Shear induced starch conversion during extrusion.
1994
Zheng X. | Wang S.S.
Using a capillary rheometer and a single-screw extruder, waxy corn starch was extruded at a relatively low temperature range. Notable conversions induced by shear energy were obtained in very short residence times (from several sec to 1 min). Conversions up to > 70% were also achieved. Kinetic studies showed that conversion caused by shear energy was more efficient than that by thermal energy. The shear rate constant, ks, was an exponential function of shear stress and a linear function of shear rate. The minimum shear stress required to cause starch conversion was from 10(4) to 10(6) N/m2 for 100 degrees C to 21 degrees C. In such "shear" experiments, the maximum temperature rise due to viscous thermal dissipation, measured experimentally and calculated theoretically, was too low to cause any significant thermal cooking of starch. The shear converted starch extrudates were unpuffed and had shapes of traditional pasta.
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