Percorrer por autor "Guedes, A. Catarina"
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- Attempts to identify natural antioxidants bearing DNA protection features, produced by scenedesmus ObliquusPublication . Guedes, A. Catarina; Amaro, Helena M.; Pereira, Ricardo D.; Seabra, Rui; Tamagnini, Paula; Moradas-Ferreira, Pedro; Malcata, F. Xavier
- Evaluation of the antioxidant activity of cell extracts from microalgaePublication . Guedes, A. Catarina; Gião, Maria S.; Seabra, Rui; Ferreira, Antonio; Tamagnini, Paula; Moradas-Ferreira, Pedro; Malcata, F. XavierA growing market for novel antioxidants obtained from non-expensive sources justifies educated screening of microalgae for their potential antioxidant features. Characterization of the antioxidant profile of 18 species of cyanobacteria (prokaryotic microalgae) and 23 species of (eukaryotic) microalgae is accordingly reported in this paper. The total antioxidant capacity, accounted for by both water- and lipid-soluble antioxidants, was evaluated by the (radical cation) ABTS method. For complementary characterization of cell extracts, a deoxyribose assay was carried out, as well as a bacteriophage P22/Salmonella-mediated approach. The microalga Scenedesmus obliquus strain M2-1 exhibited the highest (p > 0.05) total antioxidant capacity (149 ± 47 AAU) of intracellular extracts. Its scavenger activity correlated well with its protective effects against DNA oxidative damage induced by copper(II)-ascorbic acid; and against decay in bacteriophage infection capacity induced by H2O2. Finally, performance of an Ames test revealed no mutagenic effects of the said extract.
- Increase of the yields of eicosapentaenoic and docosahexaenoic acids by the microalga Pavlova lutheri following random mutagenesisPublication . Meireles, Luís A.; Guedes, A. Catarina; Malcata, F. XavierThe high commercial values of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids have driven a strain-improvement program, aimed at increasing the content of those fatty acids in the microalga Pavlova lutheri (SMBA 60) as parent strain. After a round of mutation using UV-light as mutagenic agent, an isolate strain (tentatively called II#2) was obtained, the EPA and DHA contents of which (in % dry biomass) were 32.8% and 32.9% higher than those of the control, native strain. The final EPA yields, when the cultures were maintained under appropriate conditions, were 17.4 and 23.1 mg · g−1 dry biomass, for the wild-type and the II#2 strain, respectively, whereas the final DHA yields were 8.0 and 10.6 mg · g−1 dry biomass, respectively. These results suggest that random mutagenesis can successfully be applied to increase the yield of n-3 fatty acids by microalgae.
- Lipid class composition of the microalga Pavlova Lutheri: Eicosapentaenoic and docosahexaenoic acidsPublication . Meireles, Luís A.; Guedes, A. Catarina; Malcata, F. XavierThe lipid classes of Pavlova lutheri, cultivated in semicontinuous mode, were studied by thin-layer chromatography and gas chromatography in attempts to describe the distribution of fatty acid residues within its lipid pool, with special emphasis on eicosapentaenoic (C20:5n−3, EPA) and docosahexaenoic (C22:6n−3, DHA) acids. Neutral lipids and glycolipids were the major constituents and accounted for 57 and 24% of the total fatty acid residues (TFA), respectively. Phospholipids accounted for 10% of TFA. Two lipid classes, acylated steryl glycosides (SG) and diphosphatidylglycerols (DPG), were eventually identified in P. lutheri for the first time. The nonpolar fraction was mainly composed of triacylglycerol (TAG), whereas the polar fraction was mainly composed of monogalactosylacylglycerols (MGDG). The distribution of total EPA and DHA within the lipid pool was calculated in attempts to ascertain the quality of said microalgae as a feed source, as well as the possibility of enhancement of individual fatty acid production and extraction thereafter. EPA was especially concentrated in MGDG (45%) and TAG (33%); conversely, DHA was dispersed through various classes, especially within TAG (27%), DPG (22%), and betaine lipids (21%).
- On-line control of light intensity in a microalgal bioreactor using a novel automatic systemPublication . Meireles, Luís A.; Guedes, A. Catarina; Barbosa, Catarina R.; Azevedo, José L.; Cunha, João P.; Malcata, F. XavierThe influence of light intensity upon biomass and fatty acid productivity by the microalga Pavlova lutheri was experimentally studied using a novel device. This device was designed to automatically adjust light intensity in a photobioreactor: it takes on-line measurements of biomass concentration, and was successfully tested to implement a feedback control of light based on the growth rate variation. Using said device, batch and semicontinuous cultures of P. lutheri were maintained at maximum growth rates and biomass productivities – hence avoiding photoinhibition, and consequent waste of radiant energy. Several cultures were run with said device, and their performances were compared with those of control cultures submitted to constant light intensity; the biomass levels attained, as well as the yields of eicosapentaenoic and docosahexaenoic acids were calculated – and were consistently higher than those of their uncontrolled counterpart.
- Supercritical fluid extraction of carotenoids and chlorophylls a, b and c, from a wild strain of Scenedesmus obliquus for use in food processingPublication . Guedes, A. Catarina; Gião, Maria S.; Matias, Ana A.; Nunes, Ana V. M.; Pintado, Manuela E.; Duarte, Catarina M. M.; Malcata, F. XavierFaster and more selective extraction methods are urged to recover food-grade pigments and antioxidants from microalgae - which do not resort to food-incompatible and environment-unfriendly solvents. Hence, this study ascertained the influence of pressure, temperature, CO2 flow rate and a polar co-solvent upon the yields of carotenoids and chlorophylls in supercritical fluid extraction of Scenedesmus obliquus biomass. The highest carotenoid yield was attained at 250 bar and 60 degrees C. The yields of chlorophylls, when using plain CO2, increased slightly with pressure, but decreased with temperature and CO2 flow rate; the highest yield of chlorophyll a was at 4.3 g(CO2), min(-1), whereas ethanol as co-solvent increased all yields except that of chlorophyll c. The highest ratio of total carotenoids to chlorophyll a was reached at 250 bar and 60 degrees C. A remarkable selectivity was observed under these operating conditions, which may enable easy separation and purification of the aforementioned pigments.