Browsing by Issue Date, starting with "1998"
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- Interesterification and acidolysis of butterfat with oleic acid by Mucor javanicus lipase: changes in the pool of fatty acid residuesPublication . Balcão, Victor M.; Malcata, F. X.Lipases have become powerful tools in the manufacture of structured fats either via randomization of their glyceride composition or incorporation of externally supplied fatty acid residues in such glycerides. The present communication reports on changes that occurred in the fatty acid pool of anhydrous butterfat subject to interesterification and to acidolysis with oleic acid catalyzed by a commercial lipase immobilized by plain physical adsorption onto hydrophobic hollow fibers at 40°C under controlled water activity. The main goal of this research effort was to engineer butterfat so as to increase its level of unsaturated fatty acid residues and concomitantly decrease its level of medium- and long-chain saturated fatty acid residues (viz. lauric and myristic acids). Although a certain degree of net hydrolysis of butterfat was observed, the triacylglycerols of butterfat subject to acidolysis were found to possess more (approximately 30% w/w) oleic acid and significantly less (8% w/w) lauric acid and less (2% w/w) myristic acid than those of the original butterfat.
- Merging zones standard addition technique for determination of copper in beer by flow injection atomic absorption spectrophotometry.Publication . Fernandes, Sílvia M. V.; Rangel, António O. S. S.; Lima, José L. F. C.A flow injection system for determination of copper in beer by atomic absorption spectrophotometry by the standard additions method is described. The manifold, based on the merging zone technique, prevents the burner head from clogging, as observed with the conventional reference method. With 5 standard additions, results are comparable with those of the reference method. Relative deviations were less than 5.8%, precision was better than 6.4%, and sampling rate was about 30 samples/ h. A less precise, less accurate, but faster procedure (75 samples/h) is possible with only 2 standard additions. The detection limit was 5 micrograms/L.
- Microbiological quality of Portuguese yogurtsPublication . Nogueira, C.; Albano, H.; Gibbs, P.; Teixeira, P.The microbiological quality of four brands of natural yogurts and two probiotic yogurts available in the Portuguese market, was evaluated during the shelf-life period. Although the specific flora decreased during storage it was always within the range of recommended values. No coliforms and an insignificant number of fungi were detected.
- Rapid spectrophotometric determination of nitrates and nitrites in marine aqueous culture mediaPublication . Carvalho, A. P.; Meireles, L. A.; Malcata, F. XavierThe spectrophotometric determination of nitrate in sea water broths for cultivation of, say, microalgae is complicated by the frequent presence of nitrite. Two methods - sulphamic/perchloric acid method (also known as Cawse method) and sulphamic acid method - both claimed to be able to eliminate nitrite interference, were tested using a set of standards, but statistical treatment of the results proved their limitations in nitrate quantification. An improved method, based on former published methods for quantification of nitrite and coupled determination of nitrate and nitrite, was designed and tested. This improved method was compared with the reference method (based on use of a cadmium column) using several standards and biological samples of two culture media for microalgae, in different phases of their growth curve. The results thus obtained have demonstrated that there is no statistically significant difference between them at the 5% level. The precision of the method was tested by repeating determinations with three sets of standard mixtures containing nitrate and nitrite. The method proposed has advantages over conventional methods in reduced time of analysis, as well as high precision and accuracy, so it may be a good alternative for determination of nitrite and nitrate in marine aqueous media.
- Viability of bifidobacterium la ctis and lactobacill us acidophilus in milk: sodium chloride concentration and storage temperaturePublication . Gomes, Ana M. P.; Teixeira, M. G. M.; Malcata, F. XavierThe growth and viability of Bifidobacterium lactis and Lactobacillus acidophilus per se and for both strains as a coculture were studied in reconstituted skim milk so as to assess their dependence upon temperature (5, I0 and 15C), NaCl concentration (0, 0.51 and 1.03 mol L-'), and storage time (0–8 weeks). Cultures of B. lads exhibited no signijkant loss of viability either with increasing NaCl concentration or increasing storage temperature within the ranges studied On the other hand, viability of L. acidophilus decreased with increasing temperature and increasing NaCl concentration under similar conditions. When cocultured with L. acidophilus, B. lactis was signiJicantly less tolerant to higher NaCl levels and higher temperatures than when in pure culture, although rial numbers were still above the threshold required for commercial application. Coculturing with B. lactis had no detrimental effect on viability of L. acidophilus. A mechanistic model, which considers the behavior of the pure and mixed microbial populations is described by specijic death rates which vary with temperature following Arrhenius relationships) and NaCl levels following simple inhibition kinetics) in the milk medium. Activation energies for the death rates of B. lactis and L. acidophilus were 14 kcal mot' and 9–15 kcal mol-I, respectively.
- Potencial biotecnológico das microalgasPublication . Carvalho, A. P.; Meireles, L. A.; Malcata, F. X.; Oliveira, G.; Raposo, M. F.; Morais, R.
- Effects of different ripening procedures on the final characteristicsPublication . Freitas, A. C.; Malcata, F. X.Picante da Beira Baixa (or Picante) cheese is a hard, piquant, salted traditional cheese manufactured in Portugal from raw sheep’s and goat’s milks. The purpose of this work was to quantitatively assess the influence of various ripening procedures on the final characteristics of Picante cheese. Two alternative ripening protocols were considered, the traditional one and another with controlled environmental conditions via use of maturation chambers set at different preselected temperatures. The experimental cheeses were characterised in terms of microbiological, physicochemical, biochemical, sensorial and textural properties. Ripening time and temperature were statistically significant parameters for all microflora. The two ripening methods led to statistically significant differences in all physicochemical and biochemical parameters, especially the moisture content and the soluble nitrogen fractions (i.e. water loss was slower and proteolysis was faster in cheeses ripened via the traditional method). Differences in microbiological, physicochemical and biochemical properties were probables implicated in differences in textural and sensorial properties, especially cheese hardness and flavour. It was concluded that the standard ripening method was closest to the traditional one in terms of final cheese characteristics when the ripening temperature was above 11.5 7C.
- O Infante D. Fernando de Portugal, senhor de Serpa (1218-1246): história da vida e da morte de um cavaleiro andantePublication . Pereira, Armando de SousaDurante a primeira metade do século XIII vive-se em Portugal um ambiente de crise, que atinge o seu auge no reinado de Sancho II e na guerra civil que lhe sucedeu, imagem das profundas mutações económicas, sociais e políticas ocorridas num país ainda em construção territorial. Este cenário é aqui percorrido numa perspectiva individual, a do infante D. Fernando, filho do rei Afonso II e senhor da terra de Serpa, que desempenhou papel activo naqueles acontecimentos; estabelecem-se o itinerário e as singularidades do seu percurso, interpretam-se as suas atitudes e os comportamentos que manifestou perante as realidades que então se viviam, e que fazem dele um autêntico cavaleiro andante.
- Sequential determination of titratable acidity and tartaric acid in wines by flow injection spectrophotometryPublication . Rangel, António O. S. S.; Tóth, Ildikó V.A flow injection manifold is proposed for the sequential determination of titratable (total) acidity based on a pseudotitration and of tartaric acid based on the formation of a coloured vanadate complex. The method involves in-line dialysis prior to injection to avoid interference from the sample background absorption in the spectrophotometric detection. The changes in the colour of both reactions were monitored using two flow cells aligned in the optical path of a single spectrophotometer. Wine samples were analysed without any sample pre-treatment; table wines in the range 1–10 g l21 (total acidity) and 0.5–4 g l21 (tartaric acid) and port wines in the range 1–8 g l21 (total acidity) and 0.5–5 g l21 (tartaric acid). Sixteen samples can be measured per hour, and the results were comparable to those obtained by reference procedures for both determinations. RSDs (n = 10) generally lower than 3% were obtained