In vitro prebiotic effects of Acacia gums onto the human intestinal microbiota depends on both botanical origin and environmental pH

Acacia gums are commonly used food additives. It is currently unclear how extensively these non-digestible polysaccharides are fermented in the human large intestine. However, they have been shown to support bifidobacterial growth in vitro and may represent useful candidate prebiotics. In these investigations, in vitro 24-h batch incubations and chemostat continuous-cultures of human faecal bacteria were conducted using two acacia gums (Fibregum standard and Fibregum AS). Our aim was to study the effects of these gums on bacterial ecology and fermentation in the large bowel. Fructooligosaccharides (Actilight-950P) were also investigated as a reference. Both Acacia gums were extensively fermented by intestinal flora although there were marked differences in fermentation product formation and ecological effects, probably due to their differing botanical origins and/or biochemical characteristics. In particular, fermentation of Fibregum AS led to significantly higher proportions of propionate both in batch and chemostat experiments. Both gums decreased Clostridium sp. levels but only Fibregum-standard induced higher Lactobacillus sp. counts compared to control. These bacterial modifications were highly dependent of the operating pH of the fermentation system with acidic conditions promoting both the prebiotic and the butyrogenic effects of fructooligosaccharides. In these studies, we have demonstrated that, similarly to fructooligosaccharides, Acacia gums can exert putatively beneficial effects on host health through both the improvement of the composition of the large intestine microflora and SCFA formation.     

Computation of pH evolution versus ionic products concentration in a fermentation broth

An algorithm developed for pH computation has been tested to calculate the theoretical pH changes in a culture medium during the course of a fermentation. A divergence between the computed pH value and the value measured with the electrode allows us to highlight the presence of undetected ionic products. The calculation with the algorithm by means of a computer requires only the knowledge of the ionic properties of the substrates and detected products and existing thermodynamic constants. (c) 1993 Wiley & Sons, Inc.     

Effect of initial pH independent of operational pH on hydrogen fermentation of food waste

The effect of initial pH from 5.0 to 9.0 on H₂ fermentation of food waste was investigated. In this batch experiment, however, unlike previous studies for initial pH, operational pH was maintained at 5.0 by the addition of alkaline solution. Although the period for pH drop from the initial values to 5.0 was less than one-tenth of the entire fermentation, this short period significantly affected the H₂ production performance. At initial pH 6.0-9.0, successful H₂ yield of 1.3-1.9 mol H₂/mol hexose_added was achieved with a peak value at pH 8.0. The H₂ yield achieved at initial pH 8.0 was corresponded to the 8.13% of total energy content in the substrate. At initial pH 5.0, the smallest butyrate production, but the highest ethanol production was detected, indicating unfavorable conditions for H₂ production. There was no significant relationship between total required amount of alkaline solution and initial pH values.     

Propionic acid fermentation of lactose by Propionibacterium acidipropionici: effects of pH

Batch propionic acid fermentation of lactose by Propionibacterium acidipropionici were studied at various pH values ranging from 4.5 to 7.12. The optimum pH range for cell growth was between 6.0 and 7.1, where the specific growth rate was approximately 0.23 h(-1). The specific growth rate decreased with the pH in the acids have been identified as the two major fermentation products from lactose. The production of propionic acid was both growth and nongrowth associated, while acetic acid formation was closely associated with cell growth. The propionic acid yield increased with decreasing pH; It changed from approximately 33% (w/w) at pH 6.1-7.1 to approximately 63% at pH 4.5-5.0. In contrast, the acetic acid yield was not significantly affected by the pH; it remained within the range of 9%-12% at all pH values. Significant amounts of succinic and pyruvic acids were also formed during propionic acid fermentation of lactose. However, pyruvic acid was reconsumed and disappeared toward the end of the fermentation. The succinic acid yield generally decreased with the pH, from a high value of 17% at pH 7.0 to a low 8% at pH 5.0 Effects of growth nutrients present in yeast ex-tract on the fermentation were also studied. In general, the same trend of pH effects was found for fermentations with media containing 5 to 10 g/L yeast extract. However, More growth nutrients would be required for fermentations to be carried out efficienytly at acidic pH levels.     

Influence of pH regulation and nutrient content on cephalosporin C production in solid-state fermentation by Acremonium chrysogenum C10

Aims: To investigate the effect of pH regulation and nutrient concentration on cephalosporin C (CPC) production in solid‐state fermentation (SSF), using sugarcane bagasse as inert support, impregnated with liquid medium. Methods and Results: Solid‐state fermentation using different initial pH values, buffer and nutrient concentrations were performed. Results revealed pH as a key parameter in CPC SSF, as it hampered the antibiotic production not only above 7·8, but also under 6·4. Using initial pH lower than 6·8 and PB in the solid medium, it was possible to keep pH within the production range, increase the production period (from 1 to 3 days) and hence the CPC yield from 468 to 3200 μg gdm^?1 (g^?1 of dry matter). Conclusion: Parameters that help to keep pH in adequate values for CPC production in SSF, such as initial pH, buffering system and nutrient concentration, can greatly increase the production time and CPC yields in this fermentation technique. Significance and Impact of the Study: This is the first work on CPC production on impregnated support, and the only one revealing pH as a key parameter; it is also shown that high nutrient concentration can improve CPC yields in SSF as long as pH is kept under control.     

In vitro appraisal of the probiotic value of intestinal lactobacilli

Lactobacilli play a distinctive role in the microbial balance of the chicken gut. In experiments simulating the chicken crop, the antagonism of lactobacilli against Enterobacteriaceae and Salmonella typhimurium was demonstrated and was attributed to lactic acid production. Moreover, adhesion to the crop epithelium was a common characteristic of intestinal lactobacilli. As opposed to salmonellas, lactobacilli were sensitive to deconjugated bile salts at 2.5mm. This sensitivity could lower their chance of proliferation in the small bowel of the chicken tract.The authors are at the Laboratory of Microbial Ecology, Faculty of Agricultural Sciences, State University of Gent, Coupure L., 653, B-9000 Gent, Belgium.     

pH对克雷伯氏菌1,3-丙二醇合成关键酶酶活及发酵特性的影响

在5 L发酵罐进行甘油脉冲流加发酵,分析了不同pH值对克雷伯氏肺炎杆菌发酵特性的影响,pH 6.5为菌体最佳生长条件,克雷伯氏肺炎杆菌合成1,3-丙二醇的产量最高。在1,3-丙二醇合成速率较大的对数中前期,进行甘油脉冲流加发酵,提高甘油浓度促进甘油脱水酶、1,3-丙二醇氧化还原酶和甘油脱氢酶活性。不同pH值的脉冲试验表明,甘油脱水酶,2,3-丁二醇脱氢酶比酶活随着pH值的升高而升高,1,3-丙二醇氧化还原酶,乳酸脱氢酶比酶活在pH6.5最高,因此偏酸性的发酵条件和对数期维持一定的甘油浓度能够促进1,3-丙二醇的合成。     

In vitro effects of selected synbiotics on the human faecal microbiota composition

Synbiotics are recognized means of modulating gut microbiota composition and activities. However, whether synbiotics are superior to prebiotics and probiotics alone in moderating the gut microbiota towards a purportedly healthy composition has not been determined. Eight selected synbiotics (short-chain fructooligosaccharides or fructooligosaccharides, each combined with one of four probiotics, Lactobacillus fermentum ME-3, Lactobacillus plantarum WCFS1, Lactobacillus paracasei 8700:2 or Bifidobacterium longum 46) were added to 24-h pH-controlled anaerobic faecal batch cultures. The prebiotic and probiotic components were also tested alone to determine their respective role within the synbiotic for modulation of the faecal microbiota. Effects upon major groups of the microbiota were evaluated using FISH. Rifampicin variant probiotic strains were used to assess probiotic levels. Synbiotic and prebiotics increased bifidobacteria and the Eubacterium rectale-Clostridium coccoides group. Lower levels of Escherichia coli were retrieved with these combinations after 5 and 10 h of fermentation. Probiotics alone had little effect upon the groups, however. Multivariate analysis revealed that the effect of synbiotics differed from the prebiotics as higher levels of Lactobacillus-Enterococcus were observed when the probiotic was stimulated by the prebiotic component. Here, the synbiotic approach was more effective than prebiotic or probiotic alone to modulate the gut microbiota.     

Impact of diet and individual variation on intestinal microbiota composition and fermentation products in obese men

There is growing interest in understanding how diet affects the intestinal microbiota, including its possible associations with systemic diseases such as metabolic syndrome. Here we report a comprehensive and deep microbiota analysis of 14 obese males consuming fully controlled diets supplemented with resistant starch (RS) or non-starch polysaccharides (NSPs) and a weight-loss (WL) diet. We analyzed the composition, diversity and dynamics of the fecal microbiota on each dietary regime by phylogenetic microarray and quantitative PCR (qPCR) analysis. In addition, we analyzed fecal short chain fatty acids (SCFAs) as a proxy of colonic fermentation, and indices of insulin sensitivity from blood samples. The diet explained around 10% of the total variance in microbiota composition, which was substantially less than the inter-individual variance. Yet, each of the study diets induced clear and distinct changes in the microbiota. Multiple Ruminococcaceae phylotypes increased on the RS diet, whereas mostly Lachnospiraceae phylotypes increased on the NSP diet. Bifidobacteria decreased significantly on the WL diet. The RS diet decreased the diversity of the microbiota significantly. The total 16S ribosomal RNA gene signal estimated by qPCR correlated positively with the three major SCFAs, while the amount of propionate specifically correlated with the Bacteroidetes. The dietary responsiveness of the individual''s microbiota varied substantially and associated inversely with its diversity, suggesting that individuals can be stratified into responders and non-responders based on the features of their intestinal microbiota.     

3-羟基丙酸分批发酵过程中的pH控制策略研究

本文利用重组大肠杆菌以甘油为底物发酵合成3．羟基丙酸,考察了不同pH对3．羟基丙酸产量及菌体生长的影响,发现在pH6．5条件下,细胞比生长速率达到最大值,延迟期也相对较短;而pH7．0有利于3-羟基丙酸的合成,控制pH7．0可以使3-羟基丙酸产量达到7．39g／L。基于不同pH条件下对细胞比生长速率和3-羟基丙酸比生成速率的分析,提出3．羟基丙酸分批发酵过程中的pH控制策略,即在发酵过程前5h将pH控制在6．5,5h～15h控制pH为7．0,此时有利于细胞生长;而后在15h-25h控制pH为7．5,25h后控制pH为7．0,从而使细胞具有较高的3．羟基丙酸比合成速率。在此控制策略下经过34h发酵3-羟基丙酸的终产量达到8．76g／L,比pH7．0条件下的3-羟基丙酸产量提高了18．54％。     

On the use of the pH control reagent addition rate for fermentation monitoring

The linear relation between the pH control reagent addition rate, the net conversion rates of metabolites, the carbon dioxide mass transfer rate and the feed rates is developed and shown to have the same form for batch, fed-batch, and continuous reactors, regardless of the number of feeds. The magnitudes of various biological and solution chemistry effects on the pH control reagent addition rate are estimated to be negligible, facilitating the use of the pH control reagent addition rate as a straightforward indicator of primary metabolism. Finally, application of the linear relation, termed the abiotic proton balance, is discussed for a number of fermentation processes. (c) 1995 John Wiley & Sons, Inc.     

Maturation of the murine cecal microbiota as revealed by terminal restriction fragment length polymorphism and 16S rRNA gene clone libraries

The maturation of murine cecal microbiota was determined by terminal restriction fragment polymorphism (T-RFLP) and 16S rRNA gene clone libraries. Cecal microbiota in specific pathogen free (SPF) mice aged four to 10 weeks were collected. The cluster of samples in 4-week-old mice was different from those of other ages based on T-RFLP profiles. The majority of clones obtained in this study belonged to the Clostridium coccoides (C. coccoides) group, the Bacteroides group or the Lactobacillus group. Phylogenetic analysis showed characteristic clusters composed of new operational taxonomic unit (OTU) of the C. coccoides and Bacteroides groups. The existence of a large number of yet unidentified bacteria inhabiting the murine cecum was demonstrated by 16S rRNA gene clone libraries. T-RFLP analysis data were more complex and more sensitive than the patterns generated by computer simulation of 16S rRNA gene clone library analysis data. T-RFLP revealed development with maturation of cecal microbiota including unidentified bacteria of SPF mice.     

The influence of narrow-leafed lupin seed fermentation on their chemical composition and ileal digestibility and microbiota in growing pigs

The aims of this study were to provide a controlled fermentation process of blue lupin seeds (Lupinus angustifolius, cv. Neptun), monitor the changes in seed composition and determine the influence of the fermentation on the apparent ileal digestibility (AID) of crude protein (CP) and amino acids in growing pigs, compared with raw lupin seeds. The fermentation with bacteria and yeast was conducted for 24 h at 25ºC under aerobic conditions. Seed fermentation increased the contents of CP, fibre, fat and ash and most of the analysed amino acids but reduced the levels of the nitrogen-free extractives. Furthermore, fermentation decreased the contents of raffinose family oligosaccharides and phytic acids but increased the alkaloid content. The AID was estimated on three barrows (mean initial body weight 25 kg), surgically fitted with a T-cannula in the distal ileum. The pigs received three diets, each for 6 d, within three experimental periods (3 × 3 Latin Square design). The diets contained soybean meal (Group SBM), raw lupin seeds (Group RL) or fermented lupin seeds (Group FL) as solely protein sources. Fermentation had a positive impact on the AID of CP and methionine, cysteine, isoleucine, leucine, phenylalanine and valine (p < 0.05). Feeding raw or fermented lupin seeds did not affect the microbial status of the ileal digesta. Moreover, ammonia content in the caecal digesta did not differ between Groups RL and FL, although it was significantly higher than in Group SBM. It can be concluded that the fermentation process modified the chemical composition of nutrients in seeds, which can influence the digestibility and utilisation of the fermentation product in animal diets compared to raw seeds.     

Effects of Enterococcus faecium and dried whey on broiler performance,gut histomorphology and intestinal microbiota

Abstract

The experiment was conducted to study the effects of supplementing a broiler starter diet with the probiotic Enterococcus faecium NCIMB 10415 and dried whey (80% lactose) on chick performance, gut histomorphology and intestinal microbiota. One-day-old male Ross 308 strain broiler chickens were fed diets containing: (i) control feed, (ii) control + 3.5% dried whey, (iii) control + 0.2%E. faecium, and (iv) control + 3.5% dried whey + 0.2%E. faecium. Birds were maintained in battery brooders confined in an environmentally controlled experimental room. The experiment lasted for 21 days. Birds fed E. faecium or E. faecium + dried whey exhibited significantly improved weight gain and feed conversion rate (FCR). Weight gain and FCR of treatment groups 1 – 4 were 628.7, 657.8, 690.9, 689.3 and 1.218, 1.193, 1.107, 1.116, respectively. Lactic acid bacteria counts in both the ileal content and excreta were significantly affected by dietary treatment. Supplementation of the E. faecium and dried whey separately and in combination increased lactic acid bacteria colonization in the ileal content from 4.2 to 5.0, 7.8 and to 5.1 log cfu/g, respectively (treatments 1 – 4). Similarly, supplementation of dried whey and E. faecium separately and in combination increased lactic acid bacteria in the excreta from 5.3 to 5.5, 8.0 and to 7.2 log cfu/g, respectively. Addition of the probiotic E. faecium increased villus height in the ileum (p < 0.05). Thus, supplementation of E. faecium enhanced broiler chick performance with respect to weight gain and FCR. No additive effect of E. faecium and dried whey was detected. Further studies are needed to investigate the relationship between E. faecium and dried whey with respect to gut histomorphology.     

In vitro fermentation of linear and alpha-1,2-branched dextrans by the human fecal microbiota

The role of structure and molecular weight in fermentation selectivity in linear α-1,6 dextrans and dextrans with α-1,2 branching was investigated. Fermentation by gut bacteria was determined in anaerobic, pH-controlled fecal batch cultures after 36 h. Inulin (1%, wt/vol), which is a known prebiotic, was used as a control. Samples were obtained at 0, 10, 24, and 36 h of fermentation for bacterial enumeration by fluorescent in situ hybridization and short-chain fatty acid analyses. The gas production of the substrate fermentation was investigated in non-pH-controlled, fecal batch culture tubes after 36 h. Linear and branched 1-kDa dextrans produced significant increases in Bifidobacterium populations. The degree of α-1,2 branching did not influence the Bifidobacterium populations; however, α-1,2 branching increased the dietary fiber content, implying a decrease in digestibility. Other measured bacteria were unaffected by the test substrates except for the Bacteroides-Prevotella group, the growth levels of which were increased on inulin and 6- and 70-kDa dextrans, and the Faecalibacterium prausnitzii group, the growth levels of which were decreased on inulin and 1-kDa dextrans. A considerable increase in short-chain fatty acid concentration was measured following the fermentation of all dextrans and inulin. Gas production rates were similar among all dextrans tested but were significantly slower than that for inulin. The linear 1-kDa dextran produced lower total gas and shorter time to attain maximal gas production compared to those of the 70-kDa dextran (branched) and inulin. These findings indicate that dextrans induce a selective effect on the gut flora, short-chain fatty acids, and gas production depending on their length.     

Studies on the effects of selenium on rumen microbial fermentation in vitro

The effects of selenium (Se) on ruminant microbial fermentation were investigated in vitro using rumen microflora collected from a rumen-fistulated dairy cow. First, the effects ofl-selenomethionine (SeMet; at 0.2 or 2 ppm Se) in the presence or absence of wheat bran (WB, 500 mg per incubation flask) were evaluated. Second, the effects of several forms of Se (elemental Se: 50 ppm Se; sodium selenite: 2 ppm Se; SeMet: 2 ppm Se) were compared. Results showed that the amounts of short-chain fatty acids (SCFAs) tended to be increased by SeMet treatment, whereas SeMet in the presence of WB transiently suppressed fermentation. The addition of SeMet tended to increase the production of acetate while reducing the production of butyrate with and without WB supplementation. Among the different Se compounds tested, the amounts of SCFAs were greater with SeMet treatment, which yielded a higher proportion of acetate compared to other treatments. Selenite did not influence the total SCFAs concentrations; however, it increased the relative proportion of butyrate at the expense of acetate. Elemental Se did not significantly affect fermentation. Higher bacterial Se concentrations were observed for selenite than for SeMet. It was concluded that Se supplementation can influence rumen microbial fermentation and that Se compounds differ in this regard.     

The role of metal on imide hydrolysis: metal content and pH profiles of metal ion-replaced mammalian imidase

Imidase catalyzes the hydrolysis of a variety of imides. The removal of metal from imidase eliminates its activity but does not affect its tetrameric and secondary structure. The reactivation of the apoenzyme with transition metal ions Co(2+), Zn(2+), Mn(2+), and Cd(2+) shows that imidase activity is linearly dependent on the amount of metal ions added. Ni(2+) and Cu(2+) are also inserted, one per enzyme subunit, into the apoimidase, but do not restore imidase activity. Enzyme activity with different metal replaced imidase varies significantly. However, the changes of the metal contents do not appear to affect the pK(a)s obtained from the bell-shaped pH profiles of metal reconstituted imidase. The metal-hydroxide mechanism for imidase action is not supported based on the novel findings from this study. It is proposed that metal ion in mammalian imidase functions as a Lewis acid, which stabilizes the developing negative charge of imide substrate in transition state.     

Parameters of fermentation and rumen microbiota of Nellore steers fed with different proportions of concentrate in fresh sugarcane containing diets

The objective of this study was to evaluate the effect of a fresh sugarcane-based diet and different roughage-to-concentrate ratios (70:30, 60:40, 40:60 and 20:80) on the rumen microbiota associated with rumen fermentation parameters and the intake and apparent digestibility of nutrients in Nellore steers. Eight rumen-cannulated Nellore steers (331 ± 8 kg BW) were distributed in a double 4 × 4 Latin square design balanced for the control of the residual effect. The ruminal pH decreased (p < 0.01) and the concentrations of N–NH₃, isovaleric and valeric acids increased linearly (p < 0.05) with an increase dietary concentrate level. Furthermore, an increased concentrate proportion reduced the population of Fibrobacter succinogenes and Ruminococus flavefaciens (p < 0.01) and increased the population of Selenomonas ruminantium and Megasphaera elsdenii (p < 0.01). The protozoa count revealed a predominance of the genus Entodinium. The synthesis of microbial N [g/d] and the efficiency of microbial synthesis [g of microbial N/kg of organic matter apparently digested in the rumen] increased as the proportion of concentrate was increased (p < 0.05). Therefore, it can be concluded that an increasing proportion of concentrate in sugarcane-containing diets enhances the synthesis of microbial protein and does not alter the fibre digestibility, although the population of fibre fermenting bacteria was reduced.