Starch hydratation process

A commercial fractionation process in which groats are dry-milled and the comminuted groats are soaked in a solution of cellulases and hemicellulases has been developed.9 In addition to the starch the process produces fiber and protein fractions. Unlike wheat starch, oat starch cannot be separated from the grain by selective hydration and centrifugation, because of hydrated bran and protein layers. 

The irradiation of starch in aqueous gels, sols, and solutions leads to somewhat different results because of the operation of different mechanisms. Although all reactions in the solid state involve free-radical processes, those in aqueous solutions may involve hydrated electrons, which with oxygen give O2 ions. Kochetkov et al. 90 have assumed that deoxy sugars result from the involvement of Oj ions alone, whereas the formation of deoxy ketoses is assisted by hydroxyl radicals. Stockhausen et a/.191 have proposed the following sequences of reactions. Ionization of water leads to solvated electrons and further radicals. 

Starch changes during cooking of pasta are reported to vary from a hydration-driven gelatinization process in the outer layer to a heat-induced crystallite melting in the center.525 It is speculated that both the state of the starch and the surface structure contribute to the development of the elastic texture and stickiness of pasta. Interactions between starch and the surrounding protein matrix are evident in the outer and intermediate layer. In the center of cooked pasta, wheat starch granules retain their shape due to limited water diffusion, and the protein network remains dense. 

Proteins, lipids and phosphorus are the minor non-carbohydrate components of barley starch. These components have been shown to influence hydration rates, thermal properties, retrogradation characteristics, rhelogical characteristics, susceptibility towards a-amylolysis and processing, and product qualities of starch hydrolysates. 

Multivalent ions in starch dispersions, particularly those of aluminum, calcium, sulfate and oxalate, will induce retrogradation due to complexation or competition for water of hydration. The ions can be introduced by hard process water or accumulate by leaching from paper during surface sizing or coating. The destabilizing effect of ions follows the Schulze-Hardy rule. 

In order for starch molecules to become detached from one another, they must be hydrated, a process accomplished in water slurry by using either thermal or chemical energy. Only then will the molecules be separated and uncoiled enough to be able to latch onto other separate particles and act as an adhesive. The most common form of chemical hydration of starch is through the use of aqueous alkali. Sodium hydroxide is capable of hydrating starch molecules without heat, but a specific minimum concentration must be reached for that to occur (2). 

Figure 39 illustrates the effects of some anions on those processes. For example, anions that are poorly hydrated are adsorbed more strongly on the surfaces of starch micelles. The salts that are adsorbed in a polar manner bring water with them, since they are strongly hydrophilic and thereby... 

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