Gelatinization and Melting of Starch and Tribochemistry in Extrusion

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Abstract
Cooking of starch is traditionally achieved by supplying sufficient thermal energy to it as in baking and broiling processes. Whereas in extrusion cooking, both thermal and shear energy are usually present in doing the job. The relative importance of each of the two energy sources are difficult to assess in the process. The interactions between water and the anhydroglucose unit of the starch are discussed. The kinetics of starch conversion to cooked starch at excess or limited water contents are reviewed. Calorie per calorie, shear energy is more efficient in cooking starch than thermal energy. And shear energy alone, without thermal energy input, can cause cooking of starch if the energy level is high enough. In order to capitalize on the effect of shear energy on starch cooking, running the extruder at low temperatures, say lower than 50°C is recommended.