Propionibacterium acidipropionici CRL1198 influences the production of acids and the growth of bacterial genera stimulated by inulin in a murine model of cecal slurries

Different attempts have been made to improve the health status of humans and animals by increasing the intestinal production of short-chain fatty acids (SCFA) derived from non-digestible carbohydrates fermentation. In this paper we investigate the in vitro production of short-chain fatty acids (SCFA) after addition of inulin, propionibacteria or a combination of both in an experimental model of mice cecal slurries. The development of bacterial genera which are usually stimulated by inulin addition was also investigated. According to our experimental data, acetic acid and butyric acids concentrations increased after incubation in slurries that had no supplements. By contrast, butyric acid concentrations remained in the basal value when supplements were used. Fermentation of only inulin did not increase the concentration of total SCFA. Propionibacterium acidipropionici CRL1198 improved the production of propionic acid in cecal slurries when it was added alone, but the effect was more noticeable in the combination with inulin. A modulation of the global fermentative activity of the cecal microbiota was evidenced by the increase on the ratio propionic acid/SCFA in supplementations with propionibacteria. Statistical analysis of data demonstrated that samples from homogenates with propionibacteria alone or combined with inulin belong to the same cluster. The presence of propionibacteria limited the growth of Bacteroides fragilis and Clostridium hystoliticum groups in slurries with and without inulin. The growth of Bifidobacterium was not modified and the stimulating effect of inulin on lactobacilli disappeared in the presence of propionibacteria. In conclusion, dairy propionibacteria are potential candidates to develop new functional foods helpful to ensure the intestinal production of SCFA during inulin supplementation and to control the overgrowth of bacteria belonging to Bacteroides and Clostridium genera.     

Fibre utilization by Kalahari dwelling subterranean Damara mole-rats (Cryptomys damarensis) when fed their natural diet of gemsbok cucumber tubers (Acanthosicyos naudinianus)

Kalahari dwelling Damara mole-rats (Cryptomys damarensis) naturally feed on a high fibre diet of underground gemsbok cucumber tubers, Acanthosicyos naudinianus. We investigated the degree of fibre utilization and fermentation on this diet by measuring caecal characteristics (namely temperature, pH and weight) and in vitro rates of gas and short chain fatty acid (SCFA) production in these underground dwelling hind-gut fermentors. Rectal temperatures (33.8±0.6°C) were consistently higher than caecal temperatures (33.3 ± 0.6°C). Furthermore, a 0.8°C gradient of temperatures existed within the caecum, with the lowest temperature occurring in the corpus caeci. Both rates of gas production (4.74 ± 0.6 ml/g dry matter/hr) and SCFA production (266.80 ± 9.251 /i mol/caecum per hr) were high, with proportionately more acetic acid produced than any other SCFA. Nevertheless, the initial concentrations of SCFAs present in the caecum were low (52 ±17 mM) implying a rapid rate of absorption of these SCFAs. The high rates of fermentation provide a considerable amount of energy that would otherwise be trapped in fibre and thus unavailable to the animal. This highly efficient caecal fermentation enables the Damara mole-rat to maximally exploit the underground food resources in the arid-zone ecotope.     

Propionic acid production by immobilized cells of a propionate-tolerant strain of Propionibacterium acidipropionici

Cells of the propionate-tolerant strain Propionibacterium acidipropionici P200910, immobilized in calcium alginate beads, were tested for propionic and acetic acid production both in a semidefined laboratory medium and in corn steep liquor in batch, fed-batch, and continuous fermentation. Cell density was about 9.8 × 10⁹ cells/g (wet weight) of beads, and beads were added to the medium at 0.1 g (wet weight) beads/ml. Beads could be reused for several consecutive batch fermentations; propionic acid production in the tenth cycle was about 50%–70% of that in the first cycle. In batch culture complete substrate consumption (glucose in semidefined medium, lactate in corn steep liquor) and maximum acid production were seen within 36 h, and acid yields from the substrate were higher than in free-cell fermentations. Fed-batch fermentations were incubated up to 250 h. Maximum propionic acid concentrations obtained were 45.6 g/l in corn steep liquor and 57 g/l in semidefined medium; this is the highest concentration achieved to date in our laboratory. Maximum acetic acid concentrations were 17 g/l and 12 g/l, respectively. In continuous fermentation of semidefined medium, dilution rates up to 0.31 h^–1 could be used, which gave higher volumetric productivities (0.96 g l^–1 h^–1 for propionic acid and 0.26 g l^–1 h^–1 for acetic acid) than we have obtained with free cells. Corn steep liquor shows promise as an inexpensive medium for production of both acids by immobilized cells of propionibacteria.Journal paper no. J- 15614 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project no. 3122     

Production and recovery of propionic and acetic acids in electrodialysis culture of Propionibacterium shermanii

The simultaneous production and recovery of propionic and acetic acids in cultures of Propionibacterium shermanii were examined while maintaining the concentrations of these acids in the fermentation broth at low values with electrodialysis to alleviate end product inhibition. By this method, maximum cell concentration increased 1.36 fold and the average productivities of propionic and acetic acids increased 1.4 fold and 1.31 fold, respectively, compared to cultures without electrodialysis. The mass ratio of propionic and acetic acids recovered was the same as that for the acids produced by fermentation. The inhibitory effect of propionic acid was more significant on the growth of cells than on the production of propionic acid. Some kinetic equations are presented for simulating the dry cell concentration in the fermentor and the concentrations of propionic and acetic acids in the permeate solution of an electrodialysis culture.     

Propionic acid fermentation by Propionibacterium acidipropionici: effect of growth substrate

Summary Batch propionic acid fermentations by Propionibacterium acidipropionici with lactose, glucose, and lactate as the carbon source were studied. In addition to propionic acid, acetic acid, succinic acid and CO₂ were also formed from lactose or glucose. However, succinic acid was not produced in a significant amount when lactate was the growth substrate. Compared to fermentations with lactose or glucose at the same pH, lactate gave a higher propionic acid yield, lower cell yield, and lower specific growth rate. The specific fermentation or propionic acid production rate from lactate was, however, higher than that from lactose. Since about equimolar acid products would be formed from lactate, the reactor pH remained relatively unchanged throughout the fermentation and would be easier to control when lactate was the growth substrate. Therefore, lactate would be a preferred substrate over lactose and glucose for propionic acid production using continuous, immobilized cell bioreactors. Correspondence to: S. T. Yang     

Fed-batch fermentation with and without on-line extraction for propionic and acetic acid production byPropionibacterium acidipropionici

Fed-batch propionic and acetic acid fermentations were performed in semi-defined laboratory medium and in corn steep liquor withPropionibacterium acidipropionici strain P9. On average, over four experiments, 34.5 g/l propionic acid and 12.8 g/l acetic acid were obtained in about 146 h in laboratory medium with 79 g/l glucose added over five feeding periods. The highest concentration of propionic acid, 45 g/l, was obtained when the glucose concentration was not allowed to drop to zero. In corn steep liquor 35 g/l propionic acid and 11 g/l acetic acid were produced in 108 h from 59.4 g/l total lactic acid provided as seven feedings of corn steep liquor. Extractive fed-batch fermentations were conducted in semi-defined medium using either flat-sheet-supported liquid membranes or hollow-fiber membrane extraction to remove organic acids from the culture medium. As operated during the course of the fermentation, these systems extracted 25% and 22% of the acetic acid and 36.5% and 44.5% of the propionic acid, respectively, produced in the fermentation. Total amounts of acids produced were about the same as in comparable nonextractive fermentations: 30–37 g/l propionic acid and 13 g/l acetic acid were produced in 150 h. Limitations on acid production can be attributed to limited substrate feed, not to failure of the extraction system.Journal paper J-16303 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 3122.     

Effects of soluble fiber inclusion in gestation diets with varying fermentation characteristics on lactational feed intake of sows over two successive parities

The effects of soluble fiber inclusion in gestation diets with varying fermentation characteristics (fermentation kinetics and short-chain fatty acids (SCFA)-profile) on lactational feed intake of sows and their piglet growth over two parities were investigated using an in vitro–in vivo methodology. After breeding, 90 multiparous Landrace sows were randomized to one of three experimental diets: the control (CON) diet, konjac flour (KF) diet or sugar beet pulp (SBP) diet. All diets had similar levels of net energy, CP, insoluble fiber and NDF, but KF and SBP diets had higher soluble fiber levels than the CON diet. During gestation, the sows were restrictively fed with three different diets, but during lactation, all the sows were similarly fed ad libitum. The three gestation diets were enzymatically hydrolyzed using pepsin and pancreatin, and enzymolyzed residues were used in in vitro fermentation. Gas and SCFA production were monitored during fermentation. After fermentation, enzymolyzed residues of KF or SBP diets resulted in higher final asymptotic gas volume than those of the CON diet. The enzymolyzed residues of KF diet were mainly part of rapidly fermented fractions, whereas those of SBP diet were mainly part of slowly fermented fractions. In addition, the acetic acid, butyric acid and total SCFA concentrations of enzymolyzed residues of KF diet were higher (P<0.01) than the control and SBP diets. In the in vivo studies, on day 90 of gestation, the KF diet sows had higher plasma SCFA concentration (P<0.05) at 4 h after feeding than the CON diet sows. Furthermore, the KF diet sows had lower plasma free fatty acid (FFA) concentration (P<0.01) at 4 h after feeding, and a lower value of homeostasis model assessment (HOMA)-insulin resistance (P<0.05), but a higher value of HOMA-insulin sensitivity (P<0.01). The KF diet sows also consumed more feed during lactation (P<0.01) and weaned significantly heavier pigs (P<0.01) than the CON diet sows. The overall results showed that the high fermentation capacity KF diet contributed to an increased lactational feed intake and improved performance of piglets in the second reproductive cycle.     

Propionic Acid Production by a Propionic Acid-Tolerant Strain of Propionibacterium acidipropionici in Batch and Semicontinuous Fermentation

A propionic acid-tolerant derivative of Propionibacterium acidipropionici P9 was obtained by serially transferring strain P9 through broth that contained increasing amounts of propionic acid. After 1 year of repeated transfers, a strain (designed P200910) capable of growth at higher propionic acid concentrations than P9 was obtained. An increase in the proportion of cellular straight-chain fatty acids and uncoupling of propionic acid production from growth were observed for strain P200910. Growth rate, sugar utilization, and acid production were monitored during batch and semicontinuous fermentations of semidefined medium and during batch fermentation of whey permeate for both strain P200910 and strain P9. The highest propionic acid concentration (47 g/liter) was produced by P200910 in a semicontinuous fermentation. Strain P200910 produced a higher ratio of propionic acid to acetic acid, utilized sugar more efficiently, and produced more propionic acid per gram of biomass than did its parent in all fermentations.     

Fermentation properties of gentio-oligosaccharides

AIMS: To investigate the fermentation properties of gentio-oligosaccharides (GOS), as compared to fructo-oligosaccharides (FOS) and maltodextrin in mixed faecal culture. METHODS AND RESULTS: The substrates were incubated in 24 h batch culture fermentations of human faecal bacteria. Fluorescent in situ hybridization was used to determine changes in populations of bifidobacteria, lactobacilli, clostridia, bacteroides, streptococci and Escherichia coli. Gas and short-chain fatty acid (SCFA) production was also measured. GOS gave the largest significant increases in bifidobacteria, lactobacilli and total bacterial numbers during the incubations. However, FOS appeared to be a more selective prebiotic as it did not significantly stimulate growth of bacterial groups which were not probiotic in nature. GOS and maltodextrin produced the highest levels of SCFA. Lowest gas production was seen with GOS and highest with FOS. CONCLUSIONS: GOS possessed bifidogenic activity in vitro. Although fermentation of GOS was not as selective as FOS, gas production was lower. Gas production is often seen as an undesirable side effect of prebiotic consumption. SIGNIFICANCE AND IMPACT OF THE STUDY: The study has provided the first data on fermentation of GOS in mixed faecal culture. The study has also used molecular microbiology methods (FISH) to quantify bacterial groups. The data extend our knowledge of the selectivity of fermentation of oligosaccharides by the gut microflora.     

Fed-batch propionic acid production by Propionibacterium acidipropionici

The batch fermentations were conducted using lactose as the substrate at pH 6.5 and temperature 30°C. Average batch kinetic data was eventually used to develop an unstructured mathematical model. The kinetic parameters of the model were determined by non-linear regression technique using the batch experimental results. Parametric sensitivity analysis showed the maximum specific substrate consumption rate (r_S^max) and the maintenance energy constant (m_S) to be the most sensitive parameters. The experimental observations in batch fermentation were close to the model predictions. The batch model was extrapolated to identify nutrient feeding strategies, which were tested successfully for two different fed-batch fermentations. It demonstrated enhanced propionic acid productivity. The developed model was found suitable for the design of feeding strategies to increase propionic acid production in fed-batch mode of reactor operation.     

The effect of pectin, corn and wheat starch, inulin and pH on in vitro production of methane, short chain fatty acids and on the microbial community composition in rumen fluid

Methane emission from livestock, ruminants in particular, contributes to the build up of greenhouse gases in the atmosphere. Therefore the focus on methane emission from ruminants has increased. The objective of this study was to investigate mechanisms for methanogenesis in a rumen fluid-based in vitro fermentation system as a consequence of carbohydrate source (pectin, wheat and corn starch and inulin) and pH (ranging from 5.5 to 7.0). Effects were evaluated with respect to methane and short chain fatty acid (SCFA) production, and changes in the microbial community in the ruminal fluid as assessed by terminal-restriction fragment length polymorphism (T-RFLP) analysis. Fermentation of pectin resulted in significantly lower methane production rates during the first 10 h of fermentation compared to the other substrates (P = 0.001), although total methane production was unaffected by carbohydrate source (P = 0.531). Total acetic acid production was highest for pectin and lowest for inulin (P < 0.001) and vice versa for butyric acid production from pectin and inulin (P < 0.001). Total propionic acid production was unaffected by the carbohydrate source (P = 0.791). Methane production rates were significantly lower for fermentations at pH 5.5 and 7.0 (P = 0.005), sustained as a trend after 48 h (P = 0.059), indicating that there was a general optimum for methanogenic activity in the pH range from 6.0 to 6.5. Decreasing pH from 7.0 to 5.5 significantly favored total butyric acid production (P < 0.001). Principle component analysis of T-RFLP patterns revealed that both pectin and pH 5.5 resulted in pronounced changes in the microbial community composition. This study demonstrates that both carbohydrate source and pH affect methane and SCFA production patterns, and the microbial community composition in rumen fluid.     

Propionic acid production from glycerol by metabolically engineered Propionibacterium acidipropionici

Large amounts of crude glycerol produced in the biodiesel industry can be used as a low-cost renewable feedstock to produce chemicals and fuels. Compared to sugars (sucrose, glucose, xylose, etc.), glycerol has a lower reducing level, which is of benefit to the production of reduced chemicals. In this work, glycerol as the sole carbon source in propionic acid fermentation by metabolically engineered Propionibacterium acidipropionici (ACK-Tet) was studied. It was found that the adapted ACK-Tet mutant could use glycerol for its growth and produced propionic acid at a high yield of 0.54–0.71 g/g, which was much higher than that from glucose (0.35 g/g). In addition, the production of acetic acid in glycerol fermentation was much less than that from glucose. Thus, glycerol fermentation produced a high purity propionic acid with a high propionic acid to acetic acid ratio of 22.4 (vs. 5 for glucose fermentation), facilitating the recovery and purification of propionic acid from the fermentation broth. The highest propionic acid concentration obtained from glycerol fermentation was 106 g/L, which was 2.5 times of the highest concentration (42 g/L) previously reported in the literature.     

In vitro production of short-chain fatty acids from resistant starch by pig faecal inoculum

The need to improve the knowledge of fermentation processes within the digestive tract in pigs is growing, particularly for ingredients that may act as potential prebiotic sources, such as resistant starch (RS). A study (based on enzymatic digestion followed by in vitro fermentation) was conducted to investigate whether various sources of RS, obtained from eight native starches characterized by inherent heterogeneous starch chemistry and structure, can influence short-chain fatty acid (SCFA) concentrations and relative production kinetics. Total and individual SCFA productions were evaluated over time and up to 72 h of incubation. The in vitro hydrolysis of native starches allowed a classification from very high [⩾650 g/kg dry matter (DM)] to low (<50 g/kg DM) RS amount. The total SCFA production was similar between ingredients, whereas acetate and butyrate molar ratios in the SCFA profile differed (from 0.48 to 0.56 and from 0.17 to 0.25, respectively; P < 0.05). Differences in fermentation kinetic parameters for total and individual SCFA productions were observed (P < 0.05). Considering the total SCFA production after 72 h of incubation, the time at which half of the maximum production has been reached (T_1/2), the maximum rate of production (R_max) and its time of occurrence (T_max) differed between ingredients (P < 0.05), with values ranging from 6.1 to 11.9 h, from 0.459 to 1.300 mmol/g DM incubated per hour and from 5.1 to 9.8 h, respectively. Overall, a similar trend was observed considering individual SCFA productions. In particular, T_1/2 ranged from 6.4 to 12.5 h, from 5.5 to 12.5 h and from 6.7 to 11.3 h for acetate, propionate and butyrate, respectively (P < 0.05). For R_max, differences were obtained for propionate and butyrate productions (P < 0.05), whereas no difference was recorded for acetate. In summary, our findings indicated that both quantitative and qualitative production of SCFA and related kinetics were influenced by fermentation of RS obtained from native starches characterized by heterogeneous starch characteristics. Current findings are based on an in vitro approach, and thus require further in vivo validations.     

Functional Screening and In Vitro Analysis Reveal Thioesterases with Enhanced Substrate Specificity Profiles That Improve Short-Chain Fatty Acid Production in Escherichia coli

Short-chain fatty acid (SCFA) biosynthesis is pertinent to production of biofuels, industrial compounds, and pharmaceuticals from renewable resources. To expand on Escherichia coli SCFA products, we previously implemented a coenzyme A (CoA)-dependent pathway that condenses acetyl-CoA to a diverse group of short-chain fatty acyl-CoAs. To increase product titers and reduce premature pathway termination products, we conducted in vivo and in vitro analyses to understand and improve the specificity of the acyl-CoA thioesterase enzyme, which releases fatty acids from CoA. A total of 62 putative bacterial thioesterases, including 23 from the cow rumen microbiome, were inserted into a pathway that condenses acetyl-CoA to an acyl-CoA molecule derived from exogenously provided propionic or isobutyric acid. Functional screening revealed thioesterases that increase production of saturated (valerate), unsaturated (trans-2-pentenoate), and branched (4-methylvalerate) SCFAs compared to overexpression of E. coli thioesterase tesB or native expression of endogenous thioesterases. To determine if altered thioesterase acyl-CoA substrate specificity caused the increase in product titers, six of the most promising enzymes were analyzed in vitro. Biochemical assays revealed that the most productive thioesterases rely on promiscuous activity but have greater specificity for product-associated acyl-CoAs than for precursor acyl-CoAs. In this study, we introduce novel thioesterases with improved specificity for saturated, branched, and unsaturated short-chain acyl-CoAs, thereby expanding the diversity of potential fatty acid products while increasing titers of current products. The growing uncertainty associated with protein database annotations denotes this study as a model for isolating functional biochemical pathway enzymes in situations where experimental evidence of enzyme function is absent.     

Substrate-limited co-culture for efficient production of propionic acid from flour hydrolysate

Propionic acid is presently mainly produced by chemical synthesis. For many applications, especially in feed and food industries, a fermentative production of propionic acid from cheap and renewable resources is of large interest. In this work, we investigated the use of a co-culture to convert household flour to propionic acid. Batch and fed-batch fermentations of hydrolyzed flour and a process of simultaneous saccharification and fermentation were examined and compared. Fed-batch culture with substrate limitation was found to be the most efficient process, reaching a propionic acid concentration of 30 g/L and a productivity of 0.33 g/L*h. This is the highest productivity so far achieved with free cells on media containing flour hydrolysate or glucose as carbon source. Batch culture and culture with controlled saccharification and fermentation delivered significantly lower propionic acid production (17–20 g/L) due to inhibition by the intermediate product lactate. It is concluded that co-culture fermentation of flour hydrolysate can be considered as an appealing bioprocess for the production of propionic acid.     

Construction of a model of the human proximal colon

The objective of the present study was to construct a system that re-creates the conditions of fermentation and absorption of the human proximal colon. The model was constructed using a glass tube with an internal dialysis membrane tube. The food substrate was fed into the dialysis membrane three times a day simulating a typical human feeding. The substrate contained 58% carbohydrates, 35% proteins, 3% fiber, 3% starch, and 1% lipids on dry weight base, with 90% moisture. The inoculum was a fecal culture propagated in TSB. The intestinal absorption was simulated using a polyethylene glycol (PEG) solution running continuously outside the dialysis membrane. All microorganisms increased their counts after inoculation, and reached higher counts generally after substrate feed. The most important short chain fatty acids (SCFA: acetic, propionic and butyric acids) were analyzed, and their concentrations inside and outside the membrane were significantly different due to the extraction efficiency of the PEG solution. The greatest production occurred at 48 h. SCFA ratios showed that at the beginning, acetate was the predominant compound, but after 12 h the proportion of butyrate increased and the acetate was decreased. This SCFA production pattern is similar to that reported for the proximal colon in live systems. Continuous operation of the colon model for 48 h was enough to reveal the development of microorganisms and SCFA production. This model reproduced the conditions of the human proximal colon adequately and can be used to study the development of colonic microbiota.     

Analysis of fermentation selectivity of purified galacto-oligosaccharides by in vitro human faecal fermentation

The in vitro fermentation of several purified galacto-oligosaccharides (GOS), specifically the trisaccharides 4′-galactosyl-lactose and 6′-galactosyl-lactose and a mixture of the disaccharides 6-galactobiose and allolactose, was carried out. The bifidogenic effect of GOS at 1 % (w/v) was studied in a pH-controlled batch culture fermentation system inoculated with healthy adult human faeces. Results were compared with those obtained with a commercial GOS mixture (Bimuno-GOS). Changes in bacterial populations measured through fluorescence in situ hybridization and short-chain fatty acid (SCFA) production were determined. Bifidobacteria increased after 10-h fermentation for all the GOS substrates, but the changes were only statistically significant (P?<?0.05) for the mixture of disaccharides and Bimuno-GOS. Acetic acid, whose formation is consistent with bifidobacteria metabolism, was the major SCFA synthesized. The acetate concentration at 10 h was similar with all the substrates (45–50 mM) and significantly higher than the observed for formic, propionic and butyric acids. All the purified GOS could be considered bifidogenic under the assayed conditions, displaying a selectivity index in the range 2.1–3.0, which was slightly lower than the determined for the commercial mixture Bimuno-GOS.     

Growth conditions of clostridium perfringens type B for production of toxins used to obtain veterinary vaccines

The diseases caused for Clostridium perfringens are generically called enterotoxemias because toxins produced in the intestine may be absorbed into the general circulation. C. perfringens type B, grown in batch fermentation, produced toxins used to obtain veterinary vaccines. Glucose in concentrations of 1.4–111.1 mM was used to define the culture medium. The minimum concentration for a satisfactory production of vaccines against clostridial diseases was 55.6 mM. Best results were brought forth by meat and casein peptones, both in the concentration 5.0 g l^?1 in combination with glucose and a culture pH maintained at 6.5 throughout the fermentation process. The production of lactic, acetic and propionic organic acids was observed. Ethanol was the metabolite produced in the highest concentration when cultures maintained steady pH of 6.5 with exception of cultures with initial glucose concentration of 1.4 mM, where the highest production was of propionic acid. Maximal cell concentration and the highest toxin title concomitantly low yield coefficient to organic acids and ethanol were obtained using basal medium containing 111.1 mM glucose under a controlled pH culture (pH) 6.5 in batch fermentations of C. perfringens type B. These data contribute to improve process for industrial toxin production allowing better condition to produce a toxoid vaccine.     

Effects of key operational parameters on biohydrogen production via anaerobic fermentation in a sequencing batch reactor

In this study, a series of tests were conducted in a 6 L anaerobic sequencing batch reactor (ASBR) to investigate the effect of pH, hydraulic retention time (HRT) and organic loading rate on biohydrogen production at 28 °C. Sucrose was used as the main substrate to mimic carbohydrate-rich wastewater and inoculum was prepared from anaerobic digested sludge without pretreatment. The reactor was operated initially with nitrogen sparging to form anaerobic condition. Results showed that methanogens were effectively suppressed. The optimum pH value would vary depending on the HRT. Maximum hydrogen production rate and yield of 3.04 L H₂/L reactor d and 2.16 mol H₂/mol hexose respectively were achieved at pH 4.5, HRT 30 h, and OLR 11.0 kg/m³ d. Two relationships involving the propionic acid/acetic acid ratio and ethanol/acetic acid ratio were derived from the analysis of the metabolites of fermentation. Ethanol/acetic acid ratio of 1.25 was found to be a threshold value for higher hydrogen production.     

In vitro fermentation characteristics of selected glucose-based polymers by canine and human fecal bacteria

This research evaluated fermentation characteristics (short-chain fatty acid [SCFA] production, pH, and gas production) resulting from fermentation of glucose-based carbohydrates using canine (n = 3) and human (n = 3) fecal inoculum. Substrates included lyophilized canine ileal digesta containing maltodextrin, gamma-cyclodextrin, high molecular weight (MW) pullulan (MW 100000), or low MW pullulan (MW 6300) obtained from an in vivo experiment. Fermentation for 6 and 10 h with human fecal microflora resulted in higher gas and SCFA production than did canine fecal microflora. High MW pullulan fermentation resulted in the highest (p < 0.05) gas production and lowest (p < 0.05) pH for both dogs and humans. Total SCFA production was highest (p < 0.05) for low MW pullulan fermented by canine microflora, and for gamma-cyclodextrin, high MW pullulan, and low MW pullulan fermented by human microflora. Differences were noted in fermentation characteristics of substrates present in ileal digesta.