Slower Fermentation Rate Research Articles

Periodic on-off operations of the self-cycling ethanol fermentation process: Stability analysis and optimal operation strategies

Fuel ethanol is highlighted for being renewable and carbon neutral, but a multi-scale challenge exists that hampers its role as a future energy substitute, and with the breakthrough of cellulose pretreatment and enzyme hydrolysis technology, fermentation itself has become one of the main limiting factors for process enhancement. To tackle the problem, this paper studies periodic operation strategies to improve process performance and avoid possible instabilities. Firstly, superiority by periodic operation over the corresponding steady-state operation is verified. Then, to settle the problem of possible instabilities under impulsive control, stability of state-impulsive control is conducted and for the studied case, any self-cycling fermentation starts from batch mode with 50 % discharge-and-refill portion exhibits superior repeatability property, which allows continuous fermentation to operate under very slow overall dilution rate to cope with the extreme slow fermentation rate. Finally, on-off operation problem is formulated that is governed by a multidimensional nonlinear system, affine to the manipulated variable that is under the isoperimetric constraint; with the use of Pontryagin maximum principle, the optimal synthesis of the optimal strategies under integral constraint is computed out, and a practically plausible on-off operation strategy for ethanol fermentation is formulated with guaranteed periodic stability and optimality.

Structure properties of Canna edulis RS3 (double enzyme hydrolysis) and RS4 (OS-starch and cross-linked starch): Influence on fermentation products and human gut microbiota

This study investigated the in vitro fermentation characteristics of different structural types of Canna edulis resistant starch (RS). RS3 was prepared through a double enzyme hydrolysis method, and RS4 (OS-starch and cross-linked starch) was prepared using octenyl succinic anhydride and sodium trimetaphosphate/sodium tripolyphosphate, respectively. The RS3 and RS4 samples were structurally analyzed using scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction analysis. This was followed by in vitro fermentation experiments. The results revealed microstructure differences in the two groups of starch samples. Compared to native starch, RS3 and RS4 exhibited a lower degree of order and endothermic energy, with lower crystallinity (RS3: 29.59 ± 1.11 %; RS4 [OS-starch]: 28.01 ± 1.32 %; RS4 [cross-linked starch]: 30.44 ± 1.73 %) than that in native starch (36.29 ± 0.89 %). The RS content was higher in RS3 (63.40 ± 2.85 %) and RS4 (OS-starch: 71.21 ± 1.28 %; cross-linked starch: 74.33 ± 0.643 %) than in native starch (57.71 ± 2.95 %). RS3 and RS4 exhibited slow fermentation rates, promoting the production of short-chain fatty acids. RS3 and cross-linked starch significantly increased the production of acetate and butyrate. Moreover, RS3 significantly promoted the abundance of Lactobacillus, while OS-starch and cross-linked starch significantly enhanced the abundance of Dorea and Coprococcus, respectively. Hence, the morphological structure and RS content of the samples greatly influenced the fermentation rate. Moreover, the different varieties of RS induced specific gut microbial regulation. Hence, they show potential applications in functional foods for tailored gut microbiota management.

In vitro digestion under simulated saliva, gastric and small intestinal conditions and fermentation of nicotinamide mononucleotide, and its effects on the gut microbiota

Nicotinamide Mononucleotide (NMN) is a derivative of vitamin B3, which plays a significant role in a plethora of metabolic reactions in the human body and is intricately associated with both immunity and metabolism. Nonetheless, in the intestine metabolic pathway of NMN and the relationship between NMN, gut microbiota, and SCFAs remain hitherto obscure. This study examined the digestion of NMN in simulated saliva, gastric, and small intestine environments, as well as exploring the interaction between NMN and human gut microbiota utilizing an in vitro fermentation model. NMN was progressively degraded into nicotinamide ribose (NR), nicotinamide (NAM), and ribose, with niacinate (NA) constituting the ultimate degradation product due to hydrolysis and metabolism by microbiota. NMN was ingested by human intestinal microbiota with a slower fermentation rate. As a result of NMN ingestion by human gut bacteria，the concentrations of propionate and butyrate increased by 88% and 23%, respectively, compared to the blank control group, the proliferation of beneficial gut bacteria (Bifidobacterium, Phascolarctobacterium, Faecalibacteriun, and Alistipes) significantly increased, while the proliferation of some harmful bacteria (Sutterella, Desulfovibrio and Pseudomonas) drastically declined. These findings illustrated the metabolic processes of NMN in the intestine, elaborating the relationship between NMN, SCFAs and gut microbiota. NMN might be a potential prebiotic to improve intestinal health.

Characterization and in vitro digestion of rice starch/konjac glucomannan complex prepared by screw extrusion and its impact on gut microbiota

In this paper, we prepared a series of rice starch complexed with various konjac glucomannan (KGM) contents under screw extrusion. The complex's multiscale structures, rheological and thermal properties, and in vitro digestion were explored. The complex's effects on short-chain fatty acids production and gut microbiota composition were further investigated using in vitro human fecal fermentation. Multi-scale structural analysis indicated that short-ordered degree, single/double helix structure contents, and crystallinity of the rice starch increased with an increased concentration of KGM. Rheology and differential scanning calorimeter analysis indicated that KGM enhanced the viscoelasticity of rice starch paste and the thermal stability of rice starch. In vitro digestion data revealed that as KGM concentrations increased, both slowly digested component (SDC) and resistant component (RC) contents increased. This phenomenon was ascribed to the complexation of KGM with rice starch assisted by screw extrusion. Further, the high RC content of the complex contributed to the yield of butyrate level, corresponding to the growth in Actinobacteria at the phylum level, and Megasphaera and Bifidobacterium at the genus level in the cultures. Overall, this research will be critical in determining the physicochemical properties and fecal fermentation behaviors of the rice starch–KGM complex and creating starchy foods with specific health benefits. • Rice starch/Konjac glucomannan (KGM) complex was prepared by screw extrusion. • KGM improved the functional properties of the rice starch during screw extrusion. • Rice starch-KGM complexes presented a slow fermentation rate and similar SCFAs yields. • The complex altered the metabolome, and the changes correlated with those in gut microbiota.

In vitro digestion and fecal fermentation of highly resistant starch rice and its effect on the gut microbiota

Highly resistant starch rice (HRSR) is of particular interest in terms of its capacity to deliver short-chain fatty acids (SCFAs) to the colon in the prevention of diabetes mellitus and obesity. In this study, HRSR was processed into cooked rice, rice milk, rice cake, and rice popcorn, and the in vitro digestion and fermentation processes were monitored. The results showed that the starch digestibility of the four samples conformed to a first-order two-phase equation, and the resistant starch content of rice cake was the highest (11.98%). Compared with inulin, rice cake had a slower fermentation rate, and the butyrate concentration increased by 67.85%. The abundances of Prevotellaceae, which promotes the synthesis of SCFAs, and anti-inflammatory Faecalibacterium increased. The abundances of Proteobacteria and Megamonas, markers of gut microbiota imbalance, decreased. The results might facilitate the design and production of functional food products for type 2 diabetic and obese patients and improving colonic health.

Engineering enhanced anaerobic digestion: Benefits of ethanol fermentation pretreatment for boosting direct interspecies electron transfer

Conversion of organic wastes to methane via anaerobic digestion has been practiced for more than 160 years. However, the technical bottlenecks derived from the thermodynamic limitations of interspecies hydrogen/formate transfer (IHT/IFT) between syntrophs and methanogens resulting in the slow fermentation rate, low methane conversion efficiency and poor stability of system still limit its large-scale application. No engineering strategy to speed up IHT/IFT for dramatically changing the performances of anaerobic digestion has been developed. However, recent studies documented that simply pretreating organic wastes to produce ethanol could effectively accelerate and stabilize anaerobic digestion. This may be linked to the promotion of direct interspecies electron transfer (DIET), an alternative working mode that no longer requires hydrogen or formate as an electron carrier. Further information on how this strategy affects the function of methanogenic communities to clarify its advantages is required. In this study, we summarized the evidence that pretreating organic wastes to produce ethanol enhanced anaerobic digestion, discussed the link between ethanol and DIET, and emphasized how this strategy would be better applied in the future.

Fermentation Kinetics of Selected Dietary Fibers by Human Small Intestinal Microbiota Depend on the Type of Fiber and Subject.

ScopeAn underexplored topic is the investigation of health effects of dietary fibers via modulation of human small intestine (SI) microbiota. A few previous studies hint at fermentation of some dietary fibers in the distal SI of humans and pigs. Here the potential of human SI microbiota to degrade dietary fibers and produce metabolites in vitro is investigated.Methods and ResultsFructans, galacto‐oligosaccharides, lemon pectins, and isomalto/malto‐polysaccharides are subjected to in vitro batch fermentations inoculated with ileostomy effluent from five subjects. Fiber degradation products, formation of bacterial metabolites, and microbiota composition are determined over time. Galacto‐ and fructo‐oligosaccharides are rapidly utilized by the SI microbiota of all subjects. At 5h of fermentation, 31%–82% of galacto‐oligosaccharides and 29%–89% fructo‐oligosaccharides (degree of polymerization DP4‐8) are utilized. Breakdown of fructo‐oligosaccharides/inulin DP ≥ 10, lemon pectin, and iso‐malto/maltopolysaccharides only started after 7h incubation. Degradation of different fibers result in production of mainly acetate, and changed microbiota composition over time.ConclusionHuman SI microbiota have hydrolytic potential for prebiotic galacto‐ and fructo‐oligosaccharides. In contrast, the higher molecular weight fibers inulin, lemon pectin, and iso‐malto/maltopolysaccharides show slow fermentation rate. Fiber degradation kinetics and microbiota responses are subject dependent, therefore personalized nutritional fiber based strategies are required.

Direct interspecies electron transfer in anaerobic digestion: Research and technological application

Anaerobic digestion (AD), an economical and eco-friendly strategy for renewable energy recovery, has been widely investigated and applied in the stabilization of various organic wastes. However, two major factors involved in the slow fermentation rate and low methane conversion efficiency still limit its large-scale applications around the world. Methane formation via conventional methanogenic pathway in AD undergoes the three stages: Hydrolysis/acidogenesis, acetogenesis and methanogenesis. The structure of some saccharide- and protein-like organic compounds contained in complex organic waste is relatively complex and stable, limiting the rate of converting them into amino acids, fatty acids and alcohols by fermentative bacteria. Therefore, the hydrolysis/acidogenesis is widely recognized as a rate-limiting step of AD in practical applications. On the other hand, the obligate anaerobic methanogens can only utilize methanol, methylamine, formate, acetate and hydrogen/carbon dioxide as substrates. Methane formation with amino acids, fatty acids and alcohols as substrates requires the essential conversion of them into acetate and hydrogen/carbon dioxide by acetogenic bacteria, and then depends on acetate- and hydrogen-utilizing methanogens to metabolize acetate and hydrogen/carbon dioxide into methane, respectively. This working mode of syntrophic metabolism of organic compounds into methane between acetogenic bacteria and methanogens that depends on hydrogen as an interspecies electron carrier has been widely described as Interspecies Hydrogen Transfer (IHT). Formate may be also served as a substitute for hydrogen as an interspecies electron carrier (Interspecies Formate Transfer, IFT). Syntrophic metabolism of organic compounds is strictly limited by the hydrogen partial pressure, since the oxidation of organic compounds into acetate with H+ as an electron acceptor is not feasible in thermodynamics ( E H + / H 2 = −0.414 V, pH 7). Syntrophic metabolism via IHT functions well as long as the hydrogen-utilizing methanogens continuously maintain the hydrogen partial pressure low enough (

Chemical Cross-Linking Controls in Vitro Fecal Fermentation Rate of High-Amylose Maize Starches and Regulates Gut Microbiota Composition.

A slow fermentation rate of dietary fiber could result in a steady metabolite production release and even distribution in the entire colon, increasing the likelihood of meeting the energy requirements of the distal colon. In the present study, we modulated the fermentation rate in an in vitro human fecal fermentation model by applying chemical cross-linking modification to a type 2 resistant starch [i.e., high-amylose maize starch (HAMS)]. Cross-linking modification decreased the gas production (an indicator of the fermentation rate) of HAMS throughout the whole fermentation progress. The butyrate production rate of cross-linked starches decreased gradually with the increase of the cross-linking degree. Certain beneficial gut microbiota such as genera of Blautia and Clostridiales members were remarkably promoted by starches with low and medium cross-linking degrees, whereas HAMS with a high cross-linking degree obviously promoted the abundance of Bacteroides uniformis and Ruminococcus bromii. This finding reveals that cross-linking modification effectively controls the fermentation rate and highlights the modulation metabolite profiles and gut microbiota composition through chemical modification.

Alterations in the amounts of microbial metabolites in different regions of the mouse large intestine using variably fermentable fibres

Understanding the fermentation profiles of dietary fibres in the different regions of the large intestine is needed to design dietary strategies for desired outcomes related to health such as targeting region-specific diseases. In order to test how variably fermentable dietary fibres affect microbial fermentation metabolites in different regions of the large intestine, mice were fed with fructooligosaccharides (FOS, fast fermentation rate), resistant starch type 2 (native potato, RS2, moderate fermentation rate), starch-entrapped microspheres (SM, very slow fermentation rate), and lignin (control) for 14 days. Analysis of intestinal contents obtained from the cecum, proximal colon, and distal colon revealed that short-chain fatty acid (SCFA) metabolites as well as branched-chain fatty acids (BCFA) levels in different regions of the large intestine were influenced by fibre type and rate of fermentation. Slower fermenting resistant starch-based fibres (RS2 and SM) produced more butyrate than FOS in the proximal and distal colon regions. SM substantially lowered the amount of total BCFAs in the distal colon compared to FOS, suggesting that SM promotes delayed saccharolytic activity throughout the colon. Moreover, the microbial analysis done with length-heterogeneity-PCR showed that all fermentable substrates shifted the microbial community with respect to the control group. Overall, our findings show that the type and amount of SCFAs and BCFAs generated in different regions of the large intestine is dietary fibre type and fermentation rate dependent, which should be considered for increasing the health promoting effects of dietary fibres.

Adding granular activated carbon into anaerobic sludge digestion to promote methane production and sludge decomposition

Anaerobic digestion of waste activated sludge is frequently restricted with the slow fermentation rate due to its complex components. Carbon materials have been reported to enhance syntrophic metabolism of anaerobic wastewater treatment, but its function in anaerobic digestion of sludge has yet to be investigated. In this study granular activated carbon (GAC) was added into a batch-mode anaerobic sludge digestion reactor with an attempt to improve the sludge digestion. The results showed that with adding GAC from 0 to 5.0 g, the methane production increased by 17.4%, and the sludge reduction rate increased by 6.1 percent points (from 39.1% to 45.2%). In the 20 days’ digestion, GAC obviously enriched hydrogen-utilizing methanogens, Geobacter, and other methanogens capable of direct interspecies electron transfer, which could enhance the electron exchange between syntrophs and methanogens to accelerate substrate consumption and methane production.

Understanding medusahead low intake and palatability through in vitro digestibility and fermentation kinetics

The low intake of medusahead grass (Taeniatherum caput-medusae ssp. asperum) by sheep is attributed to the high silica content of the plant and its negative impact on digestibility, making this weed a successful competitor in grazed plant communities. The goals of this study were to determine the influence of (1) plant maturity stage (from late vegetative stage to beginning of senescence and thatch), (2) particle size (1, 5, 10 and 20 mm), and (3) high-quality feeds (alfalfa hay and a high-energy concentrate) on fermentation kinetics and apparent digestibility of medusahead relative to palatable feeds (alfalfa and tall fescue hays, and high-energy concentrates). In vitro gas production was estimated and apparent digestible organic matter (DOM) of the substrates was assessed after incubation. Medusahead from late vegetative to senescence stage had greater DOM (65% to 71%; P<0.05) than alfalfa hay (53%), similar to tall fescue hay (67%; P>0.05), and lower than the high-energy concentrates assayed (77% to 79%; P<0.05). Fermentation kinetics showed slow fermentation rates for medusahead relative to alfalfa (P<0.05), and a decline in fermentation rates with plant maturity (P<0.05). Fermentation rates of the substrates were reduced with particle sizes ⩾5 mm (P<0.05), and apparent DOM for medusahead declined as particle size increased, a relationship not found for alfalfa or tall fescue hays (P<0.05). No effects (P>0.05) on digestibility parameters were observed by the addition of high-quality feeds to medusahead. Slow fermentation kinetics and a significant inhibitory effect of particle size on apparent digestibility of organic matter contribute to explain the low use of medusahead by sheep. Such inhibitory effect may also underlie the lack of positive associative effects observed during the study.

Comparative transcriptomes reveal novel evolutionary strategies adopted by Saccharomyces cerevisiae with improved xylose utilization capability

Production of ethanol from xylose by recombinant Saccharomyces cerevisiae is suboptimal with slow fermentation rate, compared with that from glucose. In this study, a strain-expressing Scheffersomyces stipitis xylose reductase-xylitol dehydrogenase (XR-XDH) pathway was subjected to adaptive evolution on xylose; this approach generated populations with the significantly improved cell growth and ethanol production rate. Mutants were isolated, and the best one was used for sporulation to generate eight stable mutant strains with improved xylose fermentation ability. They were used in a microarray assay to study the molecular basis of the enhanced phenotype. The enriched transcriptional differences among the eight mutant strains and the native strain revealed novel responses to xylose, which likely contributes to the improved xylose utilization. The upregulated vitamin B1 and B6 biosynthesis indicated that thiamine served as an important cofactor in xylose metabolism and may alleviate the redox stress. The increased expression of genes involved in sulfur amino acid biosynthesis and the decreased expression of genes related to Fe(II) transport may alleviate redox stress as well. Meanwhile, it was remarkable that several glucose-repressible genes, including genes of the galactose metabolism, gluconeogenesis, and ethanol catabolism, had a lower expression level after adaptive evolution. Concomitantly, the expression levels of two regulators of the glucose signaling pathway, Rgs2 and Sip4, decreased, indicating a reshaped signaling pathway to xylose after adaptive evolution. Our findings provide new targets for construction of a superior bioethanol producing strain through inverse metabolic engineering.

Adsorption of butanol vapor on active carbons with nitric acid hydrothermal modification

Butanol can be produced from biomass via fermentation and used in vehicles. Unfortunately, butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Butanol can be efficiently removed from fermentation broth by gas stripping, thereby preventing its inhibitory effects. Original active carbon (AC) and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb butanol vapor. The specific surface area and oxygen-containing functional groups of AC were tested before and after modification. The adsorption capacity of unmodified AC samples was the highest. Hydrothermal oxidation of AC with HNO3 increased the surface oxygen content, Brunauer–Emmett–Teller (BET) surface area, micropore, mesopore and total pore volume of AC. Although the pore structure and specific surface area were greatly improved after hydrothermal oxidization with 4M HNO3, the increased oxygen on the surface of AC decreased the dynamic adsorption capacity.

Structural features of soluble cereal arabinoxylan fibers associated with a slow rate of in vitro fermentation by human fecal microbiota

Most soluble dietary fibers ferment rapidly in the proximal colon, potentially causing discomfort and poor tolerability. Alkali-extracted arabinoxylan isolates from corn, wheat, rice and sorghum brans were prepared, through hydrolysis (except sorghum) and ethanol fractionation, to have a broad range of initial fermentation rates, and their linkage patterns were determined to understand structural aspects related to slow fermentation rate. They were all highly branched polymers with degree of substitution greater than 64%. There was no relationship of molecular mass, arabinose:xylose ratio, or degree of substitution to fermentation rate patterns. Slow fermenting wheat and corn arabinoxylans had much higher amount of terminal xylose in branches than fast fermenting rice and sorghum arabinoxylans. The slowest fermenting wheat arabinoxylan additionally contained a complex trisaccharide side chain with two arabinoses linked at the O-2 and O-3 positions of an arabinose that is O-2 linked to the xylan backbone. Structural features were proposed for tolerable slowly fermentable arabinoxylan with possible beneficial fermentation function into the distal colon.

THE EFFECT OF DELIGNIFICATION PROCESS WITH ALKALINE PEROXIDE ON LACTIC ACID PRODUCTION FROM FURFURAL RESIDUES

Furfural residues produced from the furfural industry were investigated as a substrate for lactic acid production by simultaneous saccharification and fermentation (SSF). Alkaline peroxide was used for delignification of furfural residues to improve the final lactic acid concentration. The residue was treated with 1.3% to 1.7% hydrogen peroxide at 80 °C for 1 h with a substrate concentration of 3.33%. SSF of furfural residues with different delignification degrees were carried out to evaluate the effect of delignification degree on lactic acid production. Using corn hydrolysates/ furfural residues as substrates, SSF with different media were carried out to investigate the effect of lignin on the interaction between enzymes and lactic acid bacteria. Lactic acid bacteria had a negative effect on cellulase, thus resulting in the reduction of enzyme activity. Lignin and nutrients slowed down the decreasing trend of enzyme activity. A higher delignification resulted in a slower fermentation rate and lower yield due to degradation products of lignin and the effect of lignin on the interaction between enzymes and lactic acid bacteria. For the purpose of lactic acid production, a moderate delignification (furfural residues with the lignin content of 14.8%) was optimum.

Germ‐Derived FAN as Nitrogen Source for Corn Endosperm Fermentation

ABSTRACTCorn endosperm separated by dry fractionation could exhibit poor fermentation performance due to loss of germ components beneficial for yeast growth. Inorganic nitrogen and other nutritional supplementations are used to overcome slow fermentation rates. We investigated the use of a protease in generating free amino nitrogen (FAN) from germ as an alternative to exogenous nitrogen sources. Up to 300% more FAN can be generated from germ in 6 hr of incubation with protease than without protease. Protease incubation also resulted in higher dry solids (ds) and total glucose contents in the germ hydrolyzates. During fermentation without urea addition, ethanol yields were dependent on mash FAN concentrations. Ethanol yields increased to a maximum when FAN level was 80–90 mg of FAN/100 g ds. At half the optimal FAN level (≈40 mg of FAN/100 g ds), nitrogen limitation occurred, as indicated by high residual glucose concentrations. However, germ FAN did not increase the ethanol yields compared to urea supplementation, likely because germ FAN resulted in lower substrate consumption compared to urea supplementation. Lower substrate consumption correlated to the increase in residual maltose with increase in initial FAN. Ethanol productivity in 0–24 hr of fermentation was higher with germ FAN than with urea, thus decreasing overall fermentation time.

How does pattern of feeding and rate of nutrient delivery influence conditioned food preferences?

Ruminant herbivores have been shown to learn about food properties by associating food flavours with the food's post-ingestive consequences. Previous experimentation supporting the conditioned food aversion/preference hypothesis has generally employed very simple diet learning tasks which do not effectively represent the wide range of foods selected within single bouts typical of wild, free-ranging ruminant herbivores. We tested the ability of a ruminant herbivore to associate a food with artificially administered nutrient rewards in a designed experiment where we altered the temporal pattern of encounter with the food as well as the nature (fast or slow reward) of the post-ingestive outcome. Twenty-four goats were offered branches of Sitka spruce (SS) and Norway spruce (NS) for 4 h per day on two days per week for five weeks. The pattern of feeding varied with treatment such that the species on offer changed every hour (short) or every 2 h (long). The energy treatment altered the reward delivered during Sitka consumption so that animals were dosed either with predominantly sugar (rapidly fermented), predominantly starch (slower fermentation rate), or with water (placebo). Preference was measured on the day following each learning day. We expected that goats would find it easier to associate SS with post-ingestive rewards when the duration of encounter was longest, and that associations would be stronger with the most rapidly digested post-ingestive reward. In the event, goats did not alter their consumption of SS in response to the treatments. Our results suggest that at the scale of temporal resolution of encounters with different plant species (1-2 h), and at the different rates of experiencing post-ingestive consequences tested in this experiment, ruminants do not appear to discriminate the nutritive properties of foods predominantly through a post-ingestive feedback mechanism. They must, instead, use a range of cues-including post-ingestive consequences-to assess food properties.

In vitro fecal fermentation of alginate‐starch microspheres shows slow fermentation rate and increased production of butyrate

The development of dietary fibers with slow fermentation profiles that deliver desirable fermentation products, such as butyrate, to distal regions of the colon may be beneficial for colonic health. The purpose of this study was to determine whether alginate-entrapped starch might be used for such a designed dietary fiber. Alginate-starch microspheres were prepared from 1, 2, or 3% alginate and 10% starch. A blank was also prepared using only alginate. Samples were subjected to in vitro digestion and fermentation. A sample of normal corn starch was included as a control. During fermentation, total gas volume was measured using a graduated syringe, and short chain fatty acids (SCFAs) were quantified by gas chromatography. Alginate entrapment significantly reduced starch digestion to less than 20%. During fermentation, higher alginate concentrations significantly reduced both the total and rate of gas production. This implies that the starch microspheres would not contribute to the uncomfortable bloating experienced with many dietary fibers. Increasing alginate concentration changed the rate of SCFA production from a parabolic to more linear profile, while simultaneously and substantially increasing the proportion of butyrate (of total SCFAs) produced. This suggests than starch entrapment may allow for a significant and constant, slow delivery of butyrate throughout the colon.

Inulin-type fructans of longer degree of polymerization exert more pronounced in vitro prebiotic effects

We assessed to what extent fructans of different degrees of polymerization (DP) differ in their prebiotic effectiveness towards in vitro microbial communities from the proximal and distal colon. Two short chain fructans - oligofructose (DP 2-20) and inulin (DP 3-60) - were administered to the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) at 2.5 g day(-1). The influence of fructan addition towards fermentation activity and microbial community composition from the different SHIME colon compartments were evaluated. Both fructans exerted prebiotic effects with significantly higher butyrate and propionate production and stimulation of lactic acid-producing bacteria. Compared with oligofructose, it was noted that it took more time before significant effects from inulin addition were observed. Yet, the higher short-chain fatty acid production and lower proteolytic activity showed that the prebiotic effects from inulin were more pronounced than oligofructose. Also, the bifidogenic effects from inulin vs oligofructose were higher in the distal colon compartments and this effect was prolonged in the distal colon once the addition was stopped. Inulin has more pronounced prebiotic effects than oligofructose towards both fermentation activity and bacterial community composition in the SHIME model. Its slower fermentation rate and higher prebiotic potency makes inulin a more interesting compound than oligofructose to beneficially influence the microbial community from both the proximal and distal colon regions.