Caloric value of inulin and oligofructose.
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Dietary carbohydrates, which are absorbed as hexose, (glucose, fructose) have a caloric value of 3.9 kcal/g (16.3 kJ/g), and their cellular metabolism produces approximately 38 mol ATP/mol. However, chicory inulin and oligofructose resist digestion and they are not absorbed in the upper part of the gastrointestinal tract. After oral ingestion, they reach the colon intact where they become hydrolyzed and extensively fermented by saccharolytic bacteria, which produce short-chain carboxylic and lactic acids as electron sinks. Depending on both the degree of their colonic fermentation and the assumptions of the model used, the caloric value of such nondigested but fermented carbohydrates varies between 0 and 2.5 kcal/g. Through the catabolism of the absorbed short-chain carboxylic and lactic acids, they may produce up to 17 mol ATP/mol of fermented sugar moiety. Because the daily intake of these dietary carbohydrates is likely to remain relatively small (<10% and probably often not >5% of total daily calorie intake), it is of low relevance nutritionally to give them a precise caloric value. On the basis of biochemical balance charts for carbon atoms, metabolic pathways and energy yields to the host, the caloric value of a fructosyl residue in chicory inulin and oligofructose has been calculated to be approximately 25-35% that of a fully digested and absorbed fructose molecule. For the purpose of food labeling, it is recommended that chicory inulin and oligofructose, like all the other carbohydrates that are more or less completely fermented in the human colon, should be given a caloric value of 1.5 kcal/g (6.3 kJ/g). (+info)
Dietary modulation of the human gut microflora using the prebiotics oligofructose and inulin.
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Although largely unproven in humans, better resistance to pathogens, reduction in blood lipids, antitumor properties, hormonal regulation and immune stimulation may all be possible through gut microflora manipulation. One approach advocates the oral intake of live microorganisms (probiotics). Although the probiotic approach has been extensively used and advocated, survivability/viability after ingestion is difficult to guarantee and almost impossible to prove. The prebiotic concept dictates that non viable dietary components fortify certain components of the intestinal flora (e.g., bifidobacteria, lactobacilli). This concept has the advantage that survival of the ingested ingredient through the upper gastrointestinal tract is not a prerequisite because it is indigenous bacterial genera that are targeted. The feeding of oligofructose and inulin to human volunteers alters the gut flora composition in favor of bifidobacteria, a purportedly beneficial genus. Future human studies that exploit the use of modern molecular-based detection methods for bacteria will determine the efficacy of prebiotics. It may be possible to address prophylactically certain gastrointestinal complaints through the selective targeting of gut bacteria. (+info)
Dose-response effects of inulin and oligofructose on intestinal bifidogenesis effects.
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Recent studies have identified several beneficial attributes of inulin (I) and oligofructose (OF) in human health. However, most of the studies pertaining to the physiologic role of these compounds have been conducted at higher concentrations (8-40 g/d) as a source of dietary fiber. There is growing interest in using I and OF as a substrate for the selective growth of beneficial gastrointestinal bacteria such as the bifidobacteria. In vitro fermentation studies using fecal inoculums have shown that I and OF are utilized rapidly and completely by intestinal microflora and that the degree of polymerization of the substrate influenced its rate of disappearance. In these and other studies, I and OF were shown to be efficient substrates for the growth of most strains of bifidobacteria compared with glucose. In vivo studies have also shown that when human volunteers ingested I or OF, the number of fecal bifidobacteria increased. However, when results from the reported studies are combined and analyzed, a dose-response relationship in terms of log increases in the count of bifidobacteria cannot be demonstrated. Initial numbers of bifidobacteria in the feces, independent of the dose of the fructo-oligosaccharides, seem to influence the results. Future investigations should consider this relationship carefully. (+info)
The application of ecological principles and fermentable fibers to manage the gastrointestinal tract ecosystem.
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Because diet can influence the structure and functions of the gastrointestinal tract, there are opportunities for using diet as a "management tool" to affect the resident microbiota. Fermentable fibers increase the densities of beneficial bacteria and stimulate growth and functions of the healthy intestine. Recent findings show that after acute diarrhea, the use of an oral electrolyte solution with the fermentable fiber oligofructose accelerates recovery of beneficial bacteria, reduces the relative abundance of detrimental bacteria, stimulates mucosal growth and enhances digestive and immune functions. This review will focus on how the principles of stream ecology can be applied to better understand the distribution of bacteria along the length of the gastrointestinal tract, the effect of diarrhea on the gastrointestinal ecosystem and how fermentable fibers can be used as a "management tool" to promote gastrointestinal health in normal states and during recovery from diarrhea. (+info)
Impact of nondigestible carbohydrates on serum lipoproteins and risk for cardiovascular disease.
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Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in the U.S. and in most developed countries. Many nutritional factors contribute to risk for ASCVD including total and saturated fat consumption, fruits and vegetables in the diet and dietary fiber intake. This review will focus on the relationship of dietary fiber intake to risk for coronary heart disease (CHD) and ASCVD (which includes, principally, CHD, cerebral vascular disease and peripheral vascular disease). Fiber-rich foods such as vegetables, fruits, whole-grain cereals and legumes are rich sources of nutrients, phytochemicals and antioxidants. For example, most high fiber foods contain soluble and insoluble fiber, minerals, vitamins, other micronutrients and phytochemicals. Cereals and legumes also contain complex carbohydrates and unsaturated fatty acids. Some high fiber foods are rich in monounsaturated fatty acids, whereas others provide (n-3) fatty acids. Legumes and certain vegetables provide oligosaccharides. When assessing the health benefits of dietary fiber, one should consider the potential effects of associated nutrients, micronutrients and phytochemicals. These interactions will be reviewed as we discuss relationships of dietary fiber to ASCVD. (+info)
Control of lactate production by Selenomonas ruminantium: homotropic activation of lactate dehydrogenase by pyruvate.
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Selenomonas ruminantium produced one mole of D(-)-lactate per mole of glucose used at all dilution rates in ammonia-limited continuous culture. In contrast, lactate production varied according to the dilution rate when glucose was the limiting nutrient. At dilution rates of less than 0.2 h-1, acetate and propionate were the main fermentation products and lactate production was low. At dilution rates above 0.2 h-1, the pattern changed to one of high lactate production similar to that under ammonia limitation. Experiments with cell-free extracts of S. ruminantium showed that D(-)-lactate dehydrogenase had sigmoidal kinetics consistent with homotropic activation of the enzyme by its substrate, pyruvate. This feature allows S. ruminantium to amplify the effects of relatively small changes in the intracellular concentration of pyruvate to cause much larger changes in the rate of production of lactate. Some confirmation that this mechanism of control occurs under physiological conditions was obtained in glucose-limited culture, in which the sigmoidal increase in lactate production was accompanied by a linear increase in pyruvate excretion as the dilution rate increased. (+info)
A cellulolytic anaerobic bacterium, strain I77R1BT, was isolated from a biomat sample of an Icelandic, slightly alkaline, hot spring (78 degrees C). Strain I77R1BT was rod-shaped, non-spore-forming, non-motile and stained Gram-negative at all stages of growth. It grew at 45-82 degrees C, with an optimum growth temperature around 78 degrees C. At 70 degrees C, growth occurred at pH 5.8-8.0, with an optimum near pH 7.0. At the optimum temperature and pH, with 2 g cellobiose l-1 as substrate, strain I77R1BT had a generation time of 2 h. During growth on Avicel, strain I77R1BT produced acetate, hydrogen and carbon dioxide as major fermentation products together with small amounts of lactic acid and ethanol. The strain fermented many substrates, including cellulose, xylan, starch and pectin, but did not grow with casein peptone, pyruvate, D-ribose or yeast extract and did not reduce thiosulfate to H2S. The G+C ratio of the cellular DNA was 35 mol%. Comparative 16S rDNA analysis placed strain I77R1BT among species of Caldicellulosiruptor. The closest relative was Caldicellulosiruptor lactoaceticus. Hybridization of total DNA showed 42% hybridization to C. lactoaceticus and 22% hybridization to Caldicellulosiruptor saccharolyticus. A new species, Caldicellulosiruptor kristjanssonii sp. nov. (I77R1BT) is proposed. (+info)
Sulfidogenesis from 2-aminoethanesulfonate (taurine) fermentation by a morphologically unusual sulfate-reducing bacterium, Desulforhopalus singaporensis sp. nov.
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A pure culture of an obligately anaerobic marine bacterium was obtained from an anaerobic enrichment culture in which taurine (2-aminoethanesulfonate) was the sole source of carbon, energy, and nitrogen. Taurine fermentation resulted in acetate, ammonia, and sulfide as end products. Other sulfonates, including 2-hydroxyethanesulfonate (isethionate) and cysteate (alanine-3-sulfonate), were not fermented. When malate was the sole source of carbon and energy, the bacterium reduced sulfate, sulfite, thiosulfate, or nitrate (reduced to ammonia) but did not use fumarate or dimethyl sulfoxide as a terminal electron acceptor for growth. Taurine-grown cells had significantly lower adenylylphosphosulfate reductase activities than sulfate-grown cells had, which was consistent with the notion that sulfate was not released as a result of oxidative C-S bond cleavage and then assimilated. The name Desulforhopalus singaporensis is proposed for this sulfate-reducing bacterium, which is morphologically unusual compared to the previously described sulfate-reducing bacteria by virtue of the spinae present on the rod-shaped, gram-negative, nonmotile cells; endospore formation was not discerned, nor was desulfoviridin detected. Granules of poly-beta-hydroxybutyrate were abundant in taurine-grown cells. This organism shares with the other member of the genus Desulforhopalus which has been described a unique 13-base deletion in the 16S ribosomal DNA. It differs in several ways from a recently described endospore-forming anaerobe (K. Denger, H. Laue, and A. M. Cook, Arch. Microbiol. 168:297-301, 1997) that reportedly produces thiosulfate but not sulfide from taurine fermentation. D. singaporensis thus appears to be the first example of an organism which exhibits sulfidogenesis during taurine fermentation. Implications for sulfonate sulfur in the sulfur cycle are discussed. (+info)