Effects of simulated digestion in vitro on cell wall polysaccharides from kiwifruit (Actinidia spp.)

Cell wall polysaccharides are resistant to digestion and absorption in the human small intestine and are considered to be delivered to the colon in a chemically unaltered state. In this paper, pulp from green and gold kiwifruit was subjected to in vitro upper-intestinal tract digestion and the chemical and physical changes to cell wall polysaccharides (dietary fibre) were investigated. Yields of insoluble fibre decreased slightly with simulated digestion while soluble fibre yields increased. Constituent sugar and glycosyl linkage analysis of the soluble and insoluble fibre fractions revealed that the chemical composition and structure of the non-starch polysaccharides remained largely unchanged. However, the degree of methylesterification of galacturonic acid residues present in the pectin-rich soluble fibre fractions of both fruit decreased with treatment; size-exclusion chromatography detected changes in the molecular weight profiles of these fractions. These changes may affect the physicochemical properties and fermentability of kiwifruit dietary fibre in the large intestine.     

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     

Influence of chemical and physical modification on the bile acid binding capacity of dietary fibre from lupins (Lupinus angustifolius L.)

Bile acid adsorption by dietary fibre in the human intestine is widely considered to be a mechanism for lowering the blood cholesterol level and reducing the risk of colon cancer. In this study, the influence of physical and chemical treatment on the bile acid binding capacity of lupin dietary fibres was determined in vitro. Various methods for modifying dietary fibres were investigated (enzymatic, acid, and alkaline hydrolysis, as well as acetylation). The bile acid binding capacity was measured using an enhanced in vitro digestion model. The native lupin fibre product showed a bile acid binding capacity of 19%, whilst the medication cholestyramine exhibited a binding capacity of almost 100%. Enzymatic and acid hydrolysis caused a significantly increased binding capacity of up to 38%, corroborating the importance of dietary fibre structure, composition, and degree of degradation as determining factors for the bile acid binding capacity. The results of the acetylation experiments support the hypothesis of a hydrophobic linkage between bile acids and dietary fibre. Furthermore, the binding capacity depends on the particle size distribution, and consequently on the particle specific surface area.     

Effects of two contrasting dietary fibres on starch digestion,short‐chain fatty acid production and transit time in rats

Dietary fibres may cause dietary starch to escape digestion in the small intestine and enter the large intestine. If this results from the dietary fibres reducing the gastrointestinal transit time, those dietary fibres that reduce this the most would be expected to cause the most starch to escape digestion. We tested in rats the relative abilities of two contrasting dietary fibres, apple pectin (a soluble dietary fibre) and wheat straw (an insoluble, lignified dietary fibre), to reduce the whole gut transit time and to cause dietary starch to escape digestion. We provided male Wistar rats with a control, modified AIN‐76™ diet containing 20% fat but no dietary fibre, and with this diet containing 10% dietary fibre; the dietary fibre replaced the equivalent weight of starch in the control diet. Both dietary fibres, but particularly wheat straw, reduced the transit time compared with the fibre‐free control diet. Pectin, but not wheat straw, resulted in substantial amounts of starch in the caecal contents. This effect may result from the pectin increasing the viscosity of the digesta or causing it to gel. Large amounts of short‐chain fatty acids were found only in the caeca of rats provided with pectin. © 2000 Society of Chemical Industry     

Polyphenols associated with dietary fibre in wine: A wine Polyphenols gap?

The presence of polyphenolic compounds associated with dietary fibre is a characteristic feature of polyphenol-rich plant foods. It was recently reported that soluble dietary fibre is a common constituent of wine. The objective of this work was to ascertain whether significant amounts of wine polyphenols are associated with dietary fibre. Total phenolics, antioxidant capacity, and HPLC analysis were determined in wines and in corresponding dietary fibre solutions obtained after enzymatic treatments and dialysis. Results showed that 35–60% of total polyphenols in red wine and about 9% in white wine are associated with dietary fibre. These polyphenols are not detected by the usual HPLC analytical techniques and consequently may be ignored in most chemical and biological studies – what we call “the wine polyphenols gap”. Our findings suggest that a significant part of wine polyphenols are not bioaccesible in the human small intestine and reach the colon along with dietary fibre.     

Microbial protein synthesis and flows of nitrogen fractions to the duodenum of dairy cows.

Attempts have been made to increase nutrient availability for milk production by increasing feed intake, optimizing ruminal fermentation, and supplementing nutrients to the diet that will escape ruminal degradation. Energy and N are the nutritional factors that most often limit microbial growth and milk production. Ruminal fermentation and flow of microbial and dietary protein to the small intestine are affected by feed intake and by the amount and source of energy and protein in the diet. Feeding protein and carbohydrate that are not degraded in the rumen increases the quantity of dietary protein that passes to the small intestine but may decrease the quantity of microbial protein that is synthesized in the rumen. This often results in only small differences in the total NAN that passes to the small intestine. Because microbial protein supplies a large quantity of total AA that passes to the small intestine, differences in passage of individual AA often are only slight. Additional research with cows consuming large amounts of feed are needed to identify combinations of feed ingredients that synchronize availabilities of energy and N for optimizing ruminal digestion, microbial protein synthesis, nutrient flow to the small intestine, and milk production and composition.     

Avoparcin and Monensin Effects on Digestive Function in Cows Fed a High Forage Diet

Three non-lactating cows with ruminal, duodenal, and ileal cannulas were used in a 3×3 Latin square design to evaluate the effect of oral avoparcin and monensin on fibre, starch, and nitrogen (N) digestion. Cows were fed three high forage diets; the control diet had no additive, and the others contained 33 mg kg⁻¹ DM of either avoparcin or monensin. Neither additive affected apparent total tract digestibilities of organic matter, fibre, starch or N. Avoparcin and monensin reduced the ruminal breakdown of fibre, starch and dietary N. Efficiency of bacterial N synthesis was unchanged, and passage of bacterial N to the small intestine was not modified. Compared with the control, additives caused a greater proportion of feed starch, N, and total amino acid to be digested in the small intestine than in the rumen. Diets containing avoparcin or monensin increased availability of total essential amino acid in the small intestine compared with that of control diets. Post-ruminal digestion of fibre was greater for diets supplemented with antibiotics, because the cows compensated digestion in the lower forestomach.     

Polyphenol and nutrient release from skin of almonds during simulated human digestion

The bioaccessibility of nutrients and phytochemicals from almond skin has not been previously evaluated. We quantified the release of lipid, protein and polyphenols during simulated human digestion from natural (NS) and blanched (BS) skins, the latter being a by-product of the almond industry. Higher percentages of polyphenols were released from NS compared to BS during in vitro digestion. Most of the limited release of lipid and protein occurred during gastric digestion, with no significant differences between NS and BS. The total dietary fibre content was 45% for NS and 46% for BS, glucose and galacturonic acid being the major sugars present. No changes in dietary fibre composition and distribution of autofluorescent phenolics were observed in the cell walls of almond skin after simulated digestion. In the GI tract, the cell walls may therefore function as a useful source of fermentable fibre with beneficial implications for gut health.     

Dietary fiber. Effect on colon carcinogenesis]

The etiopathogenesis of colon carcinogenesis is supposed to be a two-step process consisting of initiation and promotion. In human nutrition the range of xenobiotics acting possibly as initiators occurs mostly in very low concentrations. Therefore, performing a one-factorial consideration they are not claimed seriously to account for initiation. On the contrary, it can be taken for granted that bile acids exert promoting effects in connection with colon carcinogenesis. All factors influencing the promoting effect of bile acids are able to do so probably due to a decrease of pH and as a result the shift of the two bile acid fractions in favour of the soluble fraction, and/or due to the intensification of shift of bile acid metabolism (7-alpha-dehydroxylase). These processes are indirectly influenced to a large extent by the lipid content of food as a result of cholegenesis induction. The "protective Effect" of dietary fibre in colon carcinogenesis (reduced number of tumour carriers, and/or number of tumors per animal) cannot been interpreted as such. Only a delayed promotion phase could been proven. It can be reached only by plant products (bran, lupin), but not by dietary fibre in general.     

Laminarin in the dietary fibre concept

Dietary fibres consist of edible plant polysaccharides that are resistant to digestion and absorption in the human small intestine but undergo complete or partial fermentation in the colon. Seaweeds, notably Laminaria spp, are particularly rich in polysaccharides resistant to hydrolysis in the upper gastrointestinal tract and are, in consequence, considered as dietary fibres. Most of the carbohydrates from Laminaria spp are thought to be indigestible by humans. The main storage polysaccharide of these algae is laminarin, a β‐polymer of glucose. The aims of this work were, on the one hand, to compare various methods of extraction of laminarin by partial characterisation of the product obtained and, on the other hand, to study the fate of this polysaccharide and its effects in the gastrointestinal tract in order to determine its potential as a dietary fibre in human nutrition. Among four methods tested to extract laminarin, the best appeared to be a hot HCl‐based method. Human digestive enzymes did not hydrolyse laminarin, so this polysaccharide can be considered as a dietary fibre. After ingestion by rats, this polysaccharide was not found in faeces of these animals. It did not increase the intestinal transit and stool output in vivo, but it increased the contractile response of the stomach to acetylcholine in vitro. Copyright © 2004 Society of Chemical Industry     

Dietary carbohydrates: classification by chemistry and physiology

Food carbohydrates consist of mono-, di-, oligo- and polysaccharides, the latter composed of starch and non-starch polysaccharides (NSP). The glycaemic response to both sugars and starches is dependent on the types of sugars present and the form of the starches, and ‘complex carbohydrates’ do not necessarily produce slower or lower glycaemic responses than the sugars. Carbohydrates not absorbed in the small intestine are fermented more or less extensively by the large intestinal microflora. There is a fundamental difference nutritionally between digestible and undigestible (‘unavailable’) carbohydrates. NSP, resistant starch (RS) and oligosaccharides are the main forms of undigestible carbohydrates. Dietary fibre is generally conceived as more or less synonymous with ‘unavailable’ carbohydrates. The nutritional effects of dietary fibre are related to its undigestibility in the small intestine, and to the physical and chemical properties of its constituent polysaccharides. Food structures built of dietary fibre as plant cell-walls, and also of other food components, are increasingly recognized as nutritionally important. Food databases should include as much specific and detailed information as possible on food carbohydrates. For food labelling, carbohydrates have to be divided into a number of nutritionally meaningful classes. A first classification should then aim at differentiating the digestible and undigestible carbohydrates, i.e. dietary fibre.     

Proanthocyanidin metabolites associated with dietary fibre from in vitro colonic fermentation and proanthocyanidin metabolites in human plasma

Proanthocyanidins (PAs) or condensed tannins, a major group of dietary polyphenols, are oligomers and polymers of flavan‐3‐ol and flavan‐3, 4‐diols widely distributed in plant foods. Most literature data on PAs' metabolic fate deal with PAs that can be extracted from the food matrix by aqueous‐organic solvents ( extractable proanthocyanidins). However, there are no data on colonic fermentation of non‐extractable proanthocyanidins (NEPAs), which arrive almost intact to the colon, mostly associated to dietary fibre (DF). The aim of the present work was to examine colonic fermentation of NEPAs associated with DF, using a model of in vitro small intestine digestion and colonic fermentation. Two NEPA‐rich materials obtained from carob pod (Ceratonia siliqua L. proanthocyanidin) and red grapes (grape antioxidant dietary fibre) were used as test samples. The colonic fermentation of these two products released hydroxyphenylacetic acid, hydroxyphenylvaleric acid and two isomers of hydroxyphenylpropionic acid, detected by HPLC‐ESI‐MS/MS. Differences between the two products indicate that DF may enhance the yield of metabolites. In addition, the main NEPA metabolite in human plasma was 3,4‐dihydroxyphenyl acetic acid. The presence in human plasma of the same metabolites as were detected after in vitro colonic fermentation of NEPAs suggests that dietary NEPAs would undergo colonic fermentation releasing absorbable metabolites with potential healthy effects.     

In vitro model to correlate viscosity and bile acid-binding capacity of digested water-soluble and insoluble dietary fibres

Binding and excretion of bile acids in the small intestine by water-soluble and insoluble dietary fibres is one of the main mechanisms for their cholesterol-lowering effects. A model for the determination of the bile acid-binding capacity of dietary fibres was developed. The experimental set-up allowed to correlate the bile acid-binding capacities of different fibres with their viscosities after in vitro digestion. For cellulose, native oat fibre and psyllium fibres clear correlations between viscosity and bile acid-binding capacity could be observed, whereas for water-insoluble lupin fibre such a correlation did not exist. Heat-damaged oat fibre also showed bile acid-binding despite of significantly decreased viscosity. The data demonstrated that bile acid-binding of digested dietary fibres may not be solely based on their viscosity but may be influenced by additional binding forces.     

Resistant Starch: Physiological Roles and Food Applications

A portion of starch and starch products that resist digestion in small intestine has been described as resistant starch. Starch may become resistant to digestion due to several reasons, as it may be physically inaccessible, retrograded, or chemically modified. Resistant starch may be categorized as a functional dietary fiber, as defined by the American Association of Cereal Chemists and Food and Nutrition Board of the Institute of Medicine of the National Academics. Resistant starch appears to confer considerable health benefits like reduction in risk of colon cancer, hemorrhoids, diverticulosis, constipation, increased fecal bulking, modulation of blood glucose level, and blood cholesterol level as well as play a prebiotic role. Resistant starch has low water holding capacity, small particle size, and bland flavor. Incorporation of resistant starches in baked products, pasta products and beverages imparts improved textural properties and health benefits. Resistant starches are being examined for both their potential health benefits as well as functional properties to produce high quality foods. However, the results and findings of different studies are hampered by differences in experiment design, and differences in sources, types, and doses of resistant starch.     

Resistant Starch: Physiological Roles and Food Applications

A portion of starch and starch products that resist digestion in small intestine has been described as resistant starch. Starch may become resistant to digestion due to several reasons, as it may be physically inaccessible, retrograded, or chemically modified. Resistant starch may be categorized as a functional dietary fiber, as defined by the American Association of Cereal Chemists and Food and Nutrition Board of the Institute of Medicine of the National Academics. Resistant starch appears to confer considerable health benefits like reduction in risk of colon cancer, hemorrhoids, diverticulosis, constipation, increased fecal bulking, modulation of blood glucose level, and blood cholesterol level as well as play a prebiotic role. Resistant starch has low water holding capacity, small particle size, and bland flavor. Incorporation of resistant starches in baked products, pasta products and beverages imparts improved textural properties and health benefits. Resistant starches are being examined for both their potential health benefits as well as functional properties to produce high quality foods. However, the results and findings of different studies are hampered by differences in experiment design, and differences in sources, types, and doses of resistant starch.     

Use of brush border membrane vesicles to simulate the human intestinal digestion

The intestine presides over a series of vital functions in the human body, among which the digestion/absorption of nutrients. Despite their major digestion role, the impact of the enzymes of the luminal intestinal surface on food components has been considered in relatively few experiments of simulated gastrointestinal digestion. In contrast, the identification of proteolitically stable peptides which survived digestion in multiphasal models that also included a step with small intestinal brush border membrane (BBM) peptidases has provided physiologically consistent results. Herein, we critically review the use of BBM enzymes to simulate the intestinal digestion of dietary polypeptides. Addressing the controversial issue of the in vitro–in vivo correspondence of the digestion models, the review emphasizes the need to establish consensus protocols to simulate the intestinal step, for instance using the BBM hydrolases at least in a selected number of cases. The factors that have limited the development of relevant models of intestinal degradation are discussed together with hints to possible alternatives, forthcoming approaches and future perspectives to reproduce the physiopathology of the human small intestine.     

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     

Whole grains — impact of consuming whole grains on physiological effects of dietary fiber and starch

Much of the present research on the physiological effects of dietary fiber and starch has been done on sources isolated from the parent material, and it is not clear whether they have the same effects if fed in the intact or whole grain. For dietary fiber, physiological effect depends on extent of fermentation in the large intestine, and this is influenced by chemical composition, solubility, physical form, and presence of lignin or other compounds. All of these factors are altered by isolation of a fiber source from the whole grain, and hence effects of eating fiber vary. Similarly, physical form and presence in the whole grain will affect digestibility of starch in the small intestine, which in turn influences the glycemic response and colonic effects determined by the extent of malabsorption and entry into the colon. Starch that enters the colon is fermented and produces short‐chain fatty acids, particularly butyrate, which is necessary to maintain a healthy mucosa. Hence, their presence within the whole grain may have important implications for health for both dietary fiber and starch. Evidence indicates that such effects are beneficial and that whole‐grain consumption should be encouraged.     

Nutrient digestibility and endogenous protein losses in the foregut and small intestine of weaned dairy calves fed calf starters with conventional or enzyme-treated soybean meal

The aims of this experiment were (1) to compare the effects of a soybean meal with an enzymatic treatment (ESBM) to reduce the concentration of antinutritional factors versus a standard soybean meal (SBM) on foregut and small intestine digestion in weaned dairy calves and (2) to estimate the endogenous losses of crude protein (CP) in the small intestine. Our hypothesis was that a diet containing ESBM instead of SBM would improve ruminal and small intestine digestion and absorption of nutrients. A T-cannula was placed in the duodenum, and a second T-cannula was installed in the distal ileum of 12 Holstein calves at approximately 3 wk of age. Calves were weaned on d 42, and on d 50 they were assigned randomly to a quadruplicated 3 × 3 Latin square with 10-d periods. Digesta samples were collected on d 7 and 8 from the ileum and d 9 and 10 from the duodenum. The diets were fed for ad libitum intake and consisted of a calf starter (CS) of 20% CP with SBM as the main source of protein (CTRL), and an isonitrogenous CS with an ESBM instead of SBM (ENZT). A third diet with a low content of CP (10%) and no soy protein was fed to estimate endogenous N losses and digestibilities of test ingredients. Flows and digestibilities of nutrients were compared between CTRL and ENZT and their test ingredients (SBM vs. ESBM, respectively). Duodenal net flows of CP and total AA as well as ruminal microbial protein synthesis per kilogram of digested CP were greater, and flow of nonprotein N and CP true (corrected by endogenous and microbial flows) foregut digestibility were lower with ENZT than CTRL. The apparent small intestine digestibilities of CP and total AA were greater for ESBM than SBM, but there were no differences between the CTRL and ENZT diets. We observed no differences in digestibilities at the duodenum or ileum of starch or NDF, but true small intestine digestibilities of CP and all AA were greater with ENZT than CTRL. Total endogenous protein losses in the small intestine estimated from calves fed the low-CP with no soy protein diet were 37 ± 1.5 g of CP and 29 ± 1.4 g of AA/kg of DMI. These values may be considered the basal endogenous losses as they are similar to values obtained with the regression method, which estimates N losses when dietary N is null. Our results indicated that the inclusion of an ESBM improved the efficiency of ruminal microbial protein synthesis per digested kilogram of organic matter and CP, and increased CP and AA absorption in the small intestine despite a greater proportion of undigested dietary protein entering the duodenum.     

膳食营养剂对灰褐牛肝菌中镉的生物可给性及其健康风险的影响

聚焦灰褐牛肝菌(Boletus griseus)富镉(Cd)问题,调研了云南3个地区B. griseus样本中的总Cd含量,选取了高、中、低3种不同Cd含量B. griseus样本,建立了一种更易实现、更易量化的体外全仿生消化方法,评价了B. griseus中镉的生物可给性(Cd-BAc),研究了单宁酸、CaCl₂、原花青素、葡萄糖酸锌钙、红毛丹果皮多酚5种膳食营养成分对Cd-BAc的影响,并以此为基础评价了B. griseus中Cd的食用健康风险。结果表明,采集的53个B. griseus样本均具有较高的总Cd含量,在胃部的Cd-BAc为55.30%~59.36%,但是小肠的弱碱近中性环境显著降低了B.griseus中Cd的溶出,Cd-BAc为39.59%~52.86%,大肠菌群发酵进一步降低Cd-BAc至21.41%~25.28%。5种膳食营养剂在胃部对Cd-BAc影响不大,在小肠部和大肠菌群发酵中,均显著降低了Cd-BAc,CaCl₂效果最为显著。以B. griseus中Cd总量计,摄食中镉、高镉含量的B. griseus,Cd对人体的风险熵为2.98和5.13;综合考虑Cd-BAc以及5种膳食营养剂的影响,其风险熵可降低至0~0.37。研究结果表明,B. griseus中Cd的食用健康风险很高,膳食营养剂可通过降低肠道Cd-BAc而调控其对人体的健康风险,因此,膳食营养剂可能是控制高镉食品健康风险的一种有效策略,但是该策略的有效性需要进一步的体内实验验证。