Amylose water-soluble

Starch is not a single molecule but a mixture of amylose (water-soluble, blue color with iodine) and amylopectin (not water-soluble, violet color with iodine). The composition is amylose 10-20%, amylopectin 80-90%. 

As a thickener (as opposed to a gel), it is amylose that has the main function. The long water-soluble chains increase the viscosity, which doesn t change much with temperature. Amylose chains tend to curl up into helixes (spirals) with the hydrophobic parts inside. This allows them to trap oils, fats, and aroma molecules inside the helix. 

Figure 17-5. Amylose, cellulose. Amylose consists of a water-soluble portion, a linear polymer of glucose, the amylose and a water-insoluble portion, the amylopectin. The difference between amylose and cellulose is the way in which the glucose units are linked. In amylose, a-linkages are present, whereas in cellulose, p-linkages are present. Because of this difference, amylose is soluble in water and cellulose is not. Chemical modification allows cellulose to become water soluble.

Addition of an aqueous solution of PEG to a saturated aqueous solution of a-CD at room temperature did not lead to complex formation unless the average molecular weight of PEG exceeded 200 [46]. Moreover, carbohydrate polymers such as dextran and pullulan failed to precipitate complexes with PEG, and the same was true for amylose, glucose, methyl glucose, maltose, maltotriose, cyclodextrin derivatives, such as glucosyl-a-CD and maltosyl-a-CD, and water-soluble polymers of a-CD crosslinked by epichlorohydrin. These facts suggested to Harada et al. the direction for further research. 

These water-soluble molecules are cyclic oligomers of a-D-glucose formed by the action of certain bacterial amylases on starches (Bender and Komiyama, 1978 Saenger, 1980 Szejtli, 1982). a-Cyclodextrin (cyclohexa-amylose) has six glucose units joined a(l, 4) in a torus [1], whereas /3-cyclodextrin (cycloheptaamylose) and y-cyclodextrin (cyclooctaamylose) have seven and eight units, respectively. 

High temperatures can break native S-S bonds and form new S-S bonds which can lock the protein into a denatured eonfiguration [89]. Low pH, sodium dodecyl sulfate. Tween 80, chaotropie salts, and exogenous proteins have been used to protect proteins from thermal inaetivation [90]. Ethylene glycol at 30-50% was used to protect the antiviral activity of P-interferon preparations [91]. Human serum albumin was used in recombinant human interferon-Psei-n which resulted in increased thermal stability [62]. Water-soluble polysaeeharides sueh as dextrans and amylose [92], as well as point-specific (site-directed) mutagenesis [93] have also been used to increase thermal stability of therapeutie proteins and peptides. 

Amylopectin Amylopectin is similar to amylose except that the glucose chain has branches. These branches involve linkages at the -CH2OH position ( 6), which makes them a 1 —> 6 linkages. Amylopectin is water-soluble it also interacts with iodine to form a reddish-purple complex. Typically, amylopectin is ten times the size of an amylose molecule. Digestion requires (3-amylase (1 4 linkages) and a second... 

PrObtom 22.42 The polysaccharide amylose, the water-soluble component of starch, is hydrolyzed to ( + )-maltose and D-(-t-)-glucose, Methylated and hydrolyzed, amylose gives mainly 2,3,6-tri-O-methyl-D-glucopyranose. Deduce the structure of amylose. 4... 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

Starch comprises a large percentage of cereals, potatoes, corn, and rice. Complete hydrolysis of starch yields glucose, but partial hydrolysis gives maltose as well. This shows that starch is a polymer of glucose units, joined by a-glycosidic linkage. Starch can be separated into two mam fractions by treatment with hot water. The insoluble component (10 percent to 25 percent) is amylose, the soluble... 

Because of the good x-ray data (a total of 99 intensities were available for refinement), difference Fourier techniques, such as described by Winter in this volume (33), could be used to locate the KOH and water molecules in this crystal structure. As shown in Fig. 6, the K " ion coordinates with four oxygens of the amylose chain and two water molecules. All three water molecules participate in hydrogen bonds, but the intermolecular hydrogenbonding pattern is not extensive. This probably accounts for the water-solubility of the complex. 

Fig. 16.—Mass, Q (mg/mL), of water-soluble products as a function of the content of amylose in starch. Variety of starch P, potato AM, amylomaize M, maize R, rice H, haricot bean MN, manioc WM, waxy maize B, bread wheat. Point P relates to potato starch after correction of the result attributable to high water content in that source (from Ref. 102).

Plants use starch granules for storing energy. When the granules are dried and ground up, different types of starches can be separated by mixing them with hot water. About 20% of the starch is water-soluble amylose, and the remaining 80% is water-insoluble... 

---