Anionic polysaccharides, interaction

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

Marine sulfated polysaccharides (MSPs), such as sulfated fucans (SFs), sulfated galactans (SGs), and glycosaminoglycans (GAGs) isolated from invertebrate animals, are highly anionic polysaccharides capable of interacting with certain cationic proteins, such as... 

It seems that there is probably greater availability of positively charged residues on the adsorbed protein for electrostatic interaction with sulfate groups of the anionic polysaccharide. This could lead to a greater extent of neutralization of dextran sulfate as a result of complex formation, and consequently to a lower thermodynamic affinity of the complexes for the aqueous medium and a lower value of the ( -potential for emulsion droplets in bilayer emulsions. 

Imeson, A.P., Led ward, D.A., Mitchell, J.R. (1977). On the nature of the interaction between some anionic polysaccharides and proteins. Journal of Agricultural and Food Chemistry, 28, 661-667. 

Figure 10. Drawing of hydrogen bonding interactions between polysaccharide and copolymer molecules, and electrostatic interactions between the poly anion and protons. ( 2 ) poly anion (--) polysaccharide...

In the pH range close to the protein s lEP an interesting phenomenon of non-uniform redistribution of protein molecules among polysaccharide chains occurs (Tolstoguzov et al. 1985). The reason is that in the vicinity of the protein lEP the hydrophobic protein-protein and electrostatic protein-polysaccharide interactions can be energetically comparable with each other. Protein-protein association on the anionic polysaccharide matrix (or self-association of proteins), which is mainly due to hydrophobic interactions, is usually enhanced when the pH approaches the protein lEP. Accordingly, under conditions of a relatively weak protein-polysaccharide interaction, each free site situated near the site on the polysaccharide chain already occupied by a protein molecule becomes thermodynamically preferable for further binding of protein molecules. This leads to cooperative protein adsorption on an anionic polysaccharide. Some parts of polysaccharide chains tend to be completely covered by protein molecules (as in a virus) while other parts are completely free of protein. 

The formation of complexes affects both particle-solvent and particle-particle interactions. The solubility of proteins may be increased by their electrostatic complexing with anionic polysaccharides. Formation of titration-complexes may increase protein solubility and inhibit protein precipitation at the lEP. Anionic polysaccharides can act as protective hydrocoUoids inhibiting aggregation and precipitation of like-charged dispersed protein particles, for example, of denatured proteins. This protective action also can increase the stability of protein suspensions and oil-in-water emulsions stabilized by soluble protein-anionic polysaccharide complexes. 

At the second critical pH (pH,, ), which is usually below the protein isoelectric point, strong electrostatic interaction between positively charged protein molecules and anionic polysaccharide chains will cause soluble protein/polysaccharide complexes to aggregate into insoluble protein/polysaccharide complexes. For negatively charged weak acid-based (e.g., carboxylic acid) polysaccharides like pectin, with the decrease of pH below the pKa of the polysaccharide, protein (e.g., bovine serum albumin (BSA))/polysaccharide (e.g., pectin) insoluble complexes may dissociate into soluble complexes, or even non-interacted protein molecules and polysaccharide chains, due to the low charges of polysaccharide chains as well as the repulsion between the positively charged proteins (Dickinson 1998). 

The more polymer chains interact with the solvent, the less they will interact with each other and, for neutral polysaccharides in water or anionic polysaccharides in salt solutions, lies between 0.3 and 05. ... 

Interaction Between Metal Cations and Anionic Polysaccharides... 

In complex coacervation (20 pm to 1 nun), for example, aqueous solutions of active component (AC), polyanion (-) and polycation (+) are mixed. The two polymers with opposite charges (electrostatic interactions) will interact to form a deposit of coacervate at the surface of AC (i.e., acacia gum, alginate CMC with gelatine proteins and anionic polysaccharides) (De Kruif et al., 2004). Reticulation may be provoked by dilution, and modification of pH, tanperature (Figure 39.10). Gelatine and acacia gum (opposite charge at low pH) were used to encapsulate flavor lipophilic oil to be used in frozen foods and released upon heating (Yeo et aL, 2005), with liquid or solid core (Leclercq et al., 2009). 

Figure 20.22. Phase separation in mixtures of a polyelectrolyte and an oppositely charged surfactant changes from associative (a,b), to no phase separation (c) and finally to segregative (d,e) as electrolyte is added. This example shows mixtures of a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB), and an anionic polysaccharide, sodium hyaluronate (NaHy). (Redrawn from B. Lindman and K. Thalberg, in Interactions of Surfactants with Polymers and Proteins E. D. Goddard and K. P. Ananthapadmanabhan (Eds), CRC Press, Boca Raton, FL, 1993, p. 254)...

Chitosan is a polyamine with a high degree of positive charge at pH below pK, of the amine groups (p/fj 5.5-6.5). Therefore, chitosan is prone to interact readily with negatively charged substances such as proteins, anionic polysaccharides, or fatty acids. 

The anionic polysaccharides, though structurally diverse, share some common characteristics. Most of those described above interact strongly with multivalent cations calcium ion (Ca ), in particular, binds tightly. This binding can be beneficial, e.g., the gel formation of... 

The addition of cationic surfactant to an anionic polysaccharide solution shows its greatest effect near the surfactant cmc. As the surfactant concentration increases beyond the cmc, the polysaccharide may go back into solution or it may form an insoluble complex, flocculate, and settle out of solution. In general, as the polysaccharide s anionic charge increases, so does its interaction with cationic surfactants. As an example, alginic acid binds more strongly to cationic surfactants than carboxymethylcellulose. 

The behavior of anionic polysaccharides with nonionic and amphoteric surfactants (betaines) is more complex. For example, nonionic surfactants can form charge transfer complexes with highly charged polysaccharides. Amphoteric surfactants can have various charges and various degrees of interaction with anionic polysaccharides depending on the... 

It was seen that anionic surfactants interact with the positive charge of cationic polysaccharides even at concentrations well below the surfactant s cmc. There is a rapid increase in the viscosity of 1.0 wt% polyquaternium-10 solutions as the anionic surfactant begins to neutralize the charge on the cationic polymer (Fig. 26). As shown earlier (Fig. 22), this solution viscosity response is characteristic of the cationic HEC/anionic surfactant combination and does not appear to occur in the juxtaposed anionic cellulose/cationic surfactant combination. 

A unique and useful complex of PQ-24 and hyaluronic acid (Sections in.A.l.e and III.F.1) has been described (74,192). The strong ionic interaction of anionic hyaluronic acid and cationic PQ-24 is tempered by the hydrophobic groups allowing stable solutions containing both components. The PQ-24 aids in delivering the hyaluronic acid, anchors the expensive anionic polysaccharide to the skin, and takes greater advantage of its beneficial effects before the polysaccharide is washed off the skin. 

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