Electrostatics, polysaccharides

It is well known the tendency of polysaccharides to associate in aqueous solution. These molecular associations can deeply affect their function in a particular application due to their influence on molecular weight, shape and size, which determines how molecules interact with other molecules and water. There are several factors such as hydrogen bonding, hydrophobic association, an association mediated by ions, electrostatic interactions, which depend on the concentration and the presence of protein components that affect the ability to form supramolecular complexes. 

Then, the macromolecular characterization is necessary to obtain the molecular weight distribution of the polymeric material and the average molecular weights. For this purpose, the first important condition is to get a perfectly molecular soluble material which means to avoid aggregation and/or take off insoluble material. This point was previously discussed [12]. The polysaccharide must be isolated preferentially as a sodium salt form to be fully soluble in water or in presence of some NaCI used to screen electrostatic interactions. 

Polymeric gels (mainly polyacrylamide and polysaccharides) have been also used as substrates for the attachment of NAs. These materials represent three-dimensional hydrophiUc matrices through which the biomolecules can diffuse and interact. Polymeric gels cannot be used as substrates for DNA array production without their previous immobibzation to a solid support (usually a glass sbde) in the form of pads. This fixation can be stabibzed covalently or electrostatically, depending on the type of gel and the support involved. 

SUVs have also been stabilized by coating their outer surfaces with chitin [328], polylysine [329-332], polyelectrolytes [333], and polysaccharides [334]. Advantage has also been taken of electrostatic interactions to attract oppositely charged polyelectrolytes to outer SUV surfaces and subsequently polymerize them in situ [335-339]. These systems have been referred to as liposomes in a net [72]. A particularly telling example is the attachment of a two-dimensional polymeric network either to the inner or to the outer surfaces of SUVs by ion exchanging the vesicle counterions with oppositely charged polymerizable short-chain counterions and their subsequent polymerization (Fig. 42) [340-342]. 

The electrostatic interaction between oppositely charged protein and polysaccharide can be utilized for encapsulation and delivery of hydro-phobic nutraceuticals. As a result of this interaction, we may have either complex coacervation (and precipitation) or soluble complex formation, depending on various factors, such as the type of polysaccharide used (anionic/cationic), the solution pH, the ionic strength, and the ratio of polysaccharide to protein (see sections 2.1, 2.2 and 2.5 in chapter seven for more details) (Schmitt et al, 1998 de Kruif et al., 2004 Livney, 2008 McClements et al, 2008, 2009). The phenomenon of complex... 

Electrostatic and non-electrostatic biopolymer complexes can also be used as effective steric stabilizers of double (multiple) emulsions. In this type of emulsion, the droplets of one liquid are dispersed within larger droplets of a second immiscible liquid (the dispersion medium for the smaller droplets of the first liquid). In practice, it is found that the so-called direct water-in-oil-in-water (W/O/W) double emulsions are more common than inverse oil-in-water-in-oil (O/W/O) emulsions (Grigoriev and Miller, 2009). In a specific example, some W/O/W double emulsions with polyglycerol polyricinoleate (PGPR) as the primary emulsifier and WPI-polysaccharide complexes as the secondary emulsifying agent were found to be efficient storage carriers for sustained release of entrapped vitamin Bi (Benichou et al., 2002). 

Dickinson, E. (1998). Stability and rheological implications of electrostatic milk protein-polysaccharide interactions. Trends in Food Science and Technology, 9, 347-354. 

An increasing concentration of anionic surfactant can strengthen the electrostatic repulsive forces between the maltodextrin associates, as modified by the addition of the negatively charged head-groups of the surfactant to the neutral molecules of polysaccharide. The consequence of this effect is a reduction in the extent of maltodextrin association. In combination with the other effects, this leads to parameter dependency with a local maximum and minimum below the cmc of the surfactant (see Figures 6.10a and 6.10b). 

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