Polysaccharide dispersion

These structures and conformations of polysaccharide molecules and their intermolecular associations give polysaccharide solutions, polysaccharide dispersions, and polysaccharide gels their special properties in biologic systems and in industrial usage. The ease with which polysaccharides dissolve is related to their conformation and structure in many the same ways as is their solution behavior. 

Cheese whey demineralization Desalting of protein hydrolysates (i.e., soy sauce), sugar solutions, molasses, and polysaccharide dispersions Deacidification of fruit juices Tartaric wine stabilization Flavor recover from pickle brines... 

Polysaccharides, remarkable for their water affinity, can embody many times their weight or volume of this solvent—hence the name hydrocolloids. Polysaccharide dispersions are either hydrosols, hydrogels, or xerogels (de-... 

As adsorbate, the polysaccharide dct is sensitive to the DP and polydis-persity (Cohen Stuart et al., 1982). Higher DP polysaccharides are less kinetically active, are therefore slower to accumulate than lower DP polysaccharides because of the time taken for surface orientation, and are thus more inclined to stay adsorbed longer and reach higher concentrations. Agitation increases the rate of physical adsorption. From the foregoing discussion on polysaccharide dispersibility, it is safe to conclude that multilayer adsorption is antecedent to polysaccharide phase inversion and in some instances to sol-gel transition. 

The total energy content (E) of an aqueous polysaccharide dispersion is stated in the general equation... 

For polysaccharide dispersions, SV is exceedingly small relative to Vi. Equations (3.11) and (3.12) are mathematical propositions that the exchangeable energy stored in a dispersed polysaccharide solute is equal to the energy absorbed from an external source and any increase in surface area of the solute is consequently a repository of +A . Conversely, aggregation and desorption correspond to a loss of energy, felt as heat in the latter occurrence ( —A ) when a dry polyaccharide powder is wetted (positive adsorption). 

AH, AS, and AG may help to elucidate a mental picture of events, the thermodynamic status of most polysaccharide dispersions depends on the processes it underwent to achieve a desired end-product or use. 

T is the defining parameter of both the thermodynamic and kinetic states of polysaccharide dispersions. With declining T, T increases and vf decreases until Vj = 0 when all macromolecular motion ceases and the dispersion becomes essentially frozen with the onset of brittleness. With increases in T, the hydrogen-bond strength decreases, a poor solvent may become good, and a good solvent may become better. The strength of the hydrophobic bond increases with T (Ben-Naim, 1980). 

At 1-atm pressure in the surroundings, polysaccharide deformation and flow are normally initiated either by gravity or an applied shear rate (y) solvent (water) only flows under temperature (T) and concentration (c,) gradients. When T)i is constant or independent of the rate of shear (y in s 1) or stress (t), the flow is Newtonian. Very dilute polysaccharide dispersions are characterized mostly by Newtonian flow. At moderate concentrations, ti, may decrease (shear-thinning synonymous with pseudoplastic) or increase (shear-thickening synonymous with dilatant) nonlinearly with y for these dispersions, is replaced with (the apparent viscosity). Low DP and uniform distribution of substituents are conducive to tH high DP and nonuniform distribution are conducive to. A high T a is believed to elicit the human oral sensation of thickness. ... 

In polysaccharide dispersions, a constant-temperature, constant-pressure separation of any or all of the solute from its dispersion medium may be effected spontaneously by time (aging) or may be actuated by external... 

Polysaccharide dispersions phase-separate spontaneously, a phenomenon called aging. Phase-separation may be induced in special systems, under controlled conditions (e.g., encapsulation), to industrial and commercial advantage. 

Ratio of Intrinsic Viscosity of Polysaccharide Dispersions Heated (Enr ]fc) for 15 min at I2I°C and the Corresponding Unheated ([i)]c) Controls"... 

For practical reasons in a food plant where advanced instrumentation is not always available, it is desirable to have recourse to simple techniques to assess quality. Any property of a polysaccharide dispersion can do this if quality factors are adequately referenced. 

Food-grade CMC is a cellulose carboxylic acid ether with an optimum DS = 0.4-0.7. The higher the DS within this range, the more hydrophilic is the polyanion. Uniformity of substitution makes CMC more compatible with dissolved salts and less inclined to thixotropy than uneven distribution (Feddersen and Thorp, 1993). This gum does not precipitate from a 50% ethanol solution. Below approximately pH 4 in water, the polyanions revert to the un-ionized, water-insoluble acid. CMC viscosity-hysteresis has already been described (Fig. 2 in Chapter 3). CMC dispersions and films have the extra advantage of transparency relative to many other polysaccharide dispersions. The films are resistant to oils, grease, and organic solvents (Hercules, Inc., 1980). 

The above equation was also applicable to stickiness, S, substituted in place of the thickness, T. Because Cutler et al. (1983) have shown that perceived thickness and viscosity were linearly related, the correlations for perceived thickness can be used for perceived viscosity. By combining Equations 7.1 and 7.3, one obtain an expression to calculate the viscosity 7n of aNev nonian liquid that would be perceived as having an identical thickness and stickiness to any polysaccharide dispersion with known and ]>o.i ... 

Many semisolid food materials portray yield stress. The yield stress in polysaccharide dispersions results from intermolecular hydrogen bonding and molecular entanglements (Gencer, 1985). A precise quantitative knowledge of yield stress is necessary since it is very important in pumping operations, stability of suspensions, appearance of coated materials, and consumer acceptability (Kee and Duming, 1990). 

Degradation of the polysaccharide during methylation can be minimized by performing the reaction at low temperatures and in an atmosphere of nitrogen. Methylation is facilitated by simultaneous deacetylation and methylation of the polysaccharide acetate dispersed in an inert solvent IJiS), Fully methylated polysaccharides are obtained only after repeated methylations, which are often completed by a final methylation with a mixture of silver oxide and methyl iodide. Resistant hydroxyl groups may be methylated by the alternate addition of sodium metal and methyl iodide to the polysaccharide dispersed in liquid ammonia... 

Polysaccharide Dispersion concentration (% w/w) Dynamic viscosity (mPa/s) Polysaccharide Dispersion concentration (% w/w) Dynamic viscosity (mPa/s)... 

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