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Torres D.P.M.,Biotempo Biotechnology Consulting Ltd. Spinpark | Torres D.P.M.,IBB Institute for Biotechnology And Bioengineering | Torres D.P.M.,University of Porto | Bastos M.,CIQ UP | And 4 more authors.
Carbohydrate Polymers | Year: 2011

Food-grade galacto-oligosaccharides (GOS) are commercially available as transparent syrups or dried powders. Food powders can be found in an amorphous metastable state which is very sensitive to changes in temperature and moisture content. In this work the impact of water content on thermal behavior and relative humidity on water sorption behavior of amorphous GOS powders were studied. Results from differential scanning calorimetry (DSC) and sorption isotherms suggest that GOS mixture studied, with high content of oligosaccharides, has low ability to crystallize. A dramatic decrease in the stability of GOS powders occurred above critical water content (12-14 g/100 g) and corresponding critical water activity (0.55-0.62). Above these conditions GOS powder lost its amorphous character, collapsed and shrank, as the powder became a transparent "solution-like" material. The knowledge about the physicochemical changes, acquired during the present study, should be used to a proper control of processing and storage conditions to achieve and maintain optimum powder quality with desired properties. © 2010 Elsevier Ltd. All rights reserved. Source


Teixeira V.,CIQ UP | Feio M.J.,REQUIMTE | Bastos M.,CIQ UP
Progress in Lipid Research | Year: 2012

Antimicrobial peptides (AMPs) take part in the immune system by mounting a first line of defense against pathogens. Recurrent structural and functional aspects are observed among peptides from different sources, particularly the net cationicity and amphipathicity. However, the membrane seems to be the key determinant of their action, either as the main target of the peptide action or by forming a barrier that must be crossed by peptides to target core metabolic pathways. More importantly, the specificity exhibited by antimicrobial peptides relies on the different lipid composition between pathogen and host cells, likely contributing to their spectrum of activity. Several mechanisms of action have been reported, which may involve membrane permeabilization through the formation of pores, membrane thinning or micellization in a detergent-like way. AMPs may also target intracellular components, such as DNA, enzymes and even organelles. More recently, these peptides have been shown to produce membrane perturbation by formation of specific lipid-peptide domains, lateral phase segregation of zwitterionic from anionic phospholipids and even the formation of non-lamellar lipid phases. To countermeasure their activity, some pathogens were successful in developing effective mechanisms of resistance to decrease their susceptibility to AMPs. The functional and integral knowledge of such interactions and the clarification of the complex interplay between molecular determinants of peptides, the pathogen versus host cells dichotomy and the specific microenvironment in which all these elements convene will contribute to an understanding of some elusive aspects of their action and to rationally design novel therapeutic agents to overcome the current antibiotic resistance issue. © 2012 Elsevier Ltd. All rights reserved. Source


Adao R.,CIQ UP | Bai G.,CIQ UP | Loh W.,University of Campinas | Bastos M.,CIQ UP
Journal of Chemical Thermodynamics | Year: 2012

The use of a good chemical calibration or test reaction in Isothermal Titration Calorimetry is crucial for getting reliable enthalpy values that can be compared across different laboratories. Indeed most titration calorimeters are used to measure both equilibrium constants and molar enthalpies of reaction. But a necessary prerequisite for such measurements is to first perform the enthalpy measurement accurately and precisely. The values of the equilibrium constant(s) are then calculated by regression from an appropriate model. As such, we found it timely to extensively test a previously proposed test reaction, the dilution of propan-1-ol into water, using two calorimeters of different design (heat conduction and power compensation calorimeters) and sensitivity. Experiments were performed at 298.15 K for the previously suggested 10% mass fraction propan-1-ol solution, as well as for the lower concentrations of 5% and 2% mass fractions. Due to our capacity to use insertion heaters with one of the used calorimeters, which allows for very accurate calibration constants to be obtained, we also determined a value for the enthalpy of dilution of 10% mass fraction solution at 308.15 K, previously not available, and closer to the temperatures commonly used in titration experiments involving biological samples. The observed change in the enthalpy of dilution was found to decrease in absolute value, but to an extent that did not justify the determination of new values for the less concentrated solutions. The values obtained with the two calorimeters are in excellent agreement, as well as with the values from the literature for the 10% mass fraction solution at 298.15 K. This reaction is thus again proposed as an excellent test reaction and the detailed conditions of their use depending on instrument sensitivity are suggested. In summary, the values for the enthalpies of dilution to infinite dilution ΔdilHm at 298.15 K are -(1.540 ± 0.021) kJ·mol -1, -(0.604 ± 0.020) kJ·mol -1, and -(0.186 ± 0.011) kJ·mol -1 for the 10%, 5%, and 2% mass fraction solutions, respectively, and at 308.15 K -(1.486 ± 0.017) kJ·mol -1 for the 10% mass fraction solution. © 2012 Elsevier Ltd. All rights reserved. Source

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