The therapeutic value of specific fibres is partly dependent on their fermentation characteristics. Some fibres are rapidly degraded with the generation of gases that induce symptoms in patients with irritable bowel syndrome (IBS), while more slowly or non-fermentable fibres may be more suitable. More work is needed to profile a comprehensive range of fibres to determine suitability for IBS. Using a rapid in vitro fermentation model, gas production and metabolite profiles of a range of established and novel fibres were compared. Fibre substrates (n 15) were added to faecal slurries from three healthy donors for 4 h with gas production measured using real-time headspace sampling. Concentrations of SCFA and ammonia were analysed using GC and enzymatic assay, respectively. Gas production followed three patterns: rapid (≥60 ml/g over 4 h) for fructans, carrot fibre and maize-derived xylo-oligosaccharide (XOS); mild (30–60 ml/g) for partially hydrolysed guar gum, almond shell-derived XOS and one type of high-amylose resistant starch 2 (RS2) and minimal (no differences with blank controls) for methylcellulose, another high-amylose RS2, acetylated or butyrylated RS2, RS4, acacia gum and sugarcane bagasse. Gas production correlated positively with total SCFA (r 0·80, P < 0·001) and negatively with ammonia concentrations (r –0·68, P < 0·001). Proportions of specific SCFA varied: fermentation of carrot fibre, XOS and acetylated RS2 favoured acetate, while fructans favoured butyrate. Gas production and metabolite profiles differed between fibre types and within fibre classes over a physiologically relevant 4-h time course. Several fibres resisted rapid fermentation and may be candidates for clinical trials in IBS patients.

This study characterised the in vitro ileal fermentability of different substrates in the growing pig, adopted as an animal model for the adult human, and compared in vitro ileal and caecal fermentation in the pig. Substrates (arabinogalactan (AG), cellulose, fructo-oligosaccharide (FOS), inulin, mucin, citrus pectin and resistant starch) were fermented in vitro (ileal 2 h and caecal 24 h) with an ileal or caecal inoculum prepared from ileal or caecal digesta collected from growing pigs (n 5) fed a human-type diet for 15 d. The organic matter (OM) fermentability and production of organic acids were determined. In general, there was considerable in vitro ileal fermentation of fibre, and the substrates differed (P < 0·001) for both in vitro ileal and caecal OM fermentability and for organic acid production. Pectin had the greatest in vitro ileal OM fermentability (26 %) followed by AG, FOS and resistant starch (15 % on average), and cellulose, inulin and mucin (3 % on average). The fermentation of FOS, inulin and mucin was greater for in vitro caecal fermentation compared with the ileal counterpart (P ≤ 0·05). In general, the organic acid production was higher for in vitro caecal fermentation (P ≤ 0·05). For instance, the in vitro ileal acetic acid production represented 4–46 % of in vitro caecal production. Energy from fibre fermentation of 0·6–11 kJ/g substrate fermented could be expected in the ileum of the pig. In conclusion, substrates are fermented in both the ileum and caecum. The degree of fermentation varies among substrates, especially for in vitro ileal fermentation.

Animal studies indicate that the composition of gut microbiota may be involved in the progression of insulin resistance to type 2 diabetes. Probiotics and/or prebiotics could be a promising approach to improve insulin sensitivity by favourably modifying the composition of the gut microbial community, reducing intestinal endotoxin concentrations and decreasing energy harvest. The aim of the present review was to investigate the effects of probiotics, prebiotics and synbiotics (a combination of probiotics and prebiotics) on insulin resistance in human clinical trials and to discuss the potential mechanisms whereby probiotics and prebiotics improve glucose metabolism. The anti-diabetic effects of probiotics include reducing pro-inflammatory cytokines via a NF-κB pathway, reduced intestinal permeability, and lowered oxidative stress. SCFA play a key role in glucose homeostasis through multiple potential mechanisms of action. Activation of G-protein-coupled receptors on L-cells by SCFA promotes the release of glucagon-like peptide-1 and peptide YY resulting in increased insulin and decreased glucagon secretion, and suppressed appetite. SCFA can decrease intestinal permeability and decrease circulating endotoxins, lowering inflammation and oxidative stress. SCFA may also have anti-lipolytic activities in adipocytes and improve insulin sensitivity via GLUT4 through the up-regulation of 5'-AMP-activated protein kinase signalling in muscle and liver tissues. Resistant starch and synbiotics appear to have favourable anti-diabetic effects. However, there are few human interventions. Further well-designed human clinical studies are required to develop recommendations for the prevention of type 2 diabetes with pro- and prebiotics.

The inhibition by 1,5-anhydro-d-glucitol (1,5-AG) was determined on disaccharidases of rats and humans. Then, the metabolism and fate of 1,5-AG was investigated in rats and humans. Although 1,5-AG inhibited about 50 % of sucrase activity in rat small intestine, the inhibition was less than half of d-sorbose. 1,5-AG strongly inhibited trehalase and lactase, whereas d-sorbose inhibited them very weakly. 1,5-AG noncompetitively inhibited sucrase. The inhibition of 1,5-AG on sucrase and maltase was similar between humans and rats. 1,5-AG in serum increased 30 min after oral administration of 1,5-AG (600 mg) in rats, and mostly 100 % of 1,5-AG was excreted into the urine 24 h after administration. 1,5-AG in serum showed a peak 30 min after ingestion of 1,5-AG (20 g) by healthy subjects, and decreased gradually over 180 min. About 60 % of 1,5-AG was excreted into the urine for 9 h following ingestion. Hydrogen was scarcely excreted in both rats and humans 24 h after administration of 1,5-AG. Furthermore, 1,5-AG significantly suppressed the blood glucose elevation, and hydrogen excretion was increased following the simultaneous ingestion of sucrose and 1,5-AG in healthy subjects. 1,5-AG also significantly suppressed the blood glucose elevation following the simultaneous ingestion of glucose and 1,5-AG; however, hydrogen excretion was negligible. The available energy of 1,5-AG, which is absorbed readily from the small intestine and excreted quickly into the urine, is 0 kJ/g (0 kcal/g). Furthermore, 1,5-AG might suppress the blood glucose elevation through the inhibition of sucrase, as well as intestinal glucose absorption.

The present study aimed to evaluate the inter-individual variability in fermentation of standard fibrous substrates by faecal inocula from ten healthy adult female cats. Substrates were citrus pectin (CP), fructo-oligosaccharides (FOS), guar gum (GG), sugar beet pulp (SBP) and wheat middlings (WM). Each substrate was incubated with faecal inoculum from each cat. Gas production was measured continuously during the 48 h incubation and SCFA and organic matter disappearance (only SBP and WM) after incubation. Out of ten cats, nine produced faeces on the days of inoculum preparation. The substrates contrasted in terms of fermentation parameters measured. The inter-individual variability was in general lower for the more simple and pure substrates (CP, FOS, GG) than for the more complex substrates containing mixtures of fibres (SBP, WM). Furthermore, for total SCFA and gas produced, inter-individual variability was lower than for proportions of butyrate and of branched-chain fatty acids and for the parameters of gas production kinetics. It is concluded that the variability in in vitro fermentation parameters is associated with the complexity of fibrous substrates. The presented data are instrumental for the calculation of number of faecal donors required for precise in vitro characterisation of the fermentability of dietary fibres. In addition, the number of faecal donors should be adjusted to the specific fermentation parameter(s) of interest.

To gain knowledge on the precision of an in vitro method for characterisation of the fermentability of dietary fibres, this study aimed to evaluate the repeatability and reproducibility of such a method. Substrates used were citrus pectin (CP), fructo-oligosaccharides (FOS), guar gum (GG), sugar beet pulp (SBP) and wheat middlings (WM). Each substrate was incubated with faecal inoculum from five cats with three replicates for each substrate–cat combination. Gas production was measured continuously during the 48 h incubation and SCFA and organic matter disappearance (only SBP and WM) were determined after incubation. Four consecutive runs were performed. The within-run variability (repeatability) was generally lower for the more simple and pure substrates (CP, FOS, GG) than for the more complex substrates containing mixtures of fibres (SBP, WM). Replicates showed high variability, in particular for SCFA profiles and parameters of gas production kinetics. The between-run CV (reproducibility) for the measured parameters were, in general, below 10 % for CP, FOS and GG and higher values were obtained for SBP and WM. It is concluded that for precise dietary fibre characterisation, the number of replicates should be multiple and adjusted according to the variability of the parameters of interest and the complexity of fibres. The method yielded reproducible results with some variation in absolute values obtained, which may have an impact on the significance level of the differences among substrates.

Resistant glucan (RG) and hydrogenated resistant glucan (HRG) are newly developed non-digestible carbohydrate materials that decrease lifestyle-related diseases. The bioavailability of RG and HRG was investigated by in vitro experiments using human and rat small intestinal enzymes and by in vivo experiments using rats in the present study. Oligosaccharides, which are minor components of RG and HRG, were hydrolysed slightly by small intestinal enzymes of humans and rats, and the hydrolysing activity was slightly higher in rats than in humans. The amount of glucose released from HRG was greater than that from RG. However, the high-molecular-weight carbohydrates of the main components were hardly hydrolysed. Furthermore, neither RG nor HRG inhibited disaccharidase activity. When rats were raised on a diet containing 5 % of RG, HRG, resistant maltodextrin or fructo-oligosaccharide (FOS) for 4 weeks, all rats developed loose stools and did not recover during the experiment, except for the FOS group. Body weight gain was normal in all groups and was not significantly different compared with the control group. Caecal tissue and content weights were significantly increased by feeding RG or HRG, although other organ and tissue weights were not significantly different among the groups. In conclusion, RG and HRG consist of small amounts of glucose and digestible and non-digestible oligosaccharides, and large amounts of glucose polymers, which were hardly hydrolysed by α-amylase and small intestinal enzymes. RG and HRG, which were developed newly as dietary fibre materials, had no harmful effects on the growth and development of rats.

The fruit of the date palm (Phoenix dactylifera L.) is a rich source of dietary fibre and polyphenols. We have investigated gut bacterial changes induced by the whole date fruit extract (digested date extract; DDE) and its polyphenol-rich extract (date polyphenol extract; DPE) using faecal, pH-controlled, mixed batch cultures mimicking the distal part of the human large intestine, and utilising an array of microbial group-specific 16S rRNA oligonucleotide probes. Fluorescence microscopic enumeration indicated that there was a significant increase in the growth of bifidobacteria in response to both treatments, whilst whole dates also increased bacteroides at 24 h and the total bacterial counts at later fermentation time points when compared with DPE alone. Bacterial metabolism of whole date fruit led to the production of SCFA, with acetate significantly increasing following bacterial incubation with DDE. In addition, the production of flavonoid aglycones (myricetin, luteolin, quercetin and apigenin) and the anthocyanidin petunidin in less than 1 h was also observed. Lastly, the potential of DDE, DPE and metabolites to inhibit Caco-2 cell growth was investigated, indicating that both were capable of potentially acting as antiproliferative agents in vitro, following a 48 h exposure. This potential to inhibit growth was reduced following fermentation. Together these data suggest that consumption of date fruits may enhance colon health by increasing beneficial bacterial growth and inhibiting the proliferation of colon cancer cells. This is an early suggestion that date intake by humans may aid in the maintenance of bowel health and even the reduction of colorectal cancer development.

The present study was conducted to investigate the effects of dietary fructo-oligosaccharide (FOS) (0, 1, 2 and 3 %) supplementation on the growth performance, haemato-immunological parameters, cultivable autochthonous (non-adherent) intestinal microbiota and stress resistance of common carp (Cyprinus carpio) fry (3·23 (sem 0·14) g). These parameters were measured after feeding the carp fry with the experimental diets for 7 weeks. Dietary FOS supplementation had no significant effects on the growth performance and food intake of carp fry compared with the control treatment. It also had no significant effects on the following haematological parameters: erythrocyte count; leucocyte counts (WBC); haematocrit; Hb; mean corpuscular volume; mean corpuscular Hb content; mean corpuscular Hb concentration. However, WBC and respiratory burst activity were significantly affected by dietary FOS supplementation. Evaluation of the cultivable autochthonous intestinal microbiota revealed a significant increase in the levels of total viable heterotrophic aerobic bacteria and lactic acid bacteria in fish fed diets supplemented with 2 and 3 % FOS. Furthermore, dietary FOS supplementation significantly increased the survival rate and stress resistance of carp fry compared with the control treatment. These results encourage conducting further research on the administration of FOS and other prebiotics in carp fry studies.

The human oro-gastrointestinal (GI) tract is a complex system, consisting of oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus, which all together with the accessory digestive organs constitute the digestive system. The function of the digestive system is to break down dietary constituents into small molecules and then absorb these for subsequent distribution throughout the body. Besides digestion and carbohydrate metabolism, the indigenous microbiota has an important influence on host physiological, nutritional and immunological processes, and commensal bacteria are able to modulate the expression of host genes that regulate diverse and fundamental physiological functions. The main external factors that can affect the composition of the microbial community in generally healthy adults include major dietary changes and antibiotic therapy. Changes in some selected bacterial groups have been observed due to controlled changes to the normal diet e.g. high-protein diet, high-fat diet, prebiotics, probiotics and polyphenols. More specifically, changes in the type and quantity of non-digestible carbohydrates in the human diet influence both the metabolic products formed in the lower regions of the GI tract and the bacterial populations detected in faeces. The interactions between dietary factors, gut microbiota and host metabolism are increasingly demonstrated to be important for maintaining homeostasis and health. Therefore the aim of this review is to summarise the effect of diet, and especially dietary interventions, on the human gut microbiota. Furthermore, the most important confounding factors (methodologies used and intrinsic human factors) in relation to gut microbiota analyses are elucidated.

Chronic subcutaneous (s.c.) administration of d-galactose (DG) to BL/6J mice has been shown to induce oxidative stress and is considered a model to mimic accelerated ageing. Fructo-oligosaccharide (FO) is a well-defined prebiotic and its fermentation by lactic acid bacteria has been shown to exert antioxidative capacity. The present study was aimed to determine whether FO attenuated DG-induced oxidative stress and hepatopathy in Balb/cJ mice. Mice (12 weeks of age, n 40) were divided into control (s.c. saline), DG (s.c. 1·2 g/kg body weight), DG+FO (5 %, w/w) and DG+vitamin E (0·2 %, w/w) groups and were killed after 52 d of treatment. Results indicated that DG significantly decreased the hepatic superoxide dismutase and glutathione peroxidase activities. These alterations were ameliorated both by FO and vitamin E. DG increased the hepatic TAG content approximately by 7·2 % compared with the vehicle control, which was in agreement with the histological alteration. FO, similar to vitamin E, almost normalised the hepatic TAG content and ameliorated the histological characteristics of fatty liver. Similarly, the increased plasma alanine aminotransferase activity induced by DG was normalised by FO and vitamin E, respectively. Faecal bifidobacteria counts were greater in the DG+FO and DG+vitamin E groups compared with the DG group, respectively. In conclusion, the present study indicated that FO diminished the altered hepatic antioxidative enzyme activities and morphology caused by chronic DG administration in Balb/cJ mice, partially associated with its prebiotic role in the colon.

Strategies to manipulate the gut microbiota in infancy have been considered to prevent the development of allergic diseases later in life. We aimed to elucidate the effects of maternal dietary supplementation with a prebiotic oligosaccharide on gut microbiota and spontaneously developing atopic dermatitis-like skin lesions in the offspring of NC/Nga mice. Female NC/Nga mice were fed diets either with or without fructo-oligosaccharide supplementation during pregnancy and lactation. After weaning, offspring were fed the diets supplemented with or without fructo-oligosaccharide for 11 weeks in an air-uncontrolled conventional room. Changes in gut microbiota were assessed by denaturing gradient gel electrophoresis of the PCR-amplified 16S rRNA gene. Skin lesions were evaluated by a clinical score and scratching behaviour. Serum antibody levels were measured by ELISA, and expression levels of cytokines and chemokines in lesional tissue were evaluated by quantitative RT-PCR. Maternal supplementation with fructo-oligosaccharide modulated the gut microbiota in sucklings. Although maternal supplementation with fructo-oligosaccharide suppressed the increase in clinical skin severity score and scratching behaviour in offspring, dietary fructo-oligosaccharide after weaning was less effective. The diminution of skin lesions was accompanied by lower serum concentrations of total IgG1 and lower expression levels of TNF-α in the lesional tissue. These data suggest that maternal consumption of fructo-oligosaccharide diminishes the severity of atopic dermatitis-like skin lesions in the offspring of NC/Nga mice.

The gastrointestinal tract is a complex milieu as a result of interaction between dietary ingredients and the intestinal bacteria. Following the European ban on the use of in-feed antibiotics, research has focused mainly on the potentially beneficial activities of the intestinal microbiota. Fermentable carbohydrates, or ‘prebiotics’, such as non-digestible oligosaccharides, are considered to have beneficial effects on the composition and activity of the indigenous microbiota, which can enhance the resistance of the host against colonisation of pathogenic bacteria in the GIT. Only a limited number of prebiotics has been tested in broilers that include fructo-oligosaccharides, inulin, mannan-oligosaccharides, alpha gluco-oligosaccharides, isomalto-oligosaccharides, different kestoses and lactose along with its derivatives. This review provides an overview pertaining to the potential impact of prebiotics on the intestinal bacterial population in broilers and summarizes the data regarding the role of prebiotics in preventing the colonisation of enteropathogens especially Salmonella spp., Campylobacter spp. and Clostridium spp. Moreover, the influence of prebiotics on the intestinal bacterial fermentation profile, particularly short chain fatty acids, ammonia and lactate, is also discussed. Prebiotics have been found to affect the intestinal bacterial population particularly elevating the caecal count of Lactobacillus spp. and Bifidobacterium spp. The effect of prebiotics on the intestinal bacteria is also evident in terms of change in the total concentration or relative proportion of short chain fatty acids. The ability of prebiotics in controlling the colonisation of different enterpathogens especially Salmonella spp., Clostridium perfringens or Campylobacter spp. showed inconsistent results depending upon the available literature.

The isoflavone genistein is found predominantly in soyabeans and is thought to possess various potent biological properties, including anti-carcinogenic effects. Studies have shown that genistein is extensively degraded by the human gut microflora, presumably with a loss of its anti-carcinogenic action. The aim of the present study was to investigate the potential of a prebiotic to divert bacterial metabolism away from genistein breakdown: this may be of benefit to the host. Faecal samples were obtained from healthy volunteers and fermented in the presence of a source of soyabean isoflavones (Novasoy™ (10g/l); ADM Neutraceuticals, Erith, Kent, UK). Bacterial genera of the human gut were enumerated using selective agars and genistein was quantified by HPLC. The experiment was repeated with the addition of glucose (10g/l) or fructo-oligosaccharide (10g/l; FOS) to the fermentation medium. The results showed most notably that counts of Bifidobacterium spp. and Lactobacillus spp. were significantly increased (P<0·05 and P<0·01 respectively) under steady-state conditions in the presence of FOS. Counts of Bacteroides spp. and Clostridium spp. were, however, both significantly reduced (P<0·05) during the fermentation. A decline in genistein concentration by about 52 and 56% over the 120h culture period was observed with the addition of glucose or FOS to the basal medium (P<0·01), compared with about 91% loss of genistein in the vessels containing Novasoy™ (ADM Neutraceuticals) only. Similar trends were obtained using a three-stage chemostat (gut model), in which once again the degradation of genistein was about 22% in vessel one, about 24% in vessel two and about 26% in vessel three in the presence of FOS, compared with a degradation of genistein of about 67% in vessel one, about 95% in vessel two and about 93% in vessel three in the gut model containing Novasoy™ (ADM Neutraceuticals) only. The present study has shown that the addition of excess substrate appeared to preserve genistein in vitro. In particular, the use of FOS not only augmented this effect, but also conferred an additional benefit in selectively increasing numbers of purportedly beneficial bacteria such as bifidobacteria and lactobacilli.

Butyrate is recognised as efficient in healing colonic inflammation, but cannot be used as a long-term treatment. Dietary fibre that produces a high-butyrate level when fermented represents a promising alternative. We hypothesised that different types of dietary fibre do not have the same efficiency of healing and that this could be correlated to their fermentation characteristics. We compared short-chain fructo-oligosaccharides (FOS) and type 3 resistant starch (RS) in a previously described dextran sulfate sodium (DSS)-induced colitis model. Seventy-two Sprague–Dawley rats received water (control rats) or DSS (50g DSS/l for 7d then 30g DSS/l for 7 (day 7) or 14 (day 14) d). The rats were fed a basal diet (BD), or a FOS or RS diet creating six groups: BD-control, BD-DSS, FOS-control, FOS-DSS, RS-control and RS-DSS. Caeco-colonic inflammatory injuries were assessed macroscopically and histologically. Short-chain fatty acids (SCFA) were quantified in caeco-colon, portal vein and abdominal aorta. At days 7 and 14, caecal and distal macroscopic and histological observations were improved in RS-DSS compared with BD-DSS and also with FOS-DSS rats. Caeco-colonic SCFA were reduced in FOS-DSS and RS-DSS groups compared with healthy controls. The amount of butyrate was higher in the caecum of the RS-DSS rats than in the BD-DSS and FOS-DSS rats, whereas distal butyrate was higher in FOS-DSS rats. Partially explained by higher luminal levels of SCFA, especially butyrate, the healing effect of RS confirms the involvement of some types of dietary fibre in inflammatory bowel disease. Moreover, the ineffectiveness of FOS underlines the importance of the type of dietary substrate.