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Biblioteca Digital do IPB (53.442 recursos)

A Biblioteca Digital do IPB, tem por objectivo divulgar e permitir o livre acesso à produção científica produzida pela comunidade académica, promovendo a integração, partilha e a visibilidade da informação científica e garantindo a preservação da memória intelectual do Instituto Politécnico de Bragança.

DTQB - Artigos de Revistas Indexadas ao ISI

Mostrando recursos 1 - 20 de 182

  1. Lignin-based rigid polyurethane foams with improved biodegradation

    Cateto, C.A.; Barreiro, M.F.; Ottati, C.; Lopretti, M.; Rodrigues, A.E.; Belgacem, M.N.
    Rigid polyurethane (RPU) foams have been synthesized using lignin-based polyols obtained by oxypropylation of four distinct lignins (Alcell, Indulin AT, Curan 27-11P, and Sarkanda). Polyol formulations with two lignin/propylene oxide/catalyst content (L/PO/C) ratios were chosen (30/70/2 and 20/80/5). RPU foams have been prepared with a polyol component that incorporates the lignin-based one at contents ranging from 25 to 100%. A 100% commercial polyol-based (Lupranol! 3323) RPU foam was also prepared and used as the reference. RPU foams were characterized in terms of density, compressive modulus, and conductivity. Cell morphology and size estimation were accessed by scanning electron microscopy. Moreover, biodegradation...

  2. Development of chitosan-based antimicrobial leather coatings

    Fernandes, I.P.; Amaral, J.S.; Pinto, V.; Ferreira, M.J.; Barreiro, M.F.
    The development of antimicrobial coatings for footwear components is of great interest both from industry and consumer’s point of view. In this work, antimicrobial leather materials were developed taking advantage of chitosan intrinsic antimicrobial activity and film forming capacity. Considering the specificities of the leather tanning industry, different coating technologies, namely drum, calender and spray, were tested, being the best results achieved with the drum. This last approach was further investigated to assess the effect of chitosan content, type of solubilizing acid, and impregnation time on the achieved antimicrobial capacity. Considering chitosan price (economic reasons) and the obtained results (antimicrobial...

  3. Identification of hare meat by a species-specific marker of mitochondrial origin

    Santos, G.C.; Melo, V. S.; Amaral, J.S.; Estevinho, Leticia M.; Oliveira, M.B.P.P.; Mafra, I.
    Meat species identification in food has gained increasing interest in recent years due to public health, economic and legal concerns. Following the consumer trend towards high quality products, game meat has earned much attention. The aim of the present work was to develop a DNA-based technique able to identify hare meat. Mitochondrial cytochrome b gene was used to design species-specific primers for hare detection. The new primers proved to be highly specific to Lepus species, allowing the detection of 0.01% of hare meat in pork meat by polymerase chain reaction (PCR). A real-time PCR assay with the new intercalating EvaGreen dye was further proposed as a...

  4. Antimicrobial activity of essential oils from mediterranean aromatic plants against several foodborne and spoilage bacteria

    Silva, Nuno; Alves, Sofia; Gonçalves, Alexandre; Amaral, J.S.; Poeta, Patrícia
    The antimicrobial activity of essential oils extracted from a variety of aromatic plants, often used in the Portuguese gastronomy was studied in vitro by the agar diffusion method. The essential oils of thyme, oregano, rosemary, verbena, basil, peppermint, pennyroyal and mint were tested against Gram-positive (Listeria monocytogenes, Clostridium perfringens, Bacillus cereus, Staphylococcus aureus, Enterococcus faecium, Enterococcus faecalis, and Staphylococcus epidermidis) and Gram-negative strains (Salmonella enterica, Escherichia coli, and Pseudomonas aeruginosa). For most essential oils examined, S. aureus, was the most susceptible bacteria, while P. aeruginosa showed, in general, least susceptibility. Among the eight essential oils evaluated, thyme, oregano and pennyroyal oils showed the greatest antimicrobial activity, followed by...

  5. A SYBR green real-time PCR assay to detect and quantify pork meat in processed poultry meat products

    Soares, S.; Amaral, J.S.; Oliveira, M.B.P.P.; Mafra, I.
    Species identification in meat products has grown in interest in recent years since these foodstuffs are susceptible targets for fraudulent labelling. In this work, a real-time PCR approach based on SYBR Green dye was proposed for the quantitative detection of pork meat in processed meat products. For the development of the method, binary meat mixtures containing known amounts of pork meat in poultry meat were used to obtain a normalised calibration model from 0.1 to 25% with high linear correlation and PCR efficiency. The method revealed high specificity by melting curve analysis, being successfully validated through its application to blind meat mixtures, which confirmed its adequacy...

  6. A survey on genetically modified maize in foods commercialised in Portugal

    Fernandes, Telmo J.R.; Amaral, J.S.; Oliveira, M.B.P.P.; Mafra, I.
    Maize, the second most important genetically modified (GM) crop, has the highest number of authorised GM events for food and feed in the EU. To provide consumer’s information, labelling for food products containing more than 0.9% of GM material is demanded by the actual EU legislation. Analysis of foods is then essential to detect and quantify GM maize material and verify the compliance with labelling information. The aim of the present work was to assess the presence of GM maize in a range of processed foods commercialised in Portugal between 2007 and 2010. For this purpose, screening of GM material was carried out by qualitative PCR...

  7. Solubility of hesperetin in mixed solvents

    Ferreira, Olga; Schröder, Bernd; Pinho, Simão
    The study of the solubility of important biomolecules such as flavonoids is essential to support the design of several separation processes in the food and pharmaceutical industries. Following our previous studies, new solubility data of hesperetin in the mixed solvents water + acetone, water + ethanol, and water + methanol were measured, at 298.2 K, by the isothermal shake-flask method. The results obtained show three solid−liquid phase diagrams with distinct features. Additionally, the solid crystals obtained from the solubility studies were analyzed by powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis indicating that, depending on the mixed solvents composition, two different crystal structures of...

  8. Thermal effects on the synthesis of 1,1-dibutoxyethane in a fixed-bed adsorptive reactor

    Graça, N.S.; Pais, L.S.; Silva, V.M.T.M.; Rodrigues, A.E.
    The effects of temperature on the synthesis of 1,1-dibutoxyethane (DBE) in a fixedbed adsorptive reactor were studied by performing both adsorption/desorption and reaction/regeneration experiments at 15 and 35 °C. The Langmuir-type isotherm parameters at 15 and 35 °C were obtained from the adsorption/desorption experiments. The reaction/regeneration experiments showed an increase in both conversion and productivity with increasing temperature. Isothermal and nonisothermal mathematical models were used to simulate the reactor operation with different Damköhler numbers. The simulated results suggest that the reactor productivity can be improved by using the adiabatic operation mode on the fixedbed adsorptive reactor, obtaining a productivity for...

  9. Thermal effects on the synthesis of acetals in a simulated moving bed adsorptive reactor

    Graça, N.S.; Pais, L.S.; Silva, V.M.T.M.; Rodrigues, A.E.
    The effect of temperature on simulated moving bed adsorptive reactor performance was studied by simulation with both isothermal and non-isothermal mathematical models. Simulated results with isothermal mathematical model showed an improvement of SMBR performance criteria and the increase on reaction/separation regions with temperature. It was shown by simulations with non-isothermal mathematical model that the SMBR performance can be also improved by using the adiabatic operation mode. This study of the thermal effects on SMBR operation is an important step for a further implementation of energy integration concepts such as autothermal operation.

  10. Analysis of the synthesis of 1,1-dibutoxyethane in a simulated moving-bed adsorptive reactor

    Graça, N.S.; Pais, L.S.; Silva, V.M.T.M.; Rodrigues, A.E.
    The synthesis of 1,1-dibutoxyethane was carried out in a simulated moving-bed pilot unit LICOSEP 12-26 (Novasep, France) with 12 columns packed with the commercial ion-exchange resin Amberlyst 15(Rohm & Haas, France). Experimentally the best raffinate purity obtained was 85% with a productivity of 5.04 kg L−1 d−1 and a desorbent consumption of 13.5 L kg−1. The TMBR model was used to construct reaction/separation regions and to study the influence of feed composition, switching time, flow rates and mass-transfer resistances on the SMBR performance. The SMBR process shows a potential to be a competitive, efficient and environmentally friendly way to produce...

  11. Separation of nadolol stereoisomers by liquid chromatography : screening of the mobile phase composition

    Ribeiro, António E.; Gomes, P. Sá; Pais, L.S.; Rodrigues, A.E.
    The screening of the most convenient mobile phase composition is presented for the chiral separation of the four stereoisomers of the beta-blocker drug nadolol. When the final goal is the preparative chiral separation, this selection is critical, since solubility, selectivity and retention are all parameters very sensitive with mobile phase composition. Experimental results will show that the best mobile phase composition is, generally, very different if we consider an analytical or a preparative separation point of view.

  12. Solubility of flavonoids in pure solvents

    Ferreira, Olga; Pinho, Simão
    The fast and efficient selection of food-approved solvents is required for a growing number of flavonoids that are continuously being tested for their nutraceutical properties. Solid–liquid equilibrium is an essential source of information for the design of extraction, precipitation, or crystallization processes in the food industry. In this context, the nonrandom two-liquid segment activity coefficient thermodynamic model showed to be an appropriate tool to represent the solubility of several key flavonoids (apigenin, genistein, hesperetin, luteolin) in pure solvents, suggesting its ability to predict solubility in solvents not considered during the correlation procedure. For substances with unknown melting properties the reference...

  13. The influence of structure and surface chemistry of carbon materials on the decomposition of hydrogen peroxide

    Ribeiro, Rui; Silva, Ádrian; Figueiredo, José; Faria, Joaquim; Gomes, Helder
    Carbon materials with different structural and chemical properties, namely activated carbons, carbon xerogels, carbon nanotubes, graphene oxide, graphite and glycerol-based carbon materials, were tested under different operating conditions for their ability to catalyse hydrogen peroxide (H2O2) decomposition in aqueous solutions. Activated carbons treated with concentrated sulphuric acid (ACS) are the most active catalytic materials for H2O2 decomposition in most of the conditions studied, due to the presence of sulphur containing functional groups at their surface. In addition, ACS proved to be a stable catalyst in reutilization tests for H2O2 decomposition. Methanol was used as selective scavenger of hydroxyl radicals (HO...

  14. Removal of 2-nitrophenol by catalytic wet peroxide oxidation using carbon materials with different morphological and chemical properties

    Ribeiro, Rui; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, Helder
    Carbon materials with distinct morphological and chemical characteristics, namely activated carbons,carbon nanotubes, glycerol-based carbon materials and carbon xerogels, were tested for the removal of 2-nitrophenol (2-NP) in aqueous solutions, either by pure adsorption or by catalytic wet peroxideoxidation (CWPO). The results obtained in adsorption experiments carried out at pH 3, T = 323 K, adsorbent load of 0.1 g L−1and 2-NP concentration of 100 mg L−1, show that, in general, the activated carbons have superior adsorption performances compared to the other carbon materials tested, exhibiting removals of 2-NP up to316 mg g−1after 150 min of adsorption.In the CWPO experiments, whilst...

  15. The effects of beating, web forming and sizing on the surface energy of Eucalyptus globulus kraft fibres evaluated by inverse gas chromatography

    Carvalho, M.; Santos, José M.R.C.A.; Martins, A.; Figueiredo, M.
    In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (cs d) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets). The results have shown that the main effect of beating is to increase the fibre’s Lewis acidic character. Web forming caused a strong decrease in cs d and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio...

  16. Polymer blends: the PC-PBT case

    Santos, José M.R.C.A.; Guthrie, J.
    An example of commercially important binary polymer blends is that of PC–PBT composites. The current knowledge of the physical, mechanical and chemical properties of these blends is reviewed and updated in the light of interpretations based on Lewis acid–base intermolecular interactions, as quantified by inverse gas chromatography, carried out under infinite dilution conditions.

  17. Study of a core-shell type impact modifier by inverse gas chromatography

    Santos, José M.R.C.A.; Guthrie, J.
    Inverse gas chromatography (IGC) has been used to study the Lewis acid–base properties of a technologically and commercially important core-shell type elastomer (MBS rubber). The parameters determined were the dispersive component of the surface tension, the surface free energy, the enthalpy and the entropy of adsorption of polar and apolar probes, the surface Lewis acidity constant (Ka), and the surface Lewis basicity constant (Kb). The results show that the MBS rubber is amphoteric but strongly Lewis basic. It is weakly Lewis acidic. The results are in accord with the analysis of the molecular structure of PMMA, the shell component of this impact modifier (IM)....

  18. Characterisation of the surface lewis acid/base properties of the components of pigmented, impact-modified, pc/pbt blends by inverse gas chromatography – phase separation and phase preferences

    Santos, José M.R.C.A.; Guthrie, J.; Fagelman, K.
    Inverse gas chromatography was used to study the surface Lewis acid–base properties of the major components of pigmented, impact-modified, polycarbonate–poly(butylene terephthalate) blends. An investigation of the Lewis acid–base interactions in these polymeric systems has been carried out, based on the values determined for the surface Lewis acidity constant (K ), surface Lewis basicity constant (K ) and on the chemical and physical structure of the materials involved. This a b analysis provided the rationale for an interpretation of the phase separation and the phase preference that exist in these polymer blends, and of the consequences to their physical and mechanical properties.

  19. Characterisation of the surface lewis acid/base properties of poly(butylene terephthalate) by inverse gas chromatography

    Santos, José M.R.C.A.; Guthrie, J.; Fagelman, K.
    The surface of poly(butylene terephthalate) (PBT) was analysed by means of inverse gas chromatography (IGC). The specific component of the adsorption of polar probes on the surface of poly(butylene terephthalate) was found to be endothermic, and the change in the entropy of the system, positive, which is not a common case in IGC. An interpretation is given, based on the contribution of cleavage of hydrogen bonds in the PBT and formation of hydrogen bonds between the probe-molecules and the polymer. The surface Lewis acidity and basicity constants, K and K , respectively, were a b determined and found to correlate well with an analysis of...

  20. Analysis of interactions in multicomponent polymeric systems: the key role of inverse gas chromatography

    Santos, José M.R.C.A.; Guthrie, J.
    The properties of a polymeric system are a consequence of the interactions that occur between the various components of these complex systems. These components may vary significantly in terms of chemical nature (e.g. organic/inorganic), physical properties (e.g. particle size, surface area, molecular weight), structural characteristics and proportion in the formulations composition. This review paper addresses the major approaches in use regarding the analysis of the interactions that occur between the polymeric system components and the use of such approaches in the interpretation of the chemical, physical and thermodynamic properties of these systems. Special attention is given to the technique of inverse gas chromatography. A case study is...

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