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- 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.
- Potencial biotecnológico das microalgasPublication . Carvalho, A. P.; Meireles, L. A.; Malcata, F. X.; Oliveira, G.; Raposo, M. F.; Morais, R.
- Antimicrobial activity and lipid profile of seaweed extracts from the North Portuguese coastPublication . Mendes, M.; Pereira, R.; Pinto, I. Sousa; Carvalho, A. P.; Gomes, A. M.Seaweeds or marine macroalgae are a potential renewable resource in the marine environment and can represent a source of new natural compounds for human nutrition. This experimental work focused on the selection of a suitable extraction method, using Gracilaria vermiculophylla as a model, followed by the characterization of the antimicrobial activity of different solvent extracts of Gracilaria vermiculophylla, Porphyra dioica and Chondrus crispus, both from wild and from an integrated multi-trophic aquaculture system (IMTA), collected in the north of Portugal. Additionally, the fatty acid profile of the seaweed extracts was also investigated. Extraction tests included the definition of the physical state of the seaweed, temperature and type of solvents to be used during the process. Results revealed that test organisms (Gram negative and Gram positive bacteria as well as one yeast species) were more sensitive to extracts obtained with dried algae, processed continuously at higher temperatures. Results from antimicrobial activity of wild and IMTA seaweed extracts showed stronger antimicrobial activity in extracts of ethyl acetate when compared with those from methanol and diethyl ether; furthermore, among the type of microorganisms tested, there was tendency for inhibition of the Gram positive ones. In general, there appears to be a higher antimicrobial activity for the microorganisms under study in extracts obtained from aquaculture species, when compared with the wild ones. The fatty acid profile of ethyl acetate extracts revealed a predominance of saturated fatty acids (SFA), especially palmitic acid (16:0), followed by polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA). A higher content of fatty acids in aquaculture extracts of Gracilaria vermiculophylla and Porphyra dioica was also observed.
- Hollow fibre modules for CO2 transfer in microalgal culturesPublication . Carvalho, Ana P.; Malcata, F. Xavier
- Potential valorisation of vinification by-productsPublication . Santos, A. F.; Ferraro, V.; Cruz, I. B.; Ferreira Jorge, R.; Carvalho, A. P.; Castro, P. M. L.; Pintado, M. E.
- w-3 fatty acids as functional ingredients: past and futurePublication . Carvalho, Ana P.; Malcata, F. Xavier
- Nutritional characterization of acorn flour (a traditional component of the Mediterranean gastronomical folklore)Publication . Silva, Sara; Costa, Eduardo M.; Borges, André; Carvalho, Ana Paula; Monteiro, Maria João; Pintado, M. E.Abstract Nowadays, acorns, the fruits of Quercus trees, are mostly associated with animal feed. However they are part of the traditional gastronomical folklore of severalMediterranean countries. Though several uses can be mentioned, one of the most common uses is powdering the acorns in order to produce a flour that can substitute regular corn flour in the manufacture breads and cakes. An example of this is acorn bread, a typical Portuguese loaf.However, to the best of our knowledge, there is no information about the nutritional value of these flours. As such, the main goal of this work was to describe the nutritional value of acorn flours from two different subspecies of Quercus abundant in Portugal (Quercus ilex and Quercus rotundifolia) obtained using two different traditional methods (drying and roasting). The results demonstrated that all flours possessed interesting nutritional properties, namely the absence of gluten and elevated values of both monounsaturated and polyunsaturated fatty acids. Because of these facts and it’s low production cost, acorn flour poses as an interesting alternative to traditional flours particularly for gluten intolerant individuals.
- Response surface evaluation of microwave-assisted extraction conditions for Lycium barbarum bioactive compoundsPublication . Mendes, Marta; Carvalho, Ana P.; Magalhães, Júlia M. C. S.; Moreira, Manuela; Guido, Luís; Gomes, Ana M. P.; Delerue-Matos, CristinaThe effects of microwave-assisted extraction (MAE) on the qualitative and quantitative composition of extracted bioactive phytochemicals are strongly dependent on specific operational conditions. The impact of temperature, extraction time, and solvent dielectric properties on theMAE of antioxidant compounds fromgoji berry is hereby reported and discussed. Results were evaluated in terms of antioxidant capacity (ascertained by ABTS and ORAC assays), complemented with quantification of total phenolics content (TPC), and characterization of extracts through HPLC. Furthermore, the effect of storage temperature was also studied. Results revealed that temperature and solvent properties exert a significant effect on TPC and ORAC assays, whereas irradiation time plays a key role in the preparation of extracts to be evaluated through ABTS. The effect of solvent properties is tentatively explained considering the dielectric properties ofmethanol andwater,whereas the observed effect of temperature could be explained by its influence on the solubility of phenolic compounds. Industrial Relevance: A careful selection of operational conditions duringMAE, designed for a specific antioxidant assay, allows an increase in the bioactivity of the resultant extracts,which may become important in terms of industrial applications.
- Polyunsaturated fatty acids as ingredients for functional foodsPublication . Carvalho, Ana P.; Malcata, F. Xavier
- Transfer of carbon dioxide within cultures of microalgae: plain bubbling versus hollow-fiber modulesPublication . Carvalho, Ana P.; Malcata, F. XavierIn attempts to improve the metabolic efficiency in closed photosynthetic reactors, availability of light and CO2 are often considered as limiting factors, as they are difficult to control in a culture. The carbon source is usually provided via bubbling of CO2- enriched air into the culture medium; however, this procedure is not particularly effective in terms of mass transfer. Besides, it leads to considerable waste of that gas to the open atmosphere, which adds to operation costs. Increase in the interfacial area of contact available for gas exchange via use of membranes might be a useful alternative; microporous membranes, in hollow-fiber form, were tested accordingly. Two hollow-fiber modules, different in both hydrophilicity and outer surface area, were tested and duly compared, in terms of mass transfer, versus traditional plain bubbling. Overall volumetric coefficients (KLa) for CO2 transfer were 1.48 10-2 min-1 for the hydrophobic membrane, 1.33 10-2 min-1 for the hydrophilic membrane, and 7.0 10-3 min-1 for plain bubbling. A model microalga, viz. Nannochloropsis sp., was cultivated using the two aforementioned membrane systems and plain bubbling. The produced data showed slight (but hardly significant) increases in biomass productivity when the hollow-fiber devices were used. However, hollow-fiber modules allow recirculation of unused CO2, thus reducing feedstock costs. Furthermore, such indirect way of supplying CO2 offers the additional possibility for use of lower gas pressures, as no need to counterbalance hydrostatic heads exists.