CBQF - Contribuições em Revistas Científicas / Contribution to Journals
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- Rheological properties of high-methoxyl pectin and locust bean gum solutions in steady shearPublication . Silva, J. A.Lopes da; Gonçalves, M. P.; Rao, M. A.The Cross and Carreau flow models described well the shear rate-apparent viscosity data. The coil overlap parameter, c[η], correlated well with the zero-shear rate specific viscosities of these mixtures. Experimental values of intrinsic viscosities of the mixtures were in good agreement with the prediction based on an additive model of the individual contributions of the gums. From the results obtained for the mixtures of both polysaccharide solutions at similar viscosity, pH and ionic strength, no significant interactions were detected. Hypotheses for this lack of polymer interaction were developed. Results with such model systems are useful in understanding the relation of composition to the properties of complex food systems.
- Inducible thermotolerance in Lactobacillus bulgaricusPublication . Teixeira, P.; Castro, H.; Kirby, R.The effect of a sublethal heat challenge on the subsequent thermotolerance of Lactobacillus bulgaricus at different stages of growth was investigated along with the effect of heating menstrum on survival. The response of the cells to heat stress was shown to be dependent upon both cell age and heating menstrum. Heat-inducible thermotolerance could be provoked in cells which had been growing exponentially when they were subjected to the sublethal heat stress: pre-incubation at 10°C above the optimum growth temperature. The same effect could not, however, be reproduced in cells taken from the stationary phase. Cells from the stationary phase were shown to always be more thermotolerant as compared to exponential phase cells. Cells showed a greater thermotolerance when heated in milk as compared to buffer.
- Mathematical design of continuous, isothermal crystallizers with homogeneous nucleation: a simplified approachPublication . Malcata, F. XavierA simplified, systematic approach to the mathematical simulation of crystallizers is attempted by using the fundamental principles of mass conservation, via a population balance to the solid phase and a solute balance to both solid and liquid phases. A continuous, isothermal and isochoric crystallizer is assumed to be described by the MSMPR model under transient operating conditions with complete micromixing. The birth and death functions are assumed nil. Homogeneous nucleation is considered at a rate which is independent of the solution supersaturation. The growth rate of the crystals is described by McCabe's law. The possibility of solving the population balance and the mass balance independently is explored, and the conditions of validity for such an approach are found. The maximum linear dimension of crystal and the liquor concentration profile as functions of time are obtained. The approximation is found to be generally good for a period of time right after start-up of the crystallizer. A much wider range of time ensuring a satisfactory approximation is possible provided that the system and operation-dependent parameter takes small values.
- Effect of time and temperature of fermentation on the microflora of grape pomacePublication . Silva, M. L.; Malcata, F. X.The effects of fermentation time and temperature of grape pomace on the number of bacteria and yeasts were assessed using ANOVA of experimentally generated data, as well as analysis of models derived from first principles and fitted by non-linear regression to such data. Specific rates of death of yeasts and bacteria were experimentally obtained at different fermentation times (pilot scale), and at different fermentation times and different temperatures (laboratory scale) for pomace of Alvarinho and Loureiro grape varieties obtained after vinification at two different locations. Viable numbers of yeasts and bacteria in grape pomace were high, especially in the first 3 week of fermentation; for bacteria, there was an increase of their levels during the first 3 week, followed by a significant decrease towards 9 week; for yeasts there was a monotonic decrease throughout such whole period. The numbers of viable microorganisms were mathematically correlated with time and temperature for both wineries using mechanistic models and following a methodology of increasing model complexity. After having checked the validity of underlying assumptions of normal distribution and constant variance of residuals of the experimental data, determination of the best nested model was based on an F-test; such model considered that the behavior of the microbial population is well described by a constant specific growth rate and an increasing specific death rate, both of which vary with temperature following Arrhenius relationships. Activation energies for the specific death rates of yeasts and bacteria were (1.469-1.560) × 104 and (2.584-4.152) × 104 cal/mol, respectively, for the temperature range 20-35 °C. Prediction of the time profile of viable numbers of the major families in the adventitious microflora of grape pomace, as a function of fermentation parameters that are easily manipulated is important in attempts to eventually standardize this solid-state.
- Os bens comuns e o bem comumPublication . Silva, Margarida
- Survival of probiotic bacteria in a whey cheese vector submitted to environmental conditions prevailing in the gastrointestinal tractPublication . Madureira, A. R.; Pereira, C. I.; Truszkowska, K.; Gomes, Ana M. P.; Pintado, M. E.; Malcata, F. X.Various foods may be used to deliver probiotic bacteria into the gastrointestinal tract; one such example is Requeijão, a Portuguese whey cheese. Survival and stability of Bifidobacterium animalis strains BLC-1, Bb-12, and Bo, Lactobacillus acidophilus strains LAC-1 and Ki, L. paracasei ssp. paracasei strain LCS-1 and L. brevis strain LMG 6906 inoculated into Requeijão, when exposed to simulated gastrointestinal tract conditions, were assessed. Homogenates of inoculated whey cheese in 0.85% (w/v) sterile saline water were exposed to a solution of hydrochloric acid (pH 2.5–3.0) and pepsin (1000 unitsmL–1) at 371C, and then to 0.3% (w/v) bile salts after 60 or 120 min of acid exposure. All bacterial strains retained their initial viable cell numbers. Bifidobacterium animalis strains Bb-12 and Bo, and L. brevis strain LMG 6906 exhibited the highest viable cell numbers when exposed to bile salts, whereas the other strains had variable death rates.
- Incidence of Listeria spp. in domestic refrigerators in PortugalPublication . Azevedo, Inês; Regalo, Mafalda; Mena, Cristina; Almeida, Gonçalo; Carneiro, Luísa; Teixeira, Paula; Hogg, Tim; Gibbs, Paul A.The main objectives of this study were to determine the incidence of Listeria spp. in Portuguese domestic refrigerators and to evaluate some of the hygienic practices in the domestic environment that might contribute to the persistence of the organisms. It was found that L. monocytogenes was present in 3 domestic refrigerators of the 86 investigated. L. grayi and L. innocua were also isolated from 4 and 1 refrigerators, respectively. Overall, the information obtained from our survey demonstrates the need for consumer education in Portugal regarding safe food handling practices. For the refrigerators investigated, ≈71% were operating at a temperature higher than 6.1ºC, 87% were cleaned only monthly or less frequently, and only 8% were cleaned with appropriate proprietary cleaning products available in supermarkets.
- Turbidimetric and nephelometric flow analysis: concepts and applicationsPublication . Morais, Inês P. A.; Tóth, Ildikó V.; Rangel, António O. S. S.A review on flow analysis with turbidimetric and nephelometric detection is presented. A brief discussion of the principles of turbidimetry and nephelometry is given. Particular emphasis is devoted to coupling different flow techniques (flow injection, sequential injection, multicommutation) to these detection techniques. Applications in environmental, pharmaceutical, biological, and food samples are summarized and compared in terms of application range, flow configuration, repeatability, and sampling rate.
- Infusions of Portuguese medicinal plants: dependence of final antioxidant capacity and phenol content on extraction featuresPublication . Gião, Maria S.; González-Sanjosé, Maria L.; Rivero-Pére, Maria D.; Pereira, Cláudia I.; Pintado, Manuela E.; Malcata, F. XavierBACKGROUND: Aqueous extracts of most medicinal plants traditionally employed in Portugal (at the ratio of 1 g plant: 110mL water) have been assayed for total antioxidant capacity and phenol content, in order to elucidate their claimed medicinal features. RESULTS: The antioxidant activity was assessed by theABTS•+ method; the ascorbic acid equivalent values ranged from 1.4280 ± 0.1261 g L−1 for avocado (Persea americana (Lauraceae)) obtained by infusion of powder, down to 0.0027 ± 0.0012 g L−1 for olive (Olea europaea (Oleaceae)) obtained by infusion of leaves. Total phenol content was determined by the Folin–Ciocalteu procedure; the gallic acid equivalent values ranged from 0.5541 ± 0.0289 g L−1 for avocado obtained by infusion of powder, down to 0.0053 ± 0.0014 g L−1 for olive obtained by boiling leaves. A good correlation between total antioxidant capacity and total phenol content was found. CONCLUSION: The method of powder infusion should be chosen if high concentration of antioxidants are sought. On the other hand, a high antioxidant capacity and a high phenol content correlate well with the empirically established (and widely publicised) capacity to treat respiratory infections.