Structural Principles of Polysaccharide Gels.

Abstract

The author and colleagues have proposed a gelation mechanism for K-carrageenan , c-car-rageenan, agarose (agar), gellan gum, curdlan, amylose, and alginic acid at the molecular level in aqueous solutions in preceding papers. The synergistic gelation mechanism between xanthan gum and galactomannans (locust-bean, tara-bean and guar gum), and konjac glucomannan , where trisac-charide side-chains of the former molecule take part in the interaction , have been proposed. The synergistic gelation mechanism between K-carrageenan and galactomannan (locust-bean gum) has also been proposed. Recently, we have proposed gelatinization and retrogradation mechanisms of rice starch. The polysaccharides in water changed into an ice-like structure with hydrogen bonding between polymer and water molecules, and between water molecules even at a concentration range of 0.1-1.0% (w/v) at room temperature, resulting in gelation. Such dramatic changes from liquid into gels have not yet generally been understood at the molecular level. The research conducted by the author now makes it possible to discuss, in principle, because structure-function relationships from the viewpoint of rheology not only of the gelling polysaccharides mentioned above , but also of non-gelling welan, rhamsan, S-657 gum, schizophyllan , and amylopectins (rice and potato), the structure of which is similar to that of gelling gellan gum, curdlan and amylose , have also been analyzed at the molecular level in our preceding papers. In the course of the rheological studies of poly-saccharides, we have discussed the molecular origin for their rheological characteristics and proposed a gelation mechanism for k-carrageenan,1,2) c-carrageenan,3) agarose (agar),4) gellan gum,5-9) curdlan,10,11) amylose,12-14) and alginic acid15) at the molecular level in aqueous solutions. We also proposed synergistic gelation mechanism for a mixture solutions of xanthan gum and galactomannans (locust-bean, tara-bean, and guar gum),16-20) and konjac glucomannan,21-23) where trisaccharide side-chains of the former molecules take part in the interaction ; the model of which might provide the existence for D-mannose-specific binding sites in the host-pathogen relationships and in the cell recognition processes.18,20,21) Furthermore, the synergis-tic association site between K-carrageenan and ga-lactomannan (locust-bean gum) has also been proposed at the molecular leve1.24) This model may also provide the existence for D-mannose-specific binding sites between cell-surface proteins and mannose-rich oligo-and polysaccharides.