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Effect of Specific Mechanical Energy on Properties of Extruded Protein-Starch Mixtures

¹Food Science Department, Rutgers—The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ 08901. ²Corresponding author. E-mail: kokini@aesop.rutgers.edu Phone: 732-932-9611 ext 201.

The effect of the specific mechanical energy (SME) during extrusion of a protein-starch mixture was studied by analyzing the glass transition temperature (T_g) and starch gelatinization. We found that the SME values of 344 to 2108 kJ/kg did not significantly change the T_g of the product. To explain the insensitivity of T_g to SME in spite of reported fragmentation taking place during extrusion, we studied the effect of the molecular weight (MW) on T_g in a model system consisting of dextrans of varying molecular weights. We found that the effect of the molecular weight on the T_g reached a plateau at 6.7 × 10⁴. Because the reported size of the fragments created during the extrusion process is larger than this, we were able to explain the apparent insensitivity of T_g 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.