Five European laboratories tested a simple in vitro batch system for dietary fibre fermentation studies, The inoculum was composed of fresh human faeces mixed with a carbonatephosphate buffer complex supplemented with trace elements and urea. Five dietary fibre sources (cellulose, sugarbeet fibre, soyabean fibre, maize bran and pectin) were used by each laboratory on three occasions to determine pH, residual non-starch polysaccharides (NSP) and short-chain fatty acid production during fermentation. Cellulose and maize bran degradabilities were very low (7.2 (SE 10.8) and 6 2 (SE 9.1) % respectively after 24h), whereas pectin and soyabean fibre were highly degraded (97.4 (~~4 . 4 ) and 91.1 ( s~3 . 4 ) % respectively after 24 h). Sugarbeet fibre exhibited an intermediate level of degradability (595 (SE 149) %). Short-chain fatty acid production was closely related to NSP degradation (r 0.99). Although each variable was ranked similarly by all laboratories, some differences occurred with respect to absolute values. However, the adaptation of donors to the experimental substrates was not an influential factor. Interlaboratory differences could be reduced either by adding less substrate during incubations or using less-diluted inocula. In vitro fermentations with inocula made from human faeces and from rat caecal contents gave similar results. There was a close correspondence between the data obtained in the present experiment and those previously published in in vivo studies in the rat using the same fibres. The in v i m batch system tested during the present study provides a rapid means of obtaining quantitative estimates of the fermentation and the estimation of the energy content of new sources of dietary fibre.
Chemical and physical transformations of solid food begin in the mouth, but the oral phase of digestion has rarely been studied. In the present study, twelve healthy volunteers masticated mouthfuls of either bread or spaghetti for a physiologically-determined time, and the levels of particle degradation and starch digestion before swallowing were compared for each food. The amounts of saliva moistening bread and spaghetti before swallowing were, respectively, 220 (SEM 12) v. 39 (SEM 6) g/kg fresh matter. Particle size reduction also differed since bread particles were highly degraded, showing a loss of structure, whereas spaghetti retained its physical structure, with rough and incomplete reduction of particle size. Starch hydrolysis was twice as high for bread as for spaghetti, mainly because of the release of high-molecular-mass a-glucans. The production of oligosaccharides was similar after mastication of the two foods, respectively 125 (SEM 8) and 92 (SEM 7) g/kg total starch. Starch hydrolysis, which clearly began in the mouth, depended on the initial structure of the food, as in the breakdown of solid food. These significant physical and chemical degradations of solid foods during oral digestion may influence the entire digestive process.
Considering the effects of some fermentation products on intestinal morphology and finction, these variations may be relevant to the pathogenesis of colorectal diseases.
The aim of the present study was to assess the relationship between the disappearance of dietary fibre sugars and the production of individual short-chain fatty acids (SCFA). The bacterial degradation of five dietary fibres whose sugars were quantified was investigated in vitro using a human faecal inoculum. Involvement of the main fibre sugars in SCFA production was evaluated by a stepwise multiple linear regression. The results show first that the nature and chiefly the associations between the fibre sugars were key variables in the fermentability. Second, the nature and the amounts of SCFA produced were closely related to the in vitro fermentation of the main sugars available: uronic acids seemed to be principally involved in the production of acetic acid whereas the production of propionic acid could be promoted by the fermentation of glucose and, to a lesser extent, by that of xylose and arabinose. Xylose tended to have a greater impact than uronic acids and glucose on the production of butyric acid. Thus, it would be possible to predict which SCFA could be specifically produced during the fermentation of a fibre, as far as the chemical composition and structure of this fibre are known.
Objective: This study investigated whether postprandial metabolic responses to bread could be lowered by substituting high amylose maize starch for a part of the¯our. Design and subjects: Eight healthy subjects consumed test meals of equivalent nutritional composition based on white wheat bread, bread rich in amylose (HAWB) and spaghetti as a breakfast meal. Blood samples were collected to measure insulin and glucose concentration during two hours after consumption. The degree of starch crystallinity was investigated by X-ray diffraction and DSC analysis. Results: HAWB produced low glycaemic (60 AE 18) and insulinaemic (57 AE 20) indexes similar to those of spaghetti (83 AE 46, 61 AE 16). In vitro amylase hydrolysis of the three foods showed that high amylose content in HAWB signi®cantly lowered starch degradation in bread without affecting hydrolysis kinetics. Addition of amylose in dough increased the resistant starch content of HAWB (14% of dry matter). The resistant starch fraction was mainly composed of crystalline amylose (B-type X-ray diffraction pattern, melting temperature 105 C) attributable to native high amylose maize starch incompletely gelatinised during bread-cooking. Conclusions: Bread produced by the substitution of high amylose maize starch for a part of wheat¯our showed a low glycaemic index. Resistant starch in HAWB corresponded to native crystalline amylose not gelatinised during normal bread-processing conditions.
In order to assess the relationship between methane (CH4) producing status and the breath excretion of hydrogen (H2) in healthy subjects, breath CH4 and H2 were simultaneously measured for 14 hours after oral ingestion of 10 g lactulose in 65 young volunteers. Forty were breath CH4 producers and 25 were not. Statistically significant differences were observed between both groups, with lower values for CH4 producers recorded for the foliowing parameters: fasting basal value of breath H2 (8.1 (4.9) v 5-2 (3.7) ppm, p<005), mouth-to-caecum transit time (68 (24) The hydrogen (H2) and methane (CH4) produced in the human body derive entirely from colonic anaerobic bacterial fermentation. While most of these gases are consumed on site or excreted in flatus, the part expelled by the lungs can be easily collected and measured by endexpiratory sampling.'2 H2 production increases when a fermentable carbohydrate is incompletely absorbed in the small intestine, forming the basis for the use of the H2 breath test. This non-invasive procedure has been extensively used in clinical practice3'" and pharmacological studies'2 to measure mouth-to-caecum transit time. It has also been proposed as a semi quantitative method for evaluating intestinal malabsorption of carbohydrates.'314 The recent development of a simple gas analyser not only offers the opportunity to measure breath H2 but breath CH4 as well. Although the substrates for CH4 production are not yet fully identified,2 '5 it has been shown that in Caucasian adults, only 30%-50% are breath CH4 producers, whereas 90%-98% excrete breath H2.'622 In most previously published investigations, however, little attention has been paid to the relationship between breath CH4 producing status and the H2 excretion profile after lactulose administration. In a previous study evaluating starch malabsorption of pasta,23 we observed different patterns of H2 production according to breath CH4 producing status, a finding which has also been described in preliminary studies by other authors. 16 20 24 This prompted us to prospectively assess the relationship between breath CH4 producing status and the breath excretion of H2 in healthy subjects. Methods SUBJECTSSixty five subjects (32 men, 33 women) ranging from 19 to 30 years (mean 22 4 (2)) were selected from a population of healthy volunteers without known disease and free from gastrointestinal symptoms as previously tested in our laboratory. In addition, their breath CH4 producing status was already known. Forty were breath CH4 producers as defined below. Their breath samples were compared with those of 25 healthy controls who were breath CH4 non-producers. All volunteers were French born Caucasians of similar ethnic origin. As enemas, laxatives, and antibiotics can affect the colonic microflora and, hence, the production of intestinal gas,25 any individual receiving these treatments within three months before the study was excluded. All subjects gave their informed consent to the study protocol which had been approved by the Ethics ...
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