diets (smaller-sized diets) were higher than intact grain and noodle diets (larger-sized diets); 29.0 ± 3.2 vs. 21.7 ± 2.6 mg/dL and 5659 ± 727 vs. 2704 ± 521 mg/dL.min, for the smaller- and larger-sized diets, respectively (p < 0.05). Ileal starch digestibility was not significantly different between diets (p ≥ 0.05). The iAUC_overall 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.

Spatial-temporal mapping of the intra-gastric pepsin concentration and proteolysis in pigs fed egg white gels

While there is a consensus that food structure affects food digestion, the underlying mechanisms remain poorly understood. A previous experiment in pigs fed egg white gels of same composition but different structures evidenced such effect on food gastric disintegration. In this study, we detailed the consequences on intra-gastric pH, pepsin concentration and proteolysis by sampling throughout the stomach over 6 h digestion. Subsequent amino acid absorption was investigated as well by blood sampling. While acidification was almost homogeneous after 6 h digestion regardless of the gel, pepsin distribution never became uniform. Pepsin started to accumulate in the pylorus/antrum region before concentrating in the body stomach beyond 4 h, time from which proteolysis really started. Interestingly, the more acidic and soft gel resulted in a soon (60 min) increase in proteolysis, an earlier and more intense peak of plasmatic amino acids, and a final pepsin concentration three times higher than with the other gels.

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.

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.

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

Pearl millet couscous broke down into smaller, more numerous particles that had slower starch hydrolysis compared to wheat couscous.

The Effects of Moderate Whole Grain Consumption on Fasting Glucose and Lipids, Gastrointestinal Symptoms, and Microbiota

This study was designed to determine if providing wheat, corn, and rice as whole (WG) or refined grains (RG) under free-living conditions will change parameters of health over a six-week intervention in healthy, habitual non-WG consumers. Measurements of body composition, fecal microbiota, fasting blood glucose, total cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL), and triglycerides were made at baseline and post intervention. Subjects were given adequate servings of either WG or RG products based on their caloric need and asked to keep records of grain consumption, bowel movements, and GI symptoms weekly. After six weeks, subjects repeated baseline testing. Significant decreases in total, LDL, and non-HDL cholesterol were seen after the WG treatments but were not observed in the RG treatment. During Week 6, bowel movement frequency increased with increased WG consumption. No significant differences in microbiota were seen between baseline and post intervention, although, abundance of order Erysipelotrichales increased in RG subjects who ate more than 50% of the RG market basket products. Increasing consumption of WGs can alter parameters of health, but more research is needed to better elucidate the relationship between the amount consumed and the health-related outcome.

Does Whole Grain Consumption Alter Gut Microbiota and Satiety?

This review summarizes recent studies examining whole grain consumption and its effect on gut microbiota and satiety in healthy humans. Studies comparing whole grains to their refined grain counterparts were considered, as were studies comparing different grain types. Possible mechanisms linking microbial metabolism and satiety are described. Clinical trials show that whole grain wheat, maize, and barley alter the human gut microbiota, but these findings are based on a few studies that do not include satiety components, so no functional claims between microbiota and satiety can be made. Ten satiety trials were evaluated and provide evidence that whole oats, barley, and rye can increase satiety, whereas the evidence for whole wheat and maize is not compelling. There are many gaps in the literature; no one clinical trial has examined the effects of whole grains on satiety and gut microbiota together. Once understanding the impact of whole grains on satiety and microbiota is more developed, then particular grains might be used for better appetite control. With this information at hand, healthcare professionals could make individual dietary recommendations that promote satiety and contribute to weight control.

A review of mixing and propulsion of chyme in the small intestine: fresh insights from new methods

The small intestine is a convoluted flexible tube of inconstant form and capacity through which chyme is propelled and mixed by varying patterns of contraction. These inconstancies have prevented quantitative comparisons of the manner in which contractile activity engenders mixing of contained chyme. Recent quantitative work based on spatiotemporal mapping of intestinal contractions, macro- and micro-rheology, particle image velocimetry and real-time modelling has provided new insights into this process. Evidence indicates that the speeds and patterns of the various types of small intestinal contraction are insufficient to secure optimal mixing and enzymatic digestion over a minimal length of intestine. Hence particulate substrates and soluble nutrients become dispersed along the length of the lumen. Mixing within the lumen is not turbulent but results from localised folding and kneading of the contents by contractions but is augmented by the inconstant spatial disposition of the contractions and their component contractile processes. The latter include inconstancies in the sites of commencement and the directions of propagation of contraction in component groups of smooth muscle cells and in the coordination of the radial and circular components of smooth muscle contraction. Evidence suggests there is ongoing augmentation of mixing at the periphery of the lumen, during both the post-prandial and inter-meal periods, to promote flow around and between adjacent villi. This results largely from folding of the relatively inelastic mucosa during repeated radial and longitudinal muscular contraction, causing chyme to be displaced by periodic crowding and separation of the tips of the relatively rigid villi. Further, micro-rheological studies indicate that such peripheral mixing may extend to the apices of enterocytes owing to discontinuities in the mobile mucus layer that covers the ileal mucosa.

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.