15D-10 |
The effect of specific mechanical energy on the properties of extruded protein/starch mixtures |
J. L. KOKINI and M. Gropper. Dept. of Food Science/Center for Advanced Food Technology, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901 Specific mechanical energy (SME) was reported to be responsible for fragmentation of starch molecules, as a result of the effect of shear forces on amylopectin molecules, which are broken mainly at the a-1:6 bonds. Based on this hypothesis, some researchers reported a decrease in the product’s glass transition temperature (Tg) with the increase of SME. In contrast to starch degradation, it was reported that proteins are more resistant to the shear forces and do not fragment during extrusion. The objective of this research was to study the effect of SME on the glass transition, gelatinization and microstructure of mixed protein/starch systems and to examine the validity of the degradation models in explaining the Tg vs SME results. The effect of specific mechanical energy during extrusion of a protein/starch mixture was studied by analyzing the product’s Tg and starch gelatinization. We found that the SME did not significantly change the Tg of the product in the SME range of 344 to 687 KJ/kg. In order to explain the insensitivity of Tg to SME in spite of reported fragmentation taking place during extrusion, we studied the effect of the molecular weight (Mw) on Tg in a model system consisting of dextrans of varying molecular weights. We found that the effect of the molecular weight on the Tg reached a plateau around 64kD. Since the reported size of the fragments created during extrusion process is larger than this, we were able to explain the apparent insensitivity of Tg to SME in the protein/carbohydrate matrix studied. However, we found that starch gelatinization varied with SME, the degree of gelatinization being higher for systems exposed to higher SME. The findings of this study contribute to a better understanding of the transformations that take place during food extrusion, enlarging the knowledge base in this challenging domain.
Session 15D, Food Engineering: Processing Technologies
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