Anna Pompei

Fermentation of Fructooligosaccharides and Inulin by Bifidobacteria: a Comparative Study of Pure and Fecal Cultures

ABSTRACT The utilization of fructooligosaccharides (FOS) and inulin by 55 Bifidobacterium strains was investigated. Whereas FOS were fermented by most strains, only eight grew when inulin was used as the carbon source. Residual carbohydrates were analyzed by high-performance anion-exchange chromatography with pulsed amperometric detection after batch fermentation. A strain-dependent capability to degrade fructans of different lengths was observed. During batch fermentation on inulin, the short fructans disappeared first, and then the longer ones were gradually consumed. However, growth occurred through a single uninterrupted exponential phase without exhibiting polyauxic behavior in relation to the chain length. Cellular β-fructofuranosidases were found in all of the 21 Bifidobacterium strains tested. Four strains were tested for extracellular hydrolytic activity against fructans, and only the two strains which ferment inulin showed this activity. Batch cultures inoculated with human fecal slurries confirmed the bifidogenic effect of both FOS and inulin and indicated that other intestinal microbial groups also grow on these carbon sources. We observed that bifidobacteria grew by cross-feeding on mono- and oligosaccharides produced by primary inulin intestinal degraders, as evidenced by the high hydrolytic activity of fecal supernatants. FOS and inulin greatly affected the production of short-chain fatty acids in fecal cultures; butyrate was the major fermentation product on inulin, whereas mostly acetate and lactate were produced on FOS.

Folate Production by Bifidobacteria as a Potential Probiotic Property

ABSTRACT The ability of 76 Bifidobacterium strains to produce folate was investigated. In order to evaluate folic acid productivity, bifidobacteria were cultivated in the folate-free semisynthetic medium SM7. Most of the tested strains needed folate for growth. The production and the extent of vitamin accumulation were not a function of species but were distinctive features of individual strains. Six strains among the 17 that grew without folate produced significantly higher concentrations of vitamin (between 41 and 82 ng ml−1). The effects of exogenous folate and p-aminobenzoic acid (PABA) concentrations on folate production were evaluated. In contrast to most of the other strains, the folate yield of B. adolescentis MB 239 was not negatively affected by either PABA or exogenous folic acid. Folate production by B. adolescentis MB 239 was studied in the pH range of the colonic environment, and a comparison of folate production on raffinose, lactose, and fructo-oligosaccharides, which belong to three important groups of fermentable intestinal carbon sources, was established. Differences in folate biosynthesis by B. adolescentis MB 239 were not observed as a function either of the pH or of the carbon source. Fecal culture experiments demonstrated that the addition of B. adolescentis MB 239 may increase the folate concentration in the colonic environment.

In vitro comparison of the prebiotic effects of two inulin-type fructans

Faecal cultures were used to compare the prebiotic effects of a new fructan containing high solubility inulin (HSI) and of a well-established prebiotic containing oligofructose (OF) with a negative control (CT). Changes in the intestinal microbiota, pH, ammonia, volatile organic acids and lactic acid were monitored during incubation. Molecular techniques for microbial enumeration indicated that both HSI and OF led to a significant increase in bifidobacteria (P< or =0.05) and lactobacilli (P< or =0.05) compared to the control. Significant changes in the pH and levels of ammonia with both inulin-type fructans were observed, as well as higher levels of acetic, lactic and formic acids (P< or =0.05). The fermentative metabolism appeared to be faster on OF than on HSI. Both OF and HSI showed clear prebiotic effects, but had differences in fermentation kinetics because of to the different degree of polymerization (DP). This study provides proof for the prebiotic effectiveness of HSI, and shows that inulin-type fructans with higher DP might have a prolonged bifidogenic effect, thus could extend the saccharolytic metabolism and low pH to the distal parts of the colon.

Substrate preference of Bifidobacterium adolescentis MB 239: compared growth on single and mixed carbohydrates.

The utilization of mono-, di-, and oligosaccharides by Bifidobacterium adolescentis MB 239 was investigated. Raffinose, fructooligosaccharides (FOS), lactose, and the monomeric moieties glucose and fructose were used. To establish a hierarchy of sugars preference, the kinetics of growth and sugar consumption were determined on individual and mixed carbohydrates. On single carbon sources, higher specific growth rates and cell yields were attained on di- and oligosaccharides compared to monosaccharides. Analysis of the carbohydrates in steady-state chemostat cultures, growing at the same dilution rate on FOS, lactose, or raffinose, showed that monomeric units and hydrolysis products were present. In chemostat cultures on individual carbohydrates, B. adolescentis MB 239 simultaneously displayed α-galactosidase, β-galactosidase, and β-fructofuranosidase activities on all the sugars, including monosaccharides. Glycosyl hydrolytic activities were found in cytosol, cell surface, and growth medium. Batch experiments on mixtures of carbohydrates showed that they were co-metabolized by B. adolescentis MB 239, even if different disappearance kinetics were registered. When mono-, di-, and oligosaccharides were simultaneously present in the medium, no precedence for monosaccharides utilization was observed, and di- and oligosaccharides were consumed before their constitutive moieties.

An embedded portable biosensor system for bacterial concentration detection.

Microbial screening is a primary concern for many products. Traditional techniques based on standard plate count (SPC) are accurate, but time consuming. Furthermore, they require a laboratory environment and qualified personnel. The impedance technique (IT) looking for changes in the electrical characteristics of the sample under test (SUT) induced by bacterial metabolism represents an interesting alternative to SPC since it is faster (3-12h vs. 24-72 h for SPC) and can be easily implemented in automatic form. With this approach, the essential parameter is the time for bacteria concentration to reach a critical threshold value (about 10(7) cfu mL(-1)) capable of inducing significant variations in the SUT impedance, measured by applying a 100 mV peak-to-peak 200 Hz sinusoidal test signal at time intervals of 5 min. The results of this work show good correlation between data obtained with the SPC approach and with impedance measurements lasting only 3h, in the case of highly contaminated samples (10(6) cfu mL(-1)). Furthermore, this work introduces a portable system for impedance measurements composed of an incubation chamber containing the SUT, a thermoregulation board to control the target temperature and an impedance measurement board. The mix of cheap electronics and fast detection time provides a useful tool for microbial screening in industrial and commercial environments.

Growth kinetics on oligo- and polysaccharides and promising features of three antioxidative potential probiotic strains.

Aims:  To determine the antioxidative activity, glutathione production, acid and bile tolerance and carbohydrate preferences of Lactobacillus plantarum LP 1, Streptococcus thermophilus Z 57 and Bifidobacterium lactis B 933.

Detection of microbial concentration in ice-cream using the impedance technique.

The detection of microbial concentration, essential for safe and high quality food products, is traditionally made with the plate count technique, that is reliable, but also slow and not easily realized in the automatic form, as required for direct use in industrial machines. To this purpose, the method based on impedance measurements represents an attractive alternative since it can produce results in about 10h, instead of the 24-48h needed by standard plate counts and can be easily realized in automatic form. In this paper such a method has been experimentally studied in the case of ice-cream products. In particular, all main ice-cream compositions of real interest have been considered and no nutrient media has been used to dilute the samples. A measurement set-up has been realized using benchtop instruments for impedance measurements on samples whose bacteria concentration was independently measured by means of standard plate counts. The obtained results clearly indicate that impedance measurement represents a feasible and reliable technique to detect total microbial concentration in ice-cream, suitable to be implemented as an embedded system for industrial machines.

Total Bacterial Count in Soft-Frozen Dairy Products by Impedance Biosensor System

In order to guarantee product safety in the dairy industry, the microbial concentration of food must be ultimately evaluated by means of the standard plate count (SPC) technique, reliable but also slow and difficult to implement in automatic form. On the other hand, detection of bacterial concentration by means of classic impedance microbiology is very attractive due to faster response time (4-14 h versus 24-72 h for the SPC) and easy implementation in industrial machines. Recently, an impedance technique for the detection of bacterial concentration has been introduced that avoids diluting media, thus resulting much simpler to implement in automatic form than existing alternatives. In this paper, various soft-frozen dairy products of different composition and producers have been tested to study the correlation between conventional SPC and such a new impedance technique. It is shown that this later is suitable for real industrial applications.

A Portable Sensor With Disposable Electrodes for Water Bacterial Quality Assessment

Bacterial screening is very important in water environmental monitoring, because the presence of dangerous pathogens can seriously endanger human health. Microbial concentration detection is performed by standard plate count technique, which is reliable but is characterized by long response time and is not suitable to be implemented in automatic form. Based on impedance measurements, this paper presents a portable sensor implemented as an electronic embedded system featuring disposable measurement cells, which is suitable of measuring bacterial concentration in water samples. The system provides a much faster response than standard technique (3–12 h depending on the contamination level versus 24–72 h of the standard technique) and can be used for an in situ microbial test rather than taking samples to a laboratory for analysis. Water samples from different sources (such as rivers, wastewaters, watercourses) are tested using the presented system. Enriched medium is added to the sample to favor bacterial growth. Three different media are tested (Lauria Bertani, Mc Conkey Broth, and Lactose Broth) and data are compared with microbial growth rate and selectivity toward bacterial group (e.g., coliforms). The obtained experimental data show good correlation with the plate count technique.

Effect of feeding a selected combination of galacto-oligosaccharides and a strain of Bifidobacterium pseudocatenulatum on the intestinal microbiota of cats

OBJECTIVE To evaluate the growth kinetics of a strain of Bifidobacterium pseudocatenulatum (BP) on 4 oligo- or polysaccharides and the effect of feeding a selected probiotic-prebiotic combination on intestinal microbiota in cats. ANIMALS 10 healthy adult cats. PROCEDURES Growth kinetics of a strain of cat-origin BP (BP-B82) on fructo-oligosaccharides, galacto-oligosaccharides (GOS), lactitol, or pectins was determined, and the combination of GOS and BP-B82 was selected. Cats received supplemental once-daily feeding of 1% GOS-BP-B82 (10(10) CFUs/d) for 15 days; fecal samples were collected for analysis the day before (day 0) and 1 and 10 days after the feeding period (day 16 and 25, respectively). RESULTS Compared with the prefeeding value, mean fecal ammonia concentration was significantly lower on days 16 and 25 (288 and 281 μmol/g of fecal dry matter [fDM], respectively, vs 353 μmol/g of fDM); fecal acetic acid concentration was higher on day 16 (171 μmol/g of fDM vs 132 μmol/g of fDM). On day 16, fecal concentrations of lactic, n-valeric, and isovaleric acids (3.61, 1.52, and 3.55 μmol/g of fDM, respectively) were significantly lower than on days 0 (5.08, 18.4, and 6.48 μmol/g of fDM, respectively) and 25 (4.24, 17.3, and 6.17 μmol/g of fDM, respectively). A significant increase in fecal bifidobacteria content was observed on days 16 and 25 (7.98 and 7.52 log(10) CFUs/g of fDM, respectively), compared with the prefeeding value (5.63 log(10) CFUs/g of fDM). CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that feeding 1% GOS-BP-B82 combination had some positive effects on the intestinal microbiota in cats.