Elucidation of the emulsification properties of sugar beet pectin.

A protocol has been developed to fractionate sugar beet pectin using hydrophobic affinity chromatography. Three samples eluted from the column using 4 M NaCl as solvent (fractions 1A, 1B, and 1C), two fractions eluted using 2 M NaCl (fractions 2A and 2B), and one fraction eluted using water (fraction 3). The fractions were shown to be very polydisperse, and differences between the GPC refractive index and UV absorbance (214 nm) elution profiles demonstrated chemical heterogeneity. They were found to contain significantly different proportions of protein (1A, 2.79%; 1B, 0.97%; 1C, 0.77%; 2A, 1.41%; 2B, 5.09%; and 3, 5.89%) and ferulic acid (approximately 1A, 0.5%; 1B, 0.5%; 1C, 0.9%; 2B, 1.5%; and 3, 2%). The weight-average molecular mass, M(w), of the fractions also varied (1A, 153 kDa; 1B, 155 kDa; 1C, 306 kDa; 2A, 562 kDa; 2B, 470 kDa; 3, 282 kDa). Three fractions, that is, 1A, 1B, and 3, produced orange oil emulsions with a relatively small droplet size that were stable over a period of weeks. The other three fractions (1C, 2A, and 2B with higher M(w) values) produced emulsions with an initially larger droplet size, and the droplet size increased considerably over time. The increased droplet size may be influenced by the viscosity of the aqueous continuous phase. There was no simple relationship between protein or ferulic acid content and emulsification ability. For example, fraction 1B, which contained the lowest proportion of both protein and ferulic acid, produced stable emulsions of similar droplet size to fraction 3, which contained the largest proportion of protein and ferulic acid. The role of protein in the emulsification process was investigated by measuring the amount of protein in the aqueous phase before and after emulsification. It was clearly demonstrated that proteinaceous material adsorbed at the oil-water interface. It is evident that the emulsification properties of sugar beet pectin are influenced by the accessibility of the protein and ferulic acid groups to the surface of the oil droplets, the proportion of ester groups, and the molecular mass distribution of the fractions.

Solution rheology of kappa-carrageenan in the ordered and disordered conformations.

The order-disorder conformational transition of kappa-carrageenan, induced by both electrolyte and temperature, was found to give rise to significantly different rheological properties under shear flow, extensional flow, and small deformation oscillation regimes. Shear flow displayed only shear thinning or Newtonian behavior, depending of the chain conformation. A larger range of properties was observed in elongational flow. Strain-thinning behavior was observed in the ordered conformation while strain thickening occurred in the disordered conformation. These results are discussed as a function of the chain conformation.

A rheological study of the order-disorder conformational transition of xanthan gum.

The rheological properties of a moderately concentrated solution of xanthan gum in both the ordered and the disordered state have been studied. Oscillatory shear, steady shear flow, and extensional flow experiments have been performed at different temperatures, covering the order-disorder transition determined by differential scanning calorimetry (DSC). The principle of time/temperature superposition was applied to the xanthan solutions for the different types of flow. Although a master curve covering six decades of frequency could be obtained for the storage modulus over the entire investigated temperature range, less agreement was found for the other modulus. This indicates that the order-disorder transition reflects changes on the molecular scale and slight modification of the physical network structure. To the authors' knowledge, this is the first time that this transition has been observed using these different rheological techniques.

The influence of temperature on the characterization of water-soluble polymers using asymmetric flow field-flow-fractionation coupled to multiangle laser light scattering

Asymmetrical flow field-flow fractionation coupled to multiangle laser light scattering has been shown to be an effective method to determine the molar mass distribution of polysaccharides. Two polymer standards, dextran and pullulan, were analyzed in the temperature range 30-60 degrees at intervals of 10 degrees C. The weight average molar mass and molar mass distribution obtained at each temperature agreed well with quoted values. The diffusion coefficient, hydrodynamic radius, radius of gyration, and activation energy of diffusion were calculated and all agreed well with literature data obtained by dynamic and static light scattering. The asymmetry factor Rg/Rh suggests a flexible random coil conformation for both polymers, which was supported by the molar mass dependence of both the radius of gyration and the hydrodynamic radius. The results show the potential of asymmetric flow field fractionation coupled to multiangle laser light scattering in undertaking measurements of molar mass distribution as a function of temperature.

Organisation and association of kappa-carrageenan helices under different salt conditions.

Mixtures of the added salts NaI and CsI can be used to gradually 'tune' the propensity of kappa-carrageenan (KC) helices to aggregate in solution. We show that this method can be used to resolve the molecular events by which helix formation, under certain conditions, leads to gelation. We also present an overview of the various states of aggregation and organisation that appear for helical KC (non-degraded or ultrasonically degraded) when the NaI/CsI ratio and the concentration of KC are varied. A transition to rigid, superhelical rods is found above a well-defined fraction of cesium. This transition is reflected in a range of experimental measurements, such as cryo-transmission electron microscopy, optical rotation, viscometry and small deformation oscillatory measurements. The superhelical-rod state also seems essential for the association of KC with locust bean gum, and locust bean gum is found to stabilise this state. Novel states of KC alone have been found at cesium contents below the transition threshold. Non-degraded KC forms weak gels at sufficiently high concentrations (> ca. 1%). In contrast, ultrasonically degraded KC forms a chiral nematic liquid crystalline phase at sufficiently high concentrations (> ca. 5%) under these salt conditions.

On the structure of aggregated kappa-carrageenan helices. A study by cryo-TEM, optical rotation and viscometry.

Cryo-transmission electron microscopy (cryo-TEM), viscometry and optical rotation have been used to study the microstructure of dilute solutions of helical kappa-carrageenan under varied electrolyte composition (0.1 M of NaI, CsI and mixtures of the two salts). Microfibers (300-400 nm in length) were observed above a critical cesium content, while below that no microstructure was seen in the micrographs. A drastic increase in the specific viscosity and an onset of thermal hysteresis in the optical rotation above the same critical cesium content provide clear evidence of aggregate formation. This leads to the conclusion that the observed microfibers are aggregates consisting of several helices. At high proportions of cesium, further aggregation of the microfibers was observed by cryo-TEM.