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.     

Lactose--a potential dietary fiber. The regulation of its microecological effect in the intestinal tract. 1. Problems, state of knowledge and methods]

Food components of different chemical structure which attain the colon without being attacked by digestion and absorption during their transit through the small intestine are defined as dietary fibre. In the colon they serve as energy or nutrient source for the intestinal microflora or are excreted without change. Not only chemical structure is decisive when a food component has to be assigned to either nutrients or dietary fibre: Substances resisting small intestine digestion due to the lack of corresponding catabolizing enzymes in man are supposed to be "obligate" dietary fibre. "Potential" dietary fibre are nutrients which are only partially digested in the small intestine. Lactose--the main carbohydrate of milk--represents a typical potential dietary fibre. The present paper investigates the factors being responsible for both the degree of lactose utilization in the small intestine and its efficiency in the colon.     

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.     

Effects of dietary broccoli fibre and corn oil on serum lipids, faecal bile acid excretion and hepatic gene expression in rats

To determine the effects of broccoli fibre and corn oil on lipid metabolism, male Sprague-Dawley rats were fed diets containing high (30%) or low (5%) corn oil, in combination with either 7.5% broccoli fibre or cellulose, for 4 months. High corn oil groups had significantly lower serum cholesterol and triglycerides than had low corn oil groups (p < 0.001). Broccoli fibre also lowered serum cholesterol and triglyceride levels compared to cellulose fibre. Faecal bile acid concentrations were higher in high corn oil-fed rats than in low corn oil-fed rats, with broccoli fibre inclusion in high corn oil diets resulting in higher faecal bile acid concentrations. Regardless of corn oil level, broccoli fibre supplementation in the diet resulted in an increase (p = 0.018) in hepatic cytochrome P450, family 7A1 (CYP7A1) expression. High corn oil feeding resulted in reduced expression of fatty acid synthase (FAS) and increased expression of carnitine palmitoyl transferase 1a (CPT1a) and 3-hydroxy-3-methyl-coenzyme A reductase (HMGCR) (p < 0.05). Our findings suggest that high dietary corn oil and broccoli fibre have beneficial effects on lipid metabolism. Corn oil lipid-lowering effects may be due to alteration of hepatic expression of genes involved in lipid synthesis and increased rate of cholesterol catabolism to bile acids. Broccoli fibre may also act via its physical properties to reduce enterohepatic bile acid recycling and intestinal lipid absorption, and increase luminal binding of bile acids, resulting in increased faecal bile acid excretion.     

Interactions between dietary fibre-rich preparations and glycoconjugated bile acids in vitro

Binding in small intestine and excretion of bile acids constitute a major hypocholesterolemic pathway. Interactions between different types of commercial and laboratory-made dietary fibres and glycoconjugated bile acids were investigated in vitro at pH 5.0 and 6.5. The interactions were greater at the lower pH and with dihydroxy-bile acids. Digested cereal products (barley, oat, rye and wheat flour; oat bran), alcohol-insoluble substances from apples, strawberries, rowan berries, carrots, white cabbage, red beets and sugar beet pulp, as well as arabinoxylan, bound 1.21–1.77 μmol bile acids/100 mg of preparation at pH 5.0. Novelose bound approximately 0.65 μmol bile acids/100 mg. Carob fibre had the highest binding capacity (1.83–1.96 μmol bile acids/100 mg) whereas cellulose had no effect. Besides the source and chemical composition, the bile acid binding correlated especially well with the presence of three-dimensional cell wall structures of the tested preparations but less well with the proportions of soluble and insoluble dietary fibre.     

Role of the conjugated linoleic acid in the prevention of cancer

There are multiple lines of evidence that a variety of natural fatty acids are effective in health promotion. Among these fatty acids, conjugated linoleic acid (CLA)--a collective term referring to a mixture of positional and geometric isomers of linoleic acid (LA, cis-9, cis-12-octadecadienoic acid)--is currently under intensive investigation due to its health-promotion potential. The antitumor activity of CLA is of special interest, since it shows inhibitory effects against multistage carcinogenesis at relatively low dietary levels. Many studies using in vivo and in vitro models have shown that CLA suppresses the development of multistage carcinogenesis at different sites. The research to date on CLA has provided a vast amount of information about the mechanism on how CLA functions in the prevention of cancer. This article discusses characteristics of CLA in the prevention of cancer in both in vivo and in vitro studies and the possible underlying chemoprevention mechanisms.     

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.     

Comparative study of colorectal health related compounds in different types of bread: Analysis of bread samples pre and post digestion in a batch fermentation model of the human intestine

Seven different types of wheat and rye bread were analysed for colorectal health related compounds, pre and post digestion, in batch fermentation model of the human intestine. Pre digestion, higher amounts of colorectal health-related dietary fibre compounds (soluble/insoluble/total dietary fibre, arabinoxylans, β-glucans) and phytochemicals (mono-/di-phenolic acids, phytic acid, hydroxymethylfurfural) were detected in wholemeal than in refined flour types of bread, as well as in rye flour types than in wheat flour types of bread. Post digestion, faecal bacterial metabolites of colorectal health promoting (acetate/propionate/butyrate, lactate, free mono-/di-phenolic acids) and impairing (amino metabolites, bile acid metabolites) activities were found in fermentation supernatants of bread samples. All types of bread positively affected faecal bacterial metabolism; among the different types of bread, the highest stimulation of organic acid production (acetate/propionate/butyrate, lactate) and the lowest detrimental bacterial enzyme activities (β-glucuronidase, urease) were detected for wheat flour bread, whereas the strongest retardation of bacterial bile acid degradation and the strongest stimulation of phenolic acid metabolite release (phenylpropionic/phenylpropenoic acid derivatives) were induced by wholemeal rye bread. This study for the first time presents a qualitative and quantitative overview over the broad spectrum of colorectal health related compounds in high- and low-fibre types of bread, pre and post in vitro digestion, and highlights the significance of bread for the preventive nutritional intervention of colorectal cancer.     

In vitro binding of bile acids by spinach, kale, brussels sprouts, broccoli, mustard greens, green bell pepper, cabbage and collards

The in vitro binding of bile acids by spinach (Spinacia oleracea), kale (Brassica oleracea acephala), Brussels sprouts (Brassica oleracea gemmifera), broccoli (Brassica oleracea italica), mustard greens (Brassica juncea), green bell peppers (Capsicum annuum), cabbage (Brassica oleracea capitala) and collards (Brassica oleracea acephala) was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted testing various fresh raw green vegetables on an equal dry matter basis. Considering cholestyramine (bile acid binding, cholesterol lowering drug) as 100% bound, the relative in vitro bile acid binding of various vegetables tested on equal dry matter and total dietary fibre basis was 2–9% and 6–32%, respectively. Bile acid binding for spinach, kale and brussels sprouts was significantly higher than for broccoli and mustard greens. For broccoli and mustard greens binding values were significantly higher those for cabbage, bell pepper and collards. These results point to the health promoting potential of spinach = kale = brussels sprouts > broccoli = mustard greens > cabbage =  green bell peppers =  collards, as indicated by their bile acid binding on dry matter basis.     

Resistant starch and “the butyrate revolution”

Early epidemiological studies indicated that populations that consume a high proportion of non-starch polysaccharide (NSP) dietary fibre (DF) in their daily diet suffer less from gastrointestinal diseases, in particular colorectal cancers, than populations that consume diets that are high in fat and protein but low in NSP fibre. In this respect, diet, by increasing the amount of vegetables and NSP DF's, has been suggested to contribute as much as 25–35% to risk reduction for colorectal cancer. A reduction of fat intake may further reduce the risk by 15–25%. Based on these observations, DF's and substances that are part of the fibre complex such as antioxidants, flavonoids, sulphur containing compounds and folate have been proposed as potentially protective agents against colon cancer. However, results from controlled prospective studies in which beta-carotene and vitamin E or isolated dietary fibres were given to high risk groups showed disappointing results. There are recent indications that the regular consumption of certain subclasses of highly fermentable dietary fibre sources result in gut associated immune and flora modulation as well as a significant production of short chain fatty acids. In vitro studies as well as animal studies indicate that in particular propionate and butyrate have the potential to support the maintenance of a healthy gut and to reduce risk factors that are involved in the development of gut inflammation as well as colorectal cancer. A suggestion put forward is that beneficial effects may be obtained in particular by the consumption of resistant starch (RS) because of the high yield of butyrate and propionate when fermented. These SCFA are the prime substrates for the energy metabolism in the colonocyte and they act as growth factors to the healthy epithelium. In normal cells butyrate has been shown to induce proliferation at the crypt base, enhancing a healthy tissue turnover and maintenance. In inflamed mucosa butyrate stimulates the regeneration of the diseased lining of the gut. In neoplastic cells butyrate inhibits proliferation at the crypt surface, the site of potential tumour development. Moreover, models of experimental carcinogenesis in animals have shown the potential to modify a number of metabolic actions and steps in the cell cycle in a way that early events in the cascade of cancer development may be counteracted while stages of progression may be slowed down. The present review highlights a number of these aspects and describes the metabolic and functional properties of RS and butyrate.     

Selective in vivo effect of chitosan on fatty acid,neutral sterol and bile acid excretion: A longitudinal study

Chitosan, a deacetylated form of chitin, is a dietary fibre known for its hypolipidemic properties, which are mainly attributed to its unique cationic characteristics. We studied the selective in vivo effect of chitosan on fat excretion in order to elucidate its hypolipidemic mechanism. A 4-week longitudinal study was conducted in guinea pigs and the effect of chitosan on fat-absorption was compared to that of a soluble fibre: digestion-resistant maltodextrin. Animals were fed with high-fat isocaloric diets containing 12/100 g of cellulose, digestion-resistant maltodextrin or chitosan. Subsequently, the excretion of fatty acids, neutral sterols and bile acids was determined. Chitosan selectively reduced fat absorption in comparison to digestion-resistant maltodextrin. The excretion of lauric, myristic and palmitic fatty acids of animals fed with chitosan was more than 10-, 5- and 2-fold higher, respectively, than in the cellulose group, whereas stearic acid excretion was not significantly altered. Oleic, linoleic and α-linolenic acid excretion were also significantly higher (P < 0.001). The n−6/n−3 ratio in faeces of the chitosan group was 23.68, compared to 13.95 in the cellulose group. Total neutral sterol excretion was increased by both dietary fibres, whereas bile acid excretion was only increased by chitosan. Nevertheless, chitosan inhibited the intestinal bioconversion of cholesterol and primary bile acids to secondary metabolites. Hence, these results reveal that chitosan and digestion resistant maltodextrin exert their hypolipidemic activity by different mechanisms.     

Dietary fibres as "prebiotics": implications for colorectal cancer

A "prebiotic" is a nondigestible food ingredient whose beneficial effects on the host result from the selective stimulation of growth and/or activity of members of the bacterial community that inhabits the human bowel (the gut microbiota). Although much of the prebiotic literature focuses on nondigestible oligosaccharides, such as oligofructose, most dietary fibres that are fermentable carbohydrates could be considered as prebiotics. Early studies suggested that colonic bacteria were risk factors for colon cancer. However, altering the composition or metabolic activity of the bowel microbiota through the use of dietary fibre might be important in reducing the prevalence of colorectal cancer. Mechanisms for beneficial effects of prebiotics might include changing the activity of exogenous carcinogens through modulating metabolic activation and/or detoxification, or stimulating the production of the short-chain fatty acid, butyrate. However, modern analytical techniques suggest that an important consequence of a modified bacterial community could be a change in the expression not only of a range of different bacterial genes in bowel contents, but also in the bowel mucosa of the host. Analogous with observations with probiotics, the stimulation of cytokines and modification of immune responses could be important in producing beneficial effects. Compared with transitory effects of probiotics, the prebiotic action of fermentable carbohydrates potentially provide the opportunity for sustainable modulation of activity of the gut microbiota. However, their mechanisms of action in humans are speculative, and research aimed at providing an integrated view of the gut microbiota and dietary fibre nutrition of humans needs to be developed.     

Mango peel dietary fibre: Composition and associated bound phenolics

Dietary fibre and polyphenols are widely used as functional food ingredients. In this study, carbohydrate composition and bound phenolics in dietary fibre of mango peels were determined. Total dietary fibre content was in the range of 40.6–72.5%. Galactose, glucose and arabinose were the major neutral sugars in insoluble and soluble dietary fibres. Bound polyphenolic and flavonoid contents were in the range of 8.1–29.5 and 0.101–0.392 mg/g, respectively, and were found to be more in ripe peel than in raw peel. Gallic, protocatechuic and syringic acids were the bound phenolic acids, and kaempferol and quercetin were the major flavonoids of the peels. Ferulic acid was identified only in dietary fibre of Raspuri peels. Thus, the studies indicated the presence of significant amount of bound phenolics in dietary fibre, which adds additional health benefits of antioxidant properties of mango peel, which can be used in functional foods.     

In vitro binding of bile acids by okra,beets, asparagus,eggplant, turnips,green beans,carrots, and cauliflower

The in vitro binding of bile acids by okra (Abelmoschus esculentus), beets (Beta vulgaris), asparagus (Asparagus officinalis), eggplant (Solanum malongena), turnips (Brassica rapa rapifera), green beans (Phaseolus vulgaris), carrots (Daucus carota), and cauliflower (Brassica oleracea botrytis) was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted, testing various fresh raw vegetables on an equal dry matter basis. Considering cholestyramine (bile acid-binding, cholesterol-lowering drug) as 100% bound, the relative in vitro bile acid binding on dry matter (DM) and total dietary fibre (TDF) basis was 1–16% and 2–54%, respectively. Bile acid binding for okra was significantly higher than for all the other vegetables tested. For beets, binding values were significantly higher than for asparagus. Binding values for asparagus were significantly higher than for eggplant, turnips, beans green, carrots and cauliflower. These results point to the health promoting potential of okra > beets > asparagus > eggplant = turnips = green beans = carrots = cauliflower, as indicated by their bile acid binding, on a dry matter basis.     

An investigation of the experimental conditions which could affect water-holding capacity of dietary fibre

The water-holding capacity (WHC) of various sources of vegetable and cereal dietary fibre has been measured under different experimental conditions. WHC was measured by centrifugation and filtration. The results obtained suggest that prolonged soaking has no effect on WHC. Fibre agitation, the presence of buffer (pH 7.5), and the presence of bile salt (deoxycholate) also had no effect on WHC, except for never-dried potato fibre (NDPF) (fresh fibre concentrate). WHC, however, does vary with the method of measurement and the WHC determined by centrifugation was greater than that determined by filtration. The differences in WHC between NDPF and dried potato fibre are not due to gross chemical differences in the fibre. The conditions used for the preparation of dietary fibre and the measurement of its WHC, therefore, must be carefully controlled before the role of fibre in the diet can be better understood.     

Chemopreventive Potential of Wild Lowbush Blueberry Fruits in Multiple Stages of Carcinogenesis

ABSTRACT: Wild lowbush blueberry fruit extract was fractionated using vacuum chromatography and analyzed for chemopreventive potential using bioassays that test the ability of compounds to inhibit the initiation, promotion, and progression stages of carcinogenesis. A fraction containing phytosterols was active against the initiation stage (quinone reductase assay). However, more polar compounds were inhibitors of later stages of carcinogenesis; a fraction containing flavan-3-ols and fractions containing mainly anthocyanins, phenolic acids, flavan-3-ols, and some proanthocyanidin dimers demonstrated activity against the promotion stage (cyclooxygenase and ornithine decarboxylase assays, respectively), and a proanthocyanidin-rich fraction demonstrated antiproliferation activity (inhibition of cancerous murine hepatocyte proliferation is associated with the progression stage). These results indicate that lowbush blueberries contain a range of compounds that have bioactivity against multiple stages of carcinogenesis, and different types of phenolic compounds are active at different stages.     

In vitro binding of bile acids by bananas,peaches, pineapple,grapes, pears,apricots and nectarines

The in vitro binding of bile acids by bananas (Musa × paradisiaca), peaches (Prunus persica), pineapple (Ananus comosus), grapes (Vitis spp.), pears (Pyrus communis), apricots (Prunus armeniaca) and nectarines (Prunus persica, nectarina) was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted, testing various fresh fruits on an equal dry matter basis. Considering cholestyramine (bile acid binding, cholesterol lowering drug) as 100% bound, the relative in vitro bile acid binding percentages on dry matter (DM), total dietary fibre and total polysaccharides basis were 2–9%, 15–101% and 10–101%, respectively. Bile acid binding, on a DM basis, for bananas was significantly (P ? 0.05) higher and that for nectarines significantly lower than those for peaches, pineapple, grapes, pears and apricots. The bile acid bindings for peaches and pineapple were similar and significantly higher than those for grapes, pears and apricots. Binding values for grapes and pears were significantly higher than apricots. These results point to the relative health promoting potential of bananas > peaches = pineapple > grapes = pears > apricots > nectarines, as indicated by their bile acid binding on a DM basis. The variability in bile acid binding between the fruits tested maybe related to their phytonutrients, antioxidants, polyphenols, flavonoids (anthocyanins, flavonols, and proanthocyanidins), structure, hydrophobicity of undigested fractions, anionic or cationic nature of the metabolites produced during digestion or their interaction with active binding sites. Animal studies are planned to validate in vitro bile acid binding of fruits, observed herein, to their healthful potential, atherosclerosis amelioration and cancer prevention.     

High dietary fibre powders from orange and lime peels: associated polyphenols and antioxidant capacity

High dietary fibre powders from Valencia orange and Persa lime peels were prepared and their dietary fibre composition and antioxidant capacity studied. Fibres from both peels had a high total dietary fibre content (61–69%) with an appreciable amount of soluble fibre (19–22%). The concentration of antioxidant [AA₅₀] required to achieve a 50% inhibition of oxidation of linoleic acid at 40°C was measured using the ferric-thiocyanate method. The higher the [AA₅₀], the lower the antioxidant capacity. Lime peel fibre [AA₅₀] was half the value of DL--tocopherol and 23 times lower than orange peel fibre; the [AA₅₀] of commercial butylated hydroxyanisole (BHA) was half the value of lime fibre. HPLC analyses of the polyphenols extracted from orange and lime peels fibres showed the presence of caffeic and ferulic acids, as well as naringin, hesperidin and myricetin in both fruit fibres. The different antioxidant power of these fibres could be in part explained by the presence in lime peel fibre of ellagic acid, quercetin and kaempferol which are strong antioxidant polyphenols.     

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.     

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.