Biomedical subjects

José A Teixeira

Publications and source records attributed to José A Teixeira.

10 recordsLinked to original sources

PubMed2006

Isolation and partial characterization of a biosurfactant produced by Streptococcus thermophilus A.

Isolation and characterization of the surface active components from the crude biosurfactant produced by Streptococcus thermophilus A was studied. A fraction rich in glycolipids was obtained by the fractionation of crude biosurfactant using hydrophobic interaction chromatography. Molecular (by Fourier transform infrared spectroscopy) and elemental compositions (by X-ray photoelectron spectroscopy) were determined. Critical micelle concentration achieved was 20 g/l, allowing for a surface tension value of 36 mJ/m(2). Moreover, this glycolipid rich fraction was found to be an anti-adhesive and antimicrobial agent against several bacterial and yeast strains isolated from explanted voice prostheses. Further purification steps should be carefully analyzed as each purification step will increase the costs and decreases the amounts of biosurfactants recovered.

Bacteria↗

PubMed2006

Continuous immobilized yeast reactor system for complete beer fermentation using spent grains and corncobs as carrier materials.

Despite extensive research carried out in the last few decades, continuous beer fermentation has not yet managed to outperform the traditional batch technology. An industrial breakthrough in favour of continuous brewing using immobilized yeast could be expected only on achievement of the following process characteristics: simple design, low investment costs, flexible operation, effective process control and good product quality. The application of cheap carrier materials of by-product origin could significantly lower the investment costs of continuous fermentation systems. This work deals with a complete continuous beer fermentation system consisting of a main fermentation reactor (gas-lift) and a maturation reactor (packed-bed) containing yeast immobilized on spent grains and corncobs, respectively. The suitability of cheap carrier materials for long-term continuous brewing was proved. It was found that by fine tuning of process parameters (residence time, aeration) it was possible to adjust the flavour profile of the final product. Consumers considered the continuously fermented beer to be of a regular quality. Analytical and sensorial profiles of both continuously and batch fermented beers were compared.

Beer↗

PubMed2006

Physicochemical and functional characterization of a biosurfactant produced by Lactococcus lactis 53.

Isolation and identification of key components of the crude biosurfactant produced by Lactococcus lactis 53 was studied. Fractionation was achieved by hydrophobic interaction chromatography which allowed the isolation of a fraction rich in glycoproteins. Molecular (by Fourier transform infrared spectroscopy) and elemental compositions (by X-ray photoelectron spectroscopy) were determined. Critical micelle concentration achieved for the isolated fraction was 14 g/l, allowing for a surface tension value of 36 mJ/m(2). Moreover, the isolated fraction, stable to pH changes between 5 and 9, was found to be an anti-adhesive and antimicrobial agent against several bacterial and yeast strains isolated from explanted voice prostheses, even at low concentrations. Further purification steps should be carefully analyzed as each purification step will increase the costs and decreases the amounts of biosurfactants recovered.

Anti-Infective Agents↗

PubMed2006

New and simple plate test for screening relative transfructosylation activity of fungi.

Several microorganisms are reported to have transfructosylation activity due to fructosyltransferase and/or fructofuranosidase activities. However, the search for other fungi with higher transfructosylation activity remains a challenge. So, a presumptive and indirect colorimetric plate assay for the evaluation of transfructosylation activity in fungi was developed which involved the simultaneous determination in the same plate of glucose and fructose released from sucrose. The method entailed the (a) glucose oxidase-peroxidase coupled reaction using phenol and 4-aminoantipyrine for determination of glucose; and (b) fructose dehydrogenase oxidation in the presence of a tetrazolium salt for determination of fructose. The presence of enzymes with transfructosylation activity was identified by the formation of pink (presence of glucose) and blue (presence of fructose) halos around the fungal colony. In conclusion, the results showed that the method is suitable for screening a large number of fungi due to its simplicity, reproducibility and rapidity and also gives a relative quantitative idea of the transfructosylation activity of different fungi species.

Ampyrone↗

PubMed2005

Relationships between hydrodynamics and rheology of flocculating yeast suspensions in a high-cell-density airlift bioreactor.

In this article a hydrodynamic and rheological analysis of a continuous airlift bioreactor with high-cell-density system is presented. A highly flocculating recombinant strain of Sacharomyces cerevisiae containing genes for lactose transport (lactose permease) and hydrolysis (beta-galactosidase) was exploited to ferment lactose from cheese whey to ethanol. The magnetic particle-tracer method was used to assess the effect of operational conditions (air-flow rate, biomass concentration) on hydrodynamic behavior of an airlift bioreactor during the fermentation process. Measurements of liquid circulation velocity showed the existence of a critical value of biomass concentration at which a dramatic deceleration of net liquid flow appeared with increasing biomass quantity. Rheological analysis revealed exponential increase of viscosity of the yeast floc suspension at the same biomass concentration of about 73 g/dm3 corresponding to 42.8% v/v of solid fraction. These facts have a particular importance for the successful processing of a high-cell-density airlift bioreactor as only a circulated flow regime will be favorable to keep the solid particles in suspension state and evenly distributed throughout the bioreactor.

Bioreactors↗

PubMed2005

Surface properties of Yarrowia lipolytica and their relevance to gamma-decalactone formation from methyl ricinoleate.

The surface of the lipid-degrading yeast, Yarrowia lipolytica, was characterized by contact angle and zeta potential (zeta) measurements. The cells were mainly hydrophilic with a negative charge that was only affected from pH 2 to 4. To study the effects of the surface charges on the biotransformation of methyl ricinoleate into the aroma compound, gamma-decalactone, the zeta values of the substrate droplets were modified by adding a cationic surfactant into the medium at concentrations that did not diminish cell viability: the adhesion of the lipid substrate to the cells was increased but not the overall performance of the process, therefore the adhesion is not the rate limiting here. Our methodology offers interesting perspectives for further applications.

Cetrimonium↗

PubMed2004

Changes in diffusion through the brain extracellular space.

ECS (extracellular space) works as the microenvironment of brain cells. Diffusion through ECS may be described through an effective diffusion coefficient, D (e), which in turn depends on ECS porosity, epsilon, and tortuosity, T. In the present research, diffusion data together with epsilon and T were collected from the specialized literature and analysed to seek a correlation of T versus epsilon. On the basis of D (e) data, upper and lower T boundaries were defined and related to topologically 'dense' and 'loose' cell arrangement. A possible range for T variation was obtained for ECS, with epsilon ranging from 0.05 to 0.6. A tortuosity index ( n ) in the form of T and epsilon logarithmic ratio was introduced. This index may be adopted for recalculation of T or epsilon if only one of these parameters is known. As a result of data analysis and modelling, it was concluded that, upon different external conditions, for instance oxygen depletion, the ECS porosity decreases and cells (presumably through membrane rearrangements) adjust the void space to keep the diffusion within a defined range, which gives the living tissue the ability to maintain the diffusion level up to two or more times higher than in conventional granular bed packing. Thus, even with a dramatic ECS decrease, the cellular system is still able to support a given diffusion by decreasing the value of T. The obtained results clearly show the existence of three data clusters: a region of normal brain functioning, both for young and adult brains, for values of epsilon comprised between 0.15 and 0.30, and two regions of abnormal brain behaviour to the left and to the right of the normal region, corresponding to different states (aging, tumours, anoxia, brain death, etc.). The present approach allows defining the optimal range of epsilon and T to assure the best ECS diffusion efficiency for a specified macromolecule. This might be important in brain clinical treatment.

Animals↗

PubMedDate not supplied

Immobilized particles in gel matrix-type porous media. Nonhomogeneous cell distribution.

The conventional random pore model assumes a homogeneous cell distribution in the gel matrix used to immobilize cells. However, the validity of this model is restricted to values of the exponent alpha, between 1.8 and 2.25, of a model power function relating the diffusivity coefficient in the matrix with the overall cell volume fraction in the system. Based on the analysis of published data for diffusion in gels with immobilized cells and on the homogeneous approach for the random pore model developed in a previous work, a new, nonhomogeneous approach is proposed for alpha values outside the range 1.8-2.25. To explain these data, two main types of nonhomogeneous cell distribution were considered: (1) nonhomogeneous cell distribution in the gel for alpha > 2.25 (type 1) and (2) nonhomogeneity related with anisotropy of cell space orientation when alpha < 1.8 (type 2). In the case of nonhomogeneity of type 1, the cell volume fraction in the layers occupied by cells must be considered in place of the concept previously used for homogeneous distribution, viz., the average cell volume fraction. This model underlines that accumulation of cells in a thin layer close to the surface improves their nutrient intake. For nonhomogeneity of type 2, the tortuosity of such a system is smaller than should be expected if spherical cells were considered, thereby changing the effective diffusion. The model proposed in this work proved to fit into several real cases reported in the literature.

Anisotropy↗

PubMedDate not supplied

Growth model and metabolic activity of brewing yeast biofilm on the surface of spent grains: a biocatalyst for continuous beer fermentation.

In the continuous systems, such as continuous beer fermentation, immobilized cells are kept inside the bioreactor for long periods of time. Thus an important factor in the design and performance of the immobilized yeast reactor is immobilized cell viability and physiology. Both the decreasing specific glucose consumption rate (q(im)) and intracellular redox potential of the cells immobilized to spent grains during continuous cultivation in bubble-column reactor implied alterations in cell physiology. It was hypothesized that the changes of the physiological state of the immobilized brewing yeast were due to the aging process to which the immobilized yeast are exposed in the continuous reactor. The amount of an actively growing fraction (X(im)act) of the total immobilized biomass (X(im)) was subsequently estimated at approximately X(im)act = 0.12 g(IB) g(C)(-1) (IB = dry immobilized biomass, C = dry carrier). A mathematical model of the immobilized yeast biofilm growth on the surface of spent grain particles based on cell deposition (cell-to-carrier adhesion and cell-to-cell attachment), immobilized cell growth, and immobilized biomass detachment (cell outgrowth, biofilm abrasion) was formulated. The concept of the active fraction of immobilized biomass (X(im)act) and the maximum attainable biomass load (X(im)max) was included into the model. Since the average biofilm thickness was estimated at ca. 10 microm, the limitation of the diffusion of substrates inside the yeast biofilm could be neglected. The model successfully predicted the dynamics of the immobilized cell growth, maximum biomass load, free cell growth, and glucose consumption under constant hydrodynamic conditions in a bubble-column reactor. Good agreement between model simulations and experimental data was achieved.

Bacterial Adhesion↗

PubMedDate not supplied

Continuous beer fermentation using immobilized yeast cell bioreactor systems.

Traditional beer fermentation and maturation processes use open fermentation and lager tanks. Although these vessels had previously been considered indispensable, during the past decades they were in many breweries replaced by large production units (cylindroconical tanks). These have proved to be successful, both providing operating advantages and ensuring the quality of the final beer. Another promising contemporary technology, namely, continuous beer fermentation using immobilized brewing yeast, by contrast, has found only a limited number of industrial applications. Continuous fermentation systems based on immobilized cell technology, albeit initially successful, were condemned to failure for several reasons. These include engineering problems (excess biomass and problems with CO(2) removal, optimization of operating conditions, clogging and channeling of the reactor), unbalanced beer flavor (altered cell physiology, cell aging), and unrealized cost advantages (carrier price, complex and unstable operation). However, recent development in reactor design and understanding of immobilized cell physiology, together with application of novel carrier materials, could provide a new stimulus to both research and application of this promising technology.

Beer↗