Browsing by Author "Moutinho, Carla Guimarães"
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- Changes in the pool of free fatty acids in ovine, bovine and caprine milk fats, effected by viable cells and cell-free extracts of Lactococcus lactis and Debaryomyces vanrijiaePublication . Regado, Mafalda A.; Cristóvão, Betina M.; Tavaria, Freni K.; Ferreira, João Paulo; Moutinho, Carla Guimarães; Balcão, Victor; Xavier Malcata, F.Lipolysis catalysed by lipases, native or released by natural microflora in milk, plays a key role in development of aroma and flavour throughout cheese ripening. This research effort was aimed at a deeper understanding of the action of two wild strains used in traditional ewe’s milk cheesemaking in Portugal, viz. Lactococcus lactis and Debaryomyces vanrijiae. They were both tested as viable cells and cell-free extracts – using bovine, ovine and caprine milk fat emulsions as model substrates. Hydrolysis reactions were carried out at 30 and 37 °C, in the case of L. lactis and D. vanrijiae, respectively; the contents of short- and medium-chain fatty acids were determined by high pressure liquid chromatography. Our experimental results showed general trends, viz. preferential depletion of medium chain fatty acids throughout the whole reaction time. However, distinct patterns were observed towards different substrates, depending on the source and form of the biocatalyst at stake.
- Noninvasive methods to determine the critical micelle concentration of some bile acid saltsPublication . Reis, Salette; Moutinho, Carla Guimarães; Matos, Carla; de Castro, Baltazar; Gameiro, Paula; Lima, José L.F.C.In this work the critical micelle concentrations (cmc) of four bile salts, sodium cholate, sodium glycocholate, sodium deoxycholate, and sodium glycodeoxycholate, are determined and presented. Three independent noninvasive methodologies (potentiometry, derivative spectrophotometry, and light scattering) were used for cmc determination, at 25 degrees C with ionic strength adjusted to 0.10 M with NaCl. Spectrophotometric and potentiometric studies of some bile salts were also executed at various ionic strength values, thus allowing the influence of the ionic strength on the cmc value of the bile salt to be assessed. A critical comparison of the cmc values obtained with data collected from the literature is presented. Furthermore, this work makes an evaluation of the conceptual bases of different methodologies commonly used for cmc determination, since variations in the results obtained can be related mainly to different intrinsic features of the methods used (such as sensitivity or the need to include tracers or probes) or to the operational cmc definition applied. The undoubted definition of the experimental bile salt concentration that corresponds to cmc (operational cmc) is essential since in the case of these amphiphiles the formation of micelles is not as abrupt as in the case of ordinary association colloids. The biphasic nature of their aggregation leads to a "round-shaped" variation of the experimental parameters under analysis, which makes difficult the evaluation of the cmc values and can be responsible for the different results obtained.
- β-Blockers and benzodiazepines location in SDS and bile salt micellar systemsPublication . Reis, Salette; Moutinho, Carla Guimarães; Pereira, Eulália; de Castro, Baltazar; Gameiro, Paula; Lima, José L.F.C.The work here described aimed to find out the location of the different species of two families of pharmaceutical substances, namely two beta-blockers (atenolol and nadolol) and two benzodiazepines (midazolam and nitrazepam) in synthetic (sodium dodecyl sulphate, SDS) and natural (bile salts-sodium cholate and sodium deoxycholate) micellar aggregate solutions. Electronic spin resonance spectroscopy studies were carried out, at 25 degrees C and at an ionic strength of 0.10 M in NaCl, using 5-, 12- and 16-doxylstearic acid probes (AS). The immobilization degree of solubilized stearic acid spin probes was found to vary with the position of the nitroxide group in the sequence 5-doxylstearic acid>12-doxylstearic acid>16-doxylstearic acid for SDS and 12-doxylstearic acid>5-doxylstearic acid>16-doxylstearic acid for both bile salts investigated. Therefore, from the rotational correlational time values obtained, it can be inferred that the structure of bile salt micelles is markedly different from that of SDS micelles and the results suggest that the bile salt micelles studied have similar structure independently of differences in the molecular structure of the respective bile salts. Drug location studies were performed at pH 4.0 (SDS solutions) or 7.0 (bile salt solutions) and 10.8 in order to study the effect of the drug ionisation on its relative position on micelles. The results have shown that drug location is controlled by the (i) drug hydrophilicity and acid/base properties, with the more soluble compound in water (atenolol) exhibiting smaller variation of rotational correlational time (in SDS and bile salts solutions), and with both beta-blockers exhibiting smaller deviations in the protonated forms and (ii) the bile salt monomers, with the dihydroxylic bile salt (deoxycholate) producing larger differences. The work described herein allow us to conclude that the (protonated) beta-blockers are probably located on the surface of the detergent micelles, and linked to them by means of essentially electrostatic forces, while the (neutral) benzodiazepines are probably located deeper in the interior of the micelles.