ABSTRACTThe effect of the specific mechanical energy (SME) during extrusion of a protein‐starch mixture was studied by analyzing the glass transition temperature (Tg) and starch gelatinization. We found that the SME values of 344 to 2108 kJ/kg did not significantly change the Tg of the product. 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 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 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.