D-glucans

This group of nonreducing glucose polysaccharides contains a preponderance of 1,4-a-D-glycopyranosyl linkages. The most ubiquitous representative is starch. 

Starch is considered to be a neutral molecule, but potato starch has a low degree of phosphation and is thereby endowed with weak polyelec-trolytic character. Starch phosphate esters reside principally in the amylopectin fraction. 

Qu and Wang (1991b) ascribed sensorial appeal to the melting of starch granules and the ratio of gelatinized to melted starch. Other factors to consider are pH, oral stress, temperature, and concentration (Olkku, 1978). 

For mechanical stability against hydration and swelling, starch is chemically crosslinked (by adipic acid-acetic anhydride, phosphate, etc.) below Tgz, so that the physical integrity of the granules is not impaired by gelatinization. Weakly crosslinked starches (DS 0.1) are acid-stable and thus find occasional application in recipes containing vinegar. The many industrial functions of crosslinked starch include use as an adhesive. 

Substituent groups have been incorporated into dry or suspended starch, mainly to improve its properties and to stabilize it against retrogradation dispersion clarity is enhanced by substitution (Wurzburg, 1995). 

Subsequent to publication of an earlier article,1 several enzymic procedures have been applied to studies on aspects of the structures of (1 - 4)-(1 - 6)-a-D-glucans. 

Partial hydrolysis with alpha amylase (EC 3.2.1.1), followed by gel chromatography, has been used to study aspects of the physical structures of the amylose complexes formed with such organic compounds as 1-butanol, and of retrograded amylose. Differences were detected.387b 

When the / -limit dextrin of waxy-maize starch reacted with exo-maltohexahydrolase (EC 3.2.1.98), which can by-pass some a-(l- 6) linkages, the branched a-D-gluco-oligosaccharides expected, namely, 64-a-maltosylmaltopentaose (102), 63-a-maltotriosylmaltotetraose (103), 64-a-maltosylmaltohexaose (104), and 63-a-maltotriosylmaltopentaose 

There have been several examinations of the structure of Nageli dextrin,405407 which is prepared by the prolonged action of acid on granular starch. In one study,405 there was separated from waxy maize a branched fraction that was resistant to pullulanase action. As this fraction contained some molecules having two branch points that were in close proximity, it was considered that this may have hindered hydrolysis, and that it could be of relevance to studies on the structure of the original amylopectin. 

In view of the close association of peptide with acid-insoluble mammalian-muscle glycogen that had been subjected to proteolysis, the possibil- 

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PuUulan [9057-02-7] first described in detail in 1959, is a water-soluble extracellular a-D-glucan elaborated by the fungus yiureobasidiumpullulans (formerly Eullulariapullulans) (285). It is a linear polymer of maltotriose units linked from the reducing end of one trisaccharidic unit to the nonreducing end of the next trisaccharidic unit by a(l — 6) linkages (286) ... 

Chitosan, having a similar chemical backbone as cellulose, is a linear polymer composed of a partially deacety-lated material of chitin [(l-4)-2-acetamide-2-deoxy-/3-D-glucan]. Grafting copolymer chains onto chitosan can improve some properties of the resulting copolymers [48-50]. Yang et al. [16] reported the grafting reaction of chitosan using the Ce(IV) ion as an initiator, but no detailed mechanism of this initiation has been published so far. 

Curdlan possesses anti-tumour activity similar to that shown by fungal (1-D-glucans, a property which appears to be related to the ability to form triple helices. 

Echinocandins (i.e. caspofungin), semisynthetic lipo-peptides, inhibits the synthesis of (3-(l,3)-D-glucan, an... 

Fig. 22.—Antiparallel packing arrangement of the 2-fold helices of (1— 3)-a-D-glucan (21). (a) Stereo view of two unit cells approximately normal to the aoplane. The two chains in the back (open bonds) are antiparallel and so are the chains in the front (filled bonds). Each helix is stabilized by 2-OH 0-4 hydrogen bonds across the bridge oxygen atoms. Interchain hydrogen bonds are formed in sheets along the a direction, (b) An axial projection of the unit cell shows that the sheets in the front and back are also joined by hydrogen bonds.

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