Starch crystalline forms

Dissolve 34 g. of o-nitroaniline in a warm mixture of 63 ml. of concentrated hydrochloric acid and 63 ml. of water contained in a 600 ml. beaker. Place the beaker in an ice - salt bath, and cool to 0-5° whilst stirring mechanically the o-nitroaniline hydrochloride will separate in a finely-divided crystalline form. Add a cold solution of 18 g. of sodium nitrite in 40 ml. of water slowly and with stirring to an end point with potassium iodide - starch paper do not allow the temperature to rise above 5-7 . Introduce, whilst stirring vigorously, a solution of 40 g. of sodium borofluoride in 80 ml. of water. Stir for a further 10 minutes, and filter the solid diazonium fluoborate with suction on a sintered glass funnel. Wash it immediately once with 25 ml. of cold 5 per cent, sodium borofluoride solution, then twice with 15 ml. portions of rectified (or methylated) spirit and several times with ether in each washing stir... 

Longer carbon chains can also be added, such as carboxyethyl groups, or carboxypropyl groups. Adding bulky functional components like carboxymethyl and carboxyethyl groups reduces the tendency of the starch to recrystallize. When the starch stays as a gel, a product is softer, and we refer to it as fresh. When the starch regains its crystalline form, the product becomes firmer, and we refer to it as stale. The technical term for this recrystallization is starch retrogradation. 

The only pectic enzyme thus far obtained in crystalline form is the endo-D-galacturonanase from Acrocylindrium.209 Crystallization of the enzyme from a solution of ammonium sulfate was preceded by chromatography on calcium phosphate, Duolite CS 101, and DEAE-cellulose, and by starch-gel electrophoresis. 

Fig. 21.17. X-ray diffraction pattern of the cream, showing that SnC>2 is present (filled circles). The crystalline fatty acids (open circles) probably formed by deterioration of the animal fat component during burial. Starch is not evident and so must be in a non-crystalline form, consistent with mode of preparation. (Reprinted/redrawn from Nature, 432, 35-36, Copyright 2004, Nature Publishing Group, with permission.)...

This particular trimethylglucose is unique in that it was separated in crystalline form from the hydrolyzates of the methyl ethers of several naturally-occurring glucose polymers almost two decades before it was synthesized from glucose. These natural sources, which still furnish the most convenient routes for the preparation of 2,3,6-trimethyl-D-glucose, include maltose,124-128 cellobiose,127,128 lactose,122-181 starch,71,182 glycogen,188,184 cellulose,185-187 and lichenin. 188,189 The literature pub-... 

Starch crystallinity is caused by paraUely arranged starch polymers which act as crystals. No evidence has been presented in published literature to describe the actual physical nature of "starch crystallites." It should not be considered that starch granules contain "crystals" or "crystallite particles" formed by starch polymers. Starch crystallinity represents the relative arrangement of starch polymers in granules, not the presence of physical "crystals."... 

Cyclodextrins (CDs) were first observed by Villiers (i) nearly a century ago. First thought to be a mysterious crystalline form of starch, the structure and chemistry of these unique cyclic glucan oligosaccharides have been elucidated through the contributions of Schardinger, Freudenburg, Cramer and French (2). 

Sugar of Starch and Wood. — CrystaUizable out ninety per cent, in a crystalline form, he will return ... 

The pure oleoresin produced by solvents normally contains only pure curcumin, in a crystalline form. It is hardly soluble in liquid- and supercritical CO2- Even at an extraction pressure of 450 bar, and with 2 hours extraction time at 65°C, only 20% of the initial curcumin can be extracted. On the other hand, all the volatile oil and fatty oil is extracted, and a fat-free curcumin-starch mixture with a very low flavour-content can be produced. The total extraction yields are between 5 to 12%, with mostly fatty oil and volatile oil, and about 10% curcumin in the extract. 

Amylose, a linear, high molecular weight (l- -U)-a-D-glucan, is one of the principal polysaccharides of starch. Because of the longstanding utility of starch as a raw material, and its widespread botanical availability, its structure and properties have been studied for centuries. Since the more recent realization that almost all varieties of starch are composed of two polysaccharides - the linear amylose and the branched amylopectin - a significant share of interest has shifted to the study of these components. Of particular interest has been the observation that both components occur naturally in crystalline form in the starch granule. 

Figure 5.16 Schematic model for the arrangement of amylopectin in potato starch. Crystalline layers containing double helical linear segments in amylopectin molecules form a continuous network consisting of left-handed helices packed in tetragonal arrays. Neighboring molecules are shifted relative to each other by half the helical pitch. (Adapted with permission from reference 3)...

There are at least four crystalline forms of cellulose, based on different packing of the primary chain (Blackwell, 1982), and three forms of granular starch, based on the packing of double helices (Noel et al., 1993). The differences are largely in the unit-cell dimensions and the crystallization and precipitation temperatures. One form of starch, precipitated with alcohol, is in a symmetrical molecular arrangement and is readily dispersible in cold water (Kerr, 1950). Mannan and dextran yield different crystals at low and high temperatures, and there was not only a polymorphic difference, but a conformational difference in cellulose (Quenin and Chanzy, 1987). Curdlan appears to have three polymorphs—anhydrous, hydrated, and annealed. 

Probably the most important components in foods that crystallize are water, sugars (and sugar alcohols) and fats. However, salts, organic acids, starch, emulsifiers, and even proteins may be found in crystalline form in certain foods. 

Salts of primary aromatic amines react with nitrous acid to produce diazonium salts. The reaction is usually performed by adding a cold solution of sodium nitrite to a cold solution of the arylamine in aqueous mineral acid. The end point of the reaction is conveniently determined by the detection of excess nitrous acid with potassium iodide-starch paper. Sulfamic acid has long been used both in industry and in the laboratory to remove excess nitrous acid. It has been found to react with the more active diazo compounds. In most cases, high temperatures are avoided to prevent the formation of phenols and the decomposition of the unstable nitrous acid. An excess of mineral acid is necessary to prevent coupling between the diazonium salt and unreacted amine (cf. method 494). If the amine salt is somewhat insoluble, a fine crystalline form, which is produced by rapid crystallization from a warm aqueous solution, may be employed. ... 

As originally reported, selective precipitation of the A-fraction was accomplished by saturating a starch paste with butyl alcohol, then autoclaving for 2-3 hours at 18-20 lb. pressure. On cooling to room temperature, the A-fraction separated in characteristic crystalline form and could be collected by supercentrifuging. The yield was 22-23% frona either corn or potato starch. The iodine adsorption of the crude precipitated A-fraction was 16.5% for the non-precipitated B-fraction it was 1.5-1.7%. 

Wiegel has reported the isolation of A-fraction in approximately 10% yield by leaching potato starch with boiling 30-35% ethyl alcohol. On treating the soluble extract with such precipitants as butyl or isobutyl alcohol, the A-fraction separates in characteristic crystalline form. 

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