Dispersions polysaccharide-water interactions

The effect of heat on the polysaccharide-water interaction in several dispersions and suspensions was studied by comparative viscometry and rheometry (Tables I-IV). The polysaccharides were the purest manufacturers grade laboratory washed and dried before dispersion. The dispersion concentrations were below c to accommodate capillary viscometry, and the suspension concentrations were above c to accommodate rheometry. It is seen in Tables I and II that the cellulose derivatives made the most stable dispersions and the propylene glycol alginate made the least. Dispersions of the neutral polysaccharides were more stable than those of the ionic polysaccharides. From Tables III and IV, it can be argued that suspensions benefit... 

The solute-water interaction extends 1-3 nm (Israelachvili, 1992) and decays exponentially with distance (Van de Ven, 1989). Non-free-draining water is water within this distance traveling with the same velocity as the particle nucleus. At the interface between the non-free-draining (bound) water and the outer volume of free-draining water traveling at a different velocity, an fc [Eq. (3.27)] is generated. In this sense, hydration and the imaginary shear plane have enormous ramifications for human oral sensations elicited by dispersed polysaccharides. 

Water molecules of hydrophilic sols, in the vicinity of dispersed molecules of high molecular weight substances (proteins and polysaccharides), are relatively tightly associated by non-bonding interactions. They are usually in the state of thermodynamic equi-Hbrium and are therefore relatively stable. Their viscosity and surface tension are significantly different (higher) than the viscosity and surface tension of the pure dispersion medium (water). 

Starches. Starch (qv) granules must be cooked before they wiU release their water-soluble molecules. It is common to speak of solutions of polysaccharides, but in general, they do not form tme solutions because of their molecular sizes and intermolecular interactions rather they form molecular dispersions. The general rheological properties of polysaccharides like the starch polysaccharides are described below under the discussion of polysaccharides as water-soluble gums. Starch use permeates the entire economy because it (com starch in particular) is abundantly available and inexpensive. Another key factor to its widespread use is the fact that it occurs in the form of granules. 

For simple fluids, also known as Newtonian fluids, it is easy to predict the ease with which they will be poured, pumped, or mixed in either an industrial or end-use situation. This is because the shear viscosity or resistance to flow is a constant at any given temperature and pressure. The fluids that fall into this category are few and far between, because they are of necessity simple in structure. Examples are water, oils, and sugar solutions (e.g., honey unit hi.3), which have no dispersed phases and no molecular interactions. All other fluids are by definition non-Newtonian, so the viscosity is a variable, not a constant. Non-Newtonian fluids are of great interest as they encompass almost all fluids of industrial value. In the food industry, even natural products such as milk or polysaccharide solutions are non-Newtonian. 

The solvent quality of water deteriorates by additions of alcohol and salt, singly and combined. Polyanions are especially sensitive to cations and are invariably precipitated by the di- and polyvalent species in sufficiently high concentration. Charge suppression by nonsolvents and cations decreases the polyanionic coil volume (vc) and simultaneously reverses the solute-solvent interaction through 0 to precipitation. Micromolecules can alter the dispersion rheology (Pastor et al., 1994) of charged an neutral polysaccharides. 

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. 

In parallel, another important (although less direct) technique for measuring forces between macromolecules or lipid bilayers was developed, namely, the osmotic stress method [39-41]. A dispersion of vesicles or macromolecules is equilibrated with a reservoir solution containing water and other small solutes, which can freely exchange with the dispersion phase. The reservoir also contains a polymer that cannot diffuse into the dispersion. The polymer concentration determines the osmotic stress acting on the dispersion. The spacing between the macromolecules or vesicles is measured by X-ray diffraction (XRD). In this way, one obtains pressure-versus-distance curves. The osmotic stress method is used to measure interactions between lipid bilayers, DNA, polysaccharides, proteins, and other macromolecules [36]. It was particularly successful in studying the hydration... 

Functional properties of polysaccharides (formation of viscous dispersions and gek) are associated with the mutual interactions of their chains and interactions with other food components (especially water, proteins and Kpids). 

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