Amyloses recrystallization

Sodium propionate is also often used as an antifungal agent. Calcium is often preferable to sodium, both to reduce sodium levels in the diet and because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread, making them available for the yeast, and improving the texture of the bread. Stale bread is caused by the starch amylose recrystallizing. The enzyme a-amylase converts some of this starch to sugars, which helps prevent recrystallization. 

As discussed above, linear alkyl chains such as the fatty acid moiety of monoglycerides can form a complex with helical segments of the solubilized starch molecules. The recrystallization of amylose is apparently little affected by complexation with mono glycerides. Differential scanning calorimetry (DSC) studies of day-old bread crumb show that all the amylose seems to be present in a crystalline state. Complex formation with monoglyceride by the short side chains of amylopectin, however, markedly slow the rate of retrogradation. The half-life for reformation of amylopectin crystals (measured by DSC) is increased twofold to threefold when... 

When the A-fraction from corn starch is potentiometrically titrated with iodine, its affinity for the latter is sharply reduced in the presence of small amounts of fatty acid. Thus the iodine adsorption of recrystallized A-fraction (originally 18.7%) is reduced to 12.4%, 3.5% and 0% by the addition respectively of 2%, 5% and 10% of palmitic acid. Raw corn starch contains approximately 0.66% of fatty acids, corresponding to approximately 2% on the basis of the linear A-fraction. Thus, a third of the linear component in raw com starch is inactivated. In a sense, Taylor and coworkers were correct in assuming an association between a-amylose and fatty acid, but they erred in presuming the combination to be an ester. 

Table VI shows the results of a number of these experiments, using different magnesium sulfate concentrations. The increase of fractionation efficiency with increase of the salt concentration is evident. Independent of the salt concentration, all experiments yield amylose fractions of maximum iodine-absorption capacity, as recrystallization with 1-butanol did not show any increase in the original values.

Tukomane, T., and Varavinit, S. (2008). Classification of rice starch amylose content from rheological changes of starch paste after cold recrystallization. Starch/Stdrke, 60, 292-297. 

Cyclodextrins are degradation products from starch by the bacterium Bacillus macerans. They are separated by precipitation with complexing agents and purified by recrystallization. They could probably be produced industrially by the tonne. The formation of cyclodextrins is interpreted as a trans glycosidation of amylose under enzymic control. The latter, in aqueous solution, adopts at least partially the shape of a helix with a period of six glucopyranose units. The bacterial enzyme catalyses the junction of two glucopyranose residues separated... 

Starch is a polysaccharide formed by two polymers of glucose linear amylose and branched amylopectin. The gelatinization process can be regarded as a fusion of fhe crystalline starch regions in the presence of enough wafer and heafing. Starch retrogradation is a recrystallization process that is controlled by diffusion and depends on solute mobility in the system. 

Waxy corn (WCN30G30W) materials are amorphous after moulding at a temperature above 120°C. Potato starch materials (PN30G30W) show B-type crystallinity. The relative crystallinity (compared to native potato starch) decreases from 68% (at 110°C) to 36% (at 140°C). Above 140°C the relative crystallinity increases to a value of 70% at 190°C. These values are in agreement with values previously reported.14 It has been shown that the total B-type crystallinity of potato starch plasticized with glycerol and water can be considered as a summation of residual amylopectin crystallinity and recrystallization of both amylose and amylopectin depending on processing conditions. 

Kerr and Severson have superimposed selective precipitation on aqueous extraction technique, by treating the soluble extract with butyl alcohol. This gives an A-fraction (designated by Kerr as crystalline amylose ) of exceptionally high iodine adsorption, but in yields amounting to only 5-6% of the starch. The products from corn and tapioca starches analyze 20.5% and 20.7% iodine adsorption respectively, as compared with a maximum value of 19.0% after four recrystallizations of the Pentasol-precipitated A-fraction from corn starch. This suggests that the A-fraction may be somewhat diversified in molecular size, and that aqueous extraction preferentially dissolves the shorter linear chains. It is not to be expected that all the molecules of a natural high polymer should be of uniform size. 

In other instances, it is the solvent of crystallization which plays a decisive role in orienting the crystallization toward one or the other polymorph. Such solvent dependant crystallization is well documented in the case of amylose (7) where minute changes in solvent/precipitant ratio have a dramatic effe ct on shifting the recrystallized amylose among three polymorps amylose A,B and V. 

Indigestible dextrin [136] wheat albumin [5] bean extract (Hassler 2002) arabinose (Hassleretal. 2004) guava leaf polyphenol (Hassleretal. 2004) resistant recrystallized amylose (Hassleretal. 2004)... 

Besides plasticizer features, properties of the starch itself such as the amylose/ amylopectin ratio, also have an influence on the final material. As mentioned above, amylose and amylopectin recrystallize in different ways. Amylose will form the more crystaUine part of a thermoplastic and amylopectin the amorphous component the opposite behavior is found in the native starch granule, in which amylopectin is predominantly the crystalHne part. The source of the starch determines the ratio and the molar mass distribution of amylose and amylopectin, and consequently the properties of the thermoplastics made out of it [7]. In this chapter the effects of and relations between the plasticizer, the amylose/amylopectin ratio, and the mechanical properties of four starches from different sources-potato, pea, wheat, and waxy maize-are described and discussed. Besides an overview of the properties, this should finally lead to better insight into the behavior of starch materials during processing. 

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