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M P Gonçalves

Publications and source records attributed to M P Gonçalves.

8 recordsLinked to original sources
PubMed2006

Thermal and viscoelastic properties of kappa/iota-hybrid carrageenan gels obtained from the Portuguese seaweed Mastocarpus stellatus.

The potential use of the underexploited Portuguese seaweed Mastocarpus stellatus as a source of natural thickening and gelling agents for food applications has been investigated. The alkaline pretreatment duration and extraction parameters (pH, temperature, and extraction duration) of seaweeds have been systematically varied in order to produce kappa/iota-hybrid carrageenans exhibiting a wide range of chemical properties. The mechanical spectra and the setting and melting temperatures of gels obtained by cooling 1.5 wt % extracted biopolymers solutions in 0.05 mol/dm3 KCl were measured by means of small amplitude oscillatory shear experiments. Gels showing elastic storage moduli ranging from 250 to 2750 Pa with no water syneresis could be obtained, and the relationships between the thermal properties and elasticity of the gels were evidenced. Gels mechanical properties are shown to correlate well with polysaccharides chemical parameters such as the degree of sulfate groups, the molecular weight distribution, and the relative content in iota-carrageenan monomers as determined by FTIR spectroscopy.

Carrageenan↗
PubMed2006

Effect of extraction parameters on the chemical structure and gel properties of kappa/iota-hybrid carrageenans obtained from Mastocarpus stellatus.

Extraction parameters (temperature, pH, duration) and alkaline pre-treatment duration have been systematically varied in the aim of exploring their impact on both chemical structure and gelling properties of carrageenan biopolymers obtained from Mastocarpus stellatus seaweeds, collected on the Northern coast of Portugal. Increasing the alkaline pre-treatment duration PT leads to kappa/iota-hybrid carrageenans containing less sulphate groups and biological precursor monomers. As a result, gel properties in the presence of KCl are improved as demonstrated by the increase in the Young's modulus with parameter PT. Increasing the extraction duration t ameliorates the biopolymer yield with no significant change in the complex kappa/iota-hybrid carrageenan chemical structure. However, smaller molecular weights are obtained and gel properties are seen to be negatively affected. Extraction temperature and pH have dramatic effects on the biopolymer gel strength, and a set of extraction parameters optimized with respect to extraction yield and gel properties is reported. In addition, kappa/iota-hybrid carrageenans obtained throughout this study exhibit a wide range of gel strengths in KCl, and allow us to present correlations between gel thermal properties and the kappa/iota-hybrid carrageenans chemical structure.

Carbohydrate Conformation↗
PubMed2000

Rheological properties of mixtures of kappa-carrageenan from Hypnea musciformis and galactomannan from Cassia javanica.

Mixed gels of kappa-carrageenan (kappa-car) from Hypnea musciformis and galactomannans (Gal) from Cassia javanica (CJ) and locust bean gum (LBG) were compared using dynamic viscoelastic measurements and compression tests. Mixed gels at 5 g/l of total polymer concentration in 0.1 M KCl showed a synergistic maximum in viscoelastic measurements for kappa-car/CJ and kappa-car/LBG at 2:1 and 4:1 ratios, respectively. The synergistic maximum obtained from compression tests carried out for mixed gels at 10 g/l of total polymer concentration in 0.25 M KCl was the same for both kappa-car/CJ and kappa-car/LBG gels. An enhancement in the storage modulus (G') and the loss modulus (G") was observed in the mechanical spectra for the mixtures in relation to kappa-car. The proportionally higher increase in G" compared with G', as indicated by the values of the loss tangent (tandelta), suggests that the Gal adhere non-specifically to the kappa-car network.

Carrageenan↗
PubMed2000

Phase equilibria and mechanical properties of gel-like water-gelatin-locust bean gum systems.

The establishment of phase equilibrium in aqueous gelatin-locust bean gum (LBG) systems in the process of cooling from 313 to 291 K in specific conditions, passes ahead of the gelation process(.) This allows the suggestion that macrostructure and mechanical properties of the system can be predicted on the basis of knowledge of its phase diagram, obtained for the liquid gelatin-LBG systems comprising gelatin molecular aggregates. Textural and rheological analysis of gel-like gelatin-LBG systems demonstrate the effect of two factors determining their mechanical properties and acting opposite each other when the concentration of LBG in the system increases: concentration of gelatin by LBG in the process of phase separation, and decrease in the density of the gel network.

Galactans↗
PubMed1999

The effect of phase viscosity ratio on the rheology of liquid two phase gelatin-locust bean gum systems.

The rheological behaviour of liquid two phase gelatin-locust bean gum (LBG) systems, comprising of (a) liquid LBG enriched continuous phase, and (b) flow-deformable gelatin-enriched dispersed particles seems to be determined, at the same phase composition, by phase viscosity ratio (mu). In the mu range from 0.03 to 0.21, viscosity dropped to values noticeably lower (13-40 times) than those of the corresponding LBG solution. Decrease in the viscosity of the mixtures was not observed at mu = 0.5-0.6, corresponding that to the maximum energy scatter inside the droplets, in agreement with Mason's conception of droplet deformation and disruption of liquid Newtonian emulsions.

Galactans↗
PubMed1999

Solution properties of the galactomannans extracted from the seeds of Caesalpinia pulcherrima and Cassia javanica: comparison with locust bean gum.

The galactomannans from the seeds of Caesalpinia pulcherrima and Cassia javanica were extracted from the milled seeds in water at room temperature. Both products, as well as a commercial sample of locust bean gum (LBG), were purified by precipitation in isopropyl alcohol. The intrinsic viscosity determined for LBG, [eta] = 15.2 dl/g, was slightly higher than those for the other two galactomannans. The dependence of the specific viscosity at zero shear rate on the coil overlap parameter, C[eta], revealed a similar behaviour for the three galactomannans. A master curve was obtained with a critical concentration, C*, at C*[eta] = 3.3. The slope of the curve in the concentrated regime is higher than the values in the range of 3.9-6.6, obtained for the generalized behaviour of several random coil polysaccharides. Dynamic experiments showed that, at the concentrations studied, the behaviour of the galactomannans was typical of systems with predominant entanglement networks in the region between the terminal and plateau zones of frequency response. The correlation between dynamic and steady shear properties (Cox Merz rule) was satisfactory for the three galactomannans.

Fabaceae↗
PubMed1995

Kinetics and thermal behaviour of the structure formation process in HMP/sucrose gelation.

The concentration and temperature dependence of the gelation kinetics of high-methoxyl pectin (HMP; 60% sucrose, pH 3) was investigated using measurements of small-amplitude oscillatory shear. The rate of gelation close to the gel point can be described as a second-order rate process using the kinetic model of Ross-Murphy (Carbohydr. Polym. 1991, 14, 281) and a critical exponent close to that predicted by the percolation approach. The modulus after a long ageing time showed a power concentration dependence with an exponent around 3.1, higher than the classical square of concentration dependence, which was probably either due to the nonequilibrium state of the HMP gels even after long ageing times, or due to the proximity of the concentration range studied to the critical gelling concentration. The gelation rate of HMP/sucrose systems is strongly dependent on the temperature. An Arrhenius relationship was applied to describe this dependence. Two different processes are proposed to explain the discontinuity observed, each one having rates with different temperature dependence. The applicable kinetics at longer times are quite different, with a lower dependence on polymer concentration and ageing temperature. A non-isothermal kinetic model was used to describe the gelation process of the HMP/sucrose system during cooling.

Food Technology↗