Starch Conversion

When the starch granule is heated in the presence of an adequate or excess amount of water, gelatinization of starch takes place. Several steps are associated with gelatinization, such as hydration and swelling of granules, heat absorption, and the loss of crystallinity as judged by the disappearance of both optical birefringence and X-ray diffraction pattern. In the extrusion cooking of starch containing materials, starch is heated under high pressure, shear force, and a limited amount of water, to say less than 40%. At a high enough temperature and low moisture content (17,18), starch granules undergo both gelatinization and melting processes. Thus, starch conversion duringfood processing is not an elementary reaction as discussed before. The conversion itself is a complex phenomenon that is further complicated by heat, mass, and momentum transfer in a reactor like an extruder. The kinetics studies on starch conversion, and other similar processes, take the advantage of an overall rate approach and use the parameter percent conversion instead of concentration for the formulation of kinetics equations. Starch conversion is an en-dothermic reaction. The degree of conversion of starch during processing due to heat or shear can be evaluated by the decrease of the differential scanning calorimeter (DSC) endotherm area. This area is directly proportional to the mass of unconverted starch in the sample. The degree of conversion X can be defined as follows:

The Mediterranean Diet Meltdown

The Mediterranean Diet Meltdown

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