Browsing by Author "Malcata, F. Xavier"
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- Action of cardosin A from Cynara humilis on ovine and caprine caseinatesPublication . Silva, Sofia V.; Malcata, F. XavierIn the Iberian Peninsula, the proteinases present in the flowers of members of the Cynara genus, C. cardunculus, C. humilis and C. scolymus, have for many years been successfully used in the manufacture of traditional cheeses from ovine and/or caprine milk on individual farms (Vieira de Sá & Barbosa, 1972; Trujillo et al. 1994). In Portugal, C. cardunculus is the species most frequently employed. Although commercial thistle was tentatively assumed to be pure in taxonomic terms, accurate analyses have shown that the flowers of C. cardunculus are often mixed with flowers of C. humilis (Pires et al. 1994). The clotting activity of C. humilis is due to an aspartic proteinase, currently designated cardosin A and similar to another enzyme obtained from C. cardunculus. This enzyme is similar in specificity and activity to chymosin (Pires et al. 1994). The action of cardosin A from C. cardunculus upon ovine and caprine caseins has been reported recently (Ramalho-Santos et al. 1996; Simo4es, 1998; Sousa & Malcata, 1998), but as yet there is no information on the proteolytic activity of the proteinase from C. humilis upon caseins from milks other than bovine. Caseins from small ruminants' milks are the usual substrates of cardosin during milk coagulation and cheese ripening, and sodium caseinate represents an intermediate system between isolated caseins and the cheese matrix that is free from interference by fat. Thus ovine and caprine caseinates may be useful substrates for investigating the proteolytic activity of cardosin. The aim of the present study was to compare the action of pure cardosin A, obtained from C. humilis, on caprine and ovine caseinates, and to assess the in vitro contribution of this enzyme to the overall proteolytic action of thistle rennet.
- Adsorption of protein from several commercial lipase preparations onto a hollow-fiber membrane modulePublication . Balcão, Vitor M.; Vieira, Madalena C.; Malcata, F. XavierTen commercially available crude preparations of lipase from various microbial sources were adsorbed from aqueous buffers at several initial concentrations onto a bundle of hydrophobic hollow fibers made of poly(propylene) at pH 7.0 and 40 °C. The kinetics of adsorption were evaluated from measurements at various times of the protein content of the supernatant solution (using BSA as equivalent) in a well-mixed reservoir placed in series with the hollow fiber module. Preliminary tracer experiments have indicated that the module and the tank can be simulated as a system consisting of a plug flow reactor in series with a continuous stirred tank reactor. A mechanistic model based on the hydrodynamic assumptions associated with this system coupled with the postulation of two reversible first-order steps for the adsorption of protein was successfully fitted to the experimental data via nonlinear regression analysis. The statistical significance of the model was checked using tests for lack of fit. This work is useful in predicting the time period required to immobilize a (crude) lipase by adsorption onto a hydrophobic hollow fiber module, a configuration which has proved successful in the recent past for the performance of lipase-catalyzed reactions.
- Advances in the role of a plant coagulant (Cynara cardunculus) in vitro and during ripening of cheeses from several milk speciesPublication . Sousa, Maria José; Malcata, F. XavierExtracts from dried flowers of Cynara cardunculus have been employed successfully for many centuries in Portugal and some regions of Spain for the manufacture of traditional cheeses. Several studies have been performed in vitro and in actual cheeses focusing on the activity and specificity of proteinases from C. cardunculus, in attempts to further characterise this plant coagulant as a proteolytic agent in cheese ripening. In vitro studies encompassed extraction conditions, storage of extracts, proteolysis and specificity on caseins using experimental conditions that parallel milk and cheese during ripening. In vivo studies encompassed the effect of the type of milk (bovine, ovine and caprine) in terms of proteolysis, specificity of those plant proteinases during ripening, comparison of microbiological, chemical, proteolytic and lipolytic characteristics in ovine milk cheeses relative to animal rennet counterparts, and effect of native microflora, thermal processing and addition of starter cultures in ovine cheeses
- A água e a nutrição-veículo deinteracção com o HomemPublication . Vasconcelos, Marta W.; Malcata, F. Xavier
- A água e os alimentos: componente activo e passivoPublication . Carvalho, Ana P.; Malcata, F. XavierA água é o componente mais abundante dos alimentos - contribuindo, de modo decisivo, para algumas das características desejáveis dos mesmos, em termos nutricionais, organolépticos e funcionais, mas igualmente para a sua perecibilidade intrínseca. Com efeito, a água determina a velocidade a que as reacções químicas ocorrem no alimento, controla a taxa de crescimento microbiano no seio do mesmo, e desempenha um papel crítico na sua textura. Está igualmente associada a componentes hidrofóbicos e hidrofílicos do alimento - de um modo tão complexo que, se tais relações forem perturbadas de forma substancial (tal como acontece durante a secagem ou a congelação), afigura-se como frequentemente impossível repor o estado original. Graças aos seus efeitos e funções, a água é por isso essencial aos, e nos, alimentos.
- Alternative cheesemaking methods with raw ewes’ milk – microbiological, chemical, textural and sensory characteristicsPublication . Reis, Patrícia J. M.; Tavaria, Freni K.; Malcata, F. XavierSerra da Estrela cheese was manufactured using a novel, customised apparatus – designed to meet the specialty cheese’s specifications, and the resulting product was compared with that obtained via traditional manufacture in the same dairy. Semiindustrial cheesemaking led to a significantly (p<0.05) higher fat content in the final cheeses, with favourable consequences in terms of flavour and consumer acceptability – and significantly (p<0.05) lower viable numbers of (unwanted) enterococci in the matured cheese. Textural characteristics were broadly similar. Proteolysis was significantly (p<0.05) faster, but it was more variable in artisanal than in semi-industrial cheeses. The latter received significantly (p<0.05) better scores for texture, but lower scores for flavour. However, both products were within the specifications set forth by national regulations pertaining to Serra da Estrela PDO cheeses, so the novel apparatus is rather promising towards improved small-scale cheesemaking.
- Alternative formulation of the problem of mass transfer during bubble formation in the presence of an interfacial chemical reactionPublication . Malcata, F. XavierThe removal of a dilute solute from a gas mixture being injected through a submerged single nozzle with an instantaneous chemical reaction occurring on the gas/liquid interface is theoretically studied. An improved version of the double surface-renewal model for the molecular transport of solute is reported. The reasoning underlying this improvement arises from the decoupling of the bulk and overall concentration of solute in the bubble, and requires an extra parameter for full description. An analytical formula pertaining to the overall depletion of solute by reaction with time is obtained. Simplifications of this result are presented and discussed f or asymptotic behaviors. The propriety of the analysis for the modeling of experimental evidence is included.
- Amino acid and soluble nitrogen evolution throughout ripening of Serra da Estrela cheesePublication . Tavaria, Freni K.; Franco, Inmaculada; Carballo, F. Javier; Malcata, F. XavierFour batches of Serra da Estrela cheese originating from as many dairy farms were sampled throughout the ripening period, and assayed for the evolution of free amino acid (FAA) content, total nitrogen content (TN), water-soluble nitrogen content (WSN), trichloroacetic acid-soluble nitrogen content (TCASN) and phosphotungstic acid-soluble nitrogen content (PTASN). The WSN content increased from 1% (on the day of manufacture) up to 43% of TN by 180 d of ripening, thus reflecting the intense proteolytic activity of the enzymes contributed by the plant coagulant utilized. The TCASN was also found to be high in this cheese by the end of ripening (16–20%), which suggests a high extent of FAA release throughout maturation. The major FAA by 180 d of ripening were Glu, Val, Leu and Lys, representing 56–70% of the total in all four dairies sampled. Cheeses produced from refrigerated milk possessed higher amounts of g-amino-n-butyric acid (Gaba) and lower amounts of Glu when compared with those manufactured withnon-refrigerated milk.
- An approach to effluent bioremediation: cadmium removal by Desmodesmus pleiomorphusPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. Xavier
- An important source of coagulating enzymes for cheesemaking: uses of Cynara cardunculus L.Publication . Malcata, F. Xavier; Silva, Sofia V.