Relation between viscosity and expansion starch extruded: role of amylose
1997
Patria, A. (Universitas Syiah Kuala, Banda Aceh (Indonesia))
Starch blends (Waxy corn/High amylose corn) with different amylose content were tested. Comparison of flow curves show that higher amylose contents led to higher melt viscosity under the same conditions of moisture and temperature and similar degradation. Expansion was then studied through the three indices: LEI, SEI, VEI. As a general trend, a decreased of SEI and VEI (10 to 2.5) is observed when viscosity only increased in a range from 200 to 1000 Pa.s, whatever the amylose content. These tendances confirm that the expansion limiting role of melt viscosity. Nevertheles, the model of bubble growth in a polymer melt (Kokini, 1992) could not be applied here since melt temperature had a negative effect on SEI Tentative interpretation relies on the negative correlation between SEI and LEI. When melt pressure becomes too low, bubble growth start in the die favouring longitudinal expansion. The elucidation of this mechanism would of importance since most recent work underline the role of longitudinal expansion in the density of extrudate cells, which, in turn controls its crispiness
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