Polar starch

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. 

The GBR resin works well for nonionic and certain ionic polymers such as various native and derivatized starches, including sodium carboxymethylcel-lulose, methylcellulose, dextrans, carrageenans, hydroxypropyl methylcellu-lose, cellulose sulfate, and pullulans. GBR columns can be used in virtually any solvent or mixture of solvents from hexane to 1 M NaOH as long as they are miscible. Using sulfonated PDVB gels, mixtures of methanol and 0.1 M Na acetate will run many polar ionic-type polymers such as poly-2-acrylamido-2-methyl-l-propanesulfonic acid, polystyrene sulfonic acids, and poly aniline/ polystyrene sulfonic acid. Sulfonated columns can also be used with water glacial acetic acid mixtures, typically 90/10 (v/v). Polyacrylic acids run well on sulfonated gels in 0.2 M NaAc, pH 7.75. 

Although the dipolar and resonating nature of the interaction of amylose and iodine is well established, Schlamowitz173 regards the iodine in a starch complex as being in a predominantly non-polar form, and Meyer and Bern-feld174 refute the helix theory and consider that adsorption of iodine occurs on colloidal micelles in amylose solutions. Most of the experimental facts which Meyer presents can, however, be satisfactorily explained on the helical model. 

Fig. 4 Sodium starch glycolate viewed (a) using ordinary illumination and (b) between crossed polarizers.

Gels used for the stationary phase can be hydrophilic, for separations in aqueous and other polar solvents, or hydrophobic, for use in non-polar or weakly-polar solvents. Agar, starch, polyacrylamide and cross-linked dextrans possess hydroxyl or amide groups and are thus hydrophilic. They swell... 

For maximum efficiency, methylation should be a single-phase reaction and so those methods employing aqueous alkali are most suitable for water-soluble compounds and the Purdie method for non-polar compounds. A carbohydrate which is initially soluble in water e.g., starch, dextran) may be less soluble when partially methylated and for this reason an inert solvent e.g., acetone, dioxane, carbon tetrachloride) is often introduced during the later stages of a methylation with dimethyl sulfate. It is interesting to note that methyl a-D-glucopyranoside forms a trithallium derivative which is insoluble in water and consequently the introduction of more than three methoxyl groups by the Menzies method... 

Starch granules, when observed imder polarized light, exhibit an optical birefringence pattern known as a "Maltese cross" (Fig. 5.4), which implies a high degree of molecular order within the granule (Greenwood, 1979). 

FIGURE 5.4 Potato starch granules viewed under polarized light (magnification, x400). Reprinted from Encyclopedia of Food Sciences and Nutrition (Second Edition), Jackson (2003b), Starch - Structure, properties and determination. Pages 5561-5567, with permission from Elsevier. 

For conventional or normal, in contrast with reversed-phase, LLPC, many materials have been used as the solid support for the stationary liquid. In addition to silica gel, which was the first and is still the most popular material, a variety of other adsorbents that adsorb the polar solvent such as cellulose powder, starch, alumina, and silicic acid have been used. The more recent practice of HPLC has greatly simplified the technique in providing column stability for repeated use and for treatment of large volumes. 

Conference is to review progress in sponsored research for solution of both pollution and the farmer s problems by blending com starch polymers with polyethylene (1,2). There are several problems in blending these two polymers of very different polarities. 

The surface polarity of telomerized starches was determined by the contact angle technique. The surface free energy of the solid was measured from the contact angles of a drop of various probe liquids with the surface of a starch tablet (Table 16). 

The DS has a strong influence on the hydrophobic character of the modified starches and, as expected, increasing the DS decreases the polarity of the surface. For DS > 0.1, contact angles are greater than 90° with quite a low total surface energy, indicating a significant hydrophobicity of the material and a low wettability as previously reported for esterified starches [74-76]. 

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