Introduction
Historical Outline
Chemical Structure
Conformation
Occurrence and Source Dependence
Physiological Function
Chemical Analysis and Detection
Chemical Composition and Sequence
Molecular Mass
Detection and Quantification
Biosynthesis and Biodegradation
Production: Biotechnological and Traditional
Isolation from Natural Sources / Fermentative Production
Molecular Genetics and
in vitro
Modification
Current and Expected World Market and Costs
Alginate Manufacturers
Properties
Physical Properties
Material Properties
“Biological” Properties
Applications
Technical Utilization
Medicine and Pharmacy
Foods
Relevant Patents
Outlook and Perspectives
Acknowledgements
Ca-alginate gels were studied by small-angle X-ray scattering and rheology to determine relations between chemical composition and concentrations of the alginate and the elasticity and structure of the gels. The gels were prepared by in situ release of Ca 2+ from either Ca-EGTA or CaCO3 with total Ca 2+ concentration in the range 5-30 mM. Alginates with low (39%), intermediate (50%), and high (68%) fractions of R-L-GulA originating from the brown algae Ascophyllum nodosum, Laminaria hyperborea leaf, and Laminaria hyperborea stipe, respectively, were employed. Two to three different degrees of polymerization for each chemical composition were used in the experiments. The excess small-angle X-ray scattering for the alginates in solution yielded linear cross-sectional Guinier plots, and the cross-sectional radius of gyration, R g,c, was determined to be 3.1-4.6 Å. The SAXS profiles of the alginate gels depended on the alginate concentration, Ca 2+ concentration, and the alginate composition. The SAXS data suggested that dimerization of chain segments was the principal association mode at low fractional Ca 2+ saturation of guluronic acid of the alginate. Increasing the fractional Ca 2+ saturation of guluronic acid, either by the concentrations or selection of alginate source, yielded coexisting lateral association modes, as manifested in a curvature in the cross-sectional plots. The coexisting junction zone multiplicities occur because of a delicate balance between the block length distribution of the R-L-GulA residues, polymer concentration, and Ca 2+ . These results are quantitative extensions of the "egg-box" model used to describe ionotropic gelation of alginate and hence enhance the understanding of the structure-function relationship of alginate gels.
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