Browsing by Author "Fernandes, Paulo B."
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- Determination of the physical functionality of galactomannans in kappa-carrageenan/galactomannan mixed systems by periodate oxidationPublication . Fernandes, Paulo B.Galactomannan samples of different origins (guar gum, tara gum, and locust-bean gums), with mannose-to-galactose (M/G) ratios from 1·7 to 4·8, have been characterized. They exhibited strong differences with respect to their molecular weight and their fine structure (M/G). The different locust-bean-gum samples differed significantly in this respect from each other. All galactomannans were submitted to periodate oxidation. The periodate oxidation of galactomannan samples was characterized by the formic acid liberated. As expected, the formic acid liberated was directly related to the (M/G)ratios of galactomannan samples. Thus galactomannan periodate oxidation was shown to be a simple and precise analytical method to predict the (M/G)ratio of galactomannan samples. It was demonstrated that galactomannan periodate oxidation, as a measure of the Image ratio, can be directly related to the physical functionality of galactomannans in terms of synergistic interactions between the kappa-carrageenan and the galactomannans.
- Influence of galactomannan on the structure and thermal behaviour of xanthan/galactomannan mixturesPublication . Fernandes, Paulo B.Mixed gels of xanthan gum and galactomannans (guar, whole and fractionated locust bean gum — LBG) were compared by means of oscillatory shear measurements. Whatever the LBG fraction, a synergistic maximum was observed when the ratio of xanthan to galactomannan was 1:1. However, the magnitude of this maximum varied with the LBG fraction used. The thermal behaviour of 1:1 xanthan/LBF fractions was characterized by cooling-heating cycles. A slight thermal hysteresis was systematically described for the several xanthan/LBG fraction systems. It was observed that the mannose to galactose (M/G) ratio of LBG fractions determined the sol-gel transition (gelation and melting temperature) of the xanthan/galactomannan mixed systems. From the galactomannan fine structure and thermorheological profiles it is evident that the higher the M/G ratio of galactomannan samples, the higher is the synergistic interaction as is also the transition temperature of the xanthan/LBG systems.
- Microbiological and rheological studies on Portuguese kefir grainsPublication . Pintado, Manuela E.; Silva, J. A. Lopes da; Fernandes, Paulo B.; Malcata, F. Xavier; Hogg, TimThe native bacteria and yeasts present in Portuguese kefir grains stored under four distinct sets of environmental conditions have been isolated and identified on the basis of morphology and biochemical tests. The microbial population of the kefir grains as a whole has been characterized in terms of rates of biomass production and formation of lactic acid and ethanol. The rheological properties of the purified polysaccharide (kefiran) produced by the microflora of the grains and accumulated therein were studied in a low water activity solvent and as a component of a binary gel containing either k-carrageenan or xanthan gum.
- Rheological description at the minimum gelling conditions of kappa-carrageenan/locust bean gum systemsPublication . Fernandes, Paulo B.; Gonçalves, M.P.; Doublie, Jean-LouisKappa-carrageenan/locust bean gum interactions at the minimum gelling concentration have been studied by dynamic and viscosity measurements at 15°C. Both rheological methods used have been shown to be complementary. The existence of a weak network structure exhibiting thixotropic behaviour has been observed. The formation of the weak network is discussed.
- Viscoelastic characteristics of whey protein systems at neutral pHPublication . Fernandes, Paulo B.The gelation properties of whey proteins alone and in presence of NaCl, KCl, CaCl2 and L-lysine upon heating to 80°C were characterised at pH 7 by oscillatory shear measurements. At the sol—gel transition, the whey protein system gave G′(ω) and G″(ω) curves with a slope of 0.5–0.6. For higher concentrations the gel behaviour was typical for an homogeneous network and whey protein gels present a gel structure with a fractal dimension of 2.7. NaCl, KCl, CaCl2 and L-lysine increased the elasticity of whey protein gels in a similar way. At ionic strength 0.03 the Na-, K- and L-lysine-WP gels obtained were transparent, while the Ca-WP gels presented an opaque particulate structure.