Effect of specific mechanical energy on properties of extruded protein-starch mixtures

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 6.7x10(4). 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.