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.

Partially hydrolysed guar gum (PHGG), a water-soluble dietary fibre produced by the controlled partial enzymatic hydrolysis of guar gum beans, has various physiological roles. This study aimed to elucidate the beneficial effects of PHGG on colonic mucosal damage in a murine 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis model. Acute colitis was induced in male C57BL/6 mice with TNBS after 2 weeks of pre-feeding with PHGG (5 %). The colonic mucosal inflammation was evaluated using macroscopic damage scores, and neutrophil infiltration was assessed by measuring tissue-associated myeloperoxidase (MPO) activity in the colonic mucosa. TNF-α expression in the colonic mucosa was measured by ELISA and real-time PCR. Moreover, the intestinal microbiota and production of SCFA were assessed by real-time PCR and HPLC, respectively. Colonic damage due to TNBS administration was significantly ameliorated by PHGG treatment. Furthermore, PHGG significantly inhibited increases in MPO activity and TNF-α protein and mRNA expression in the colonic mucosa in TNBS-induced colitis. On analysis of intestinal microbiota, we found that the concentration of the Clostridium coccoides group (Clostridium cluster XIVa), the Clostridium leptum subgroup (Clostridium cluster IV) and the Bacteroides fragilis group had significantly increased in PHGG-fed mice. On analysis of SCFA, we found that the caecal content of acetic acid, propionic acid and butyric acid had significantly increased in PHGG-fed mice. Together, these results suggest that chronic ingestion of PHGG prevents the development of TNBS-induced colitis in mice by modulating the intestinal microbiota and SCFA, which may be significant in the development of therapeutics for inflammatory bowel disease.

Partially hydrolysed guar gum (PHGG), a soluble dietary fibre, has been shown to provide many health benefits. Previous studies had suggested that the combination of PHGG with protein provided a significant satiation effect on visual analogue scales (VAS). What was lacking was only the effect of administration of small doses of PHGG on post-meal satiation and subsequent energy intake. The objectives of the present investigations were to find the subjective perception of post-meal satiety with acute and long term administration of small amounts of PHGG alone with food, its effects on subsequent energy intake and the comparative effects among different types of soluble fibres. The following three separate studies were conducted: in study 1, healthy subjects (n 12) consumed PHGG along with breakfast, lunch and an evening snack; in study 2, healthy subjects (n 24) consumed 2 g of PHGG or dextrin along with yogurt as breakfast for 2 weeks; in study 3, healthy subjects (n 6) took 6 g each of either PHGG or indigestible dextrin or inulin along with lunch. In all the studies, various satiety parameters were measured on VAS before and after consumption of PHGG. The addition of PHGG showed significant (P< 0·05) acute (studies 1 and 3) and long-term (studies 1 and 2) satiety effects compared to the control and/or an equal amount of carbohydrate or other types of soluble fibre. Study 2 also indicated that the prolonged consumption of PHGG may significantly (P< 0·05) reduce energy intake from whole-day snacking. PHGG could be an ideal natural soluble fibre for delivering acute and long term satiety effects for comfortable appetite control.