GELATINIZATION OF STARCH AND MECHANICAL PROPERTIES OF STARCH PASTES
1984; Elsevier BV; Linguagem: Inglês
10.1016/b978-0-12-746270-7.50015-x
Autores Tópico(s)biodegradable polymer synthesis and properties
ResumoCereal grains, tubers, and roots are the main sources of starches for industrial and consumer applications. Following synthesis, starch is stored in the plant as compact micron-sized granules that are partly crystalline and, hence, water-insoluble, facilitating starch isolation and handling. The first step in starch utilization disrupts the granular structure leading to granule swelling and the hydration and solubilization of starch molecules. These events, collectively referred to as starch gelatinization, are affected by heating the granules that are slurried in water. For thickening foods, sizing and coating papers, sizing textiles, use in drilling muds or adhesive formulations, and use in a host of other applications, starch gelatinization in aqueous media is the first step. When starch is cooked, the flow behavior of a granule slurry changes because the suspension becomes a dispersion of swollen granules, partially disintegrated granules, and molecularly dispersed granule contents. The cooked product is called a starch paste. Transition from a suspension of granules to a paste is accompanied by a large increase in apparent viscosity. During cooling, paste consistency increases as molecular association forms a cross-linked network that increases paste resistance to deformation. In a cooled state, pastes may remain fluid or form a semi-solid or solid gel showing considerable strength.
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