Effects of the extrusion specific mechanical energy (SME) on the physicochemical properties including color parameters (L*, a*, b* and Delta E), textural properties (tensile strength, hardness, chewiness and degree of texturization), on-line viscosity at die, protein solubility, and the molecular weight distribution of texturized soy protein were investigated. A higher SME resulted in extrudates with lower L* but higher a*, Delta E, higher tensile strength, and hardness. The viscosity of dough at die decreased from 997.17 to 867.29 Pa s when SME increased from 819.70 to 1258.70 kJ/kg. The increasing SME also caused an increase of protein solubility in phosphate buffer solution by 15.30%. Increasing the SME resulted in higher content of low Mw subunits as well, which was evidenced by SDS-PAGE. It was concluded that increasing SME increased the proportion of smaller fractions, and led to darker and higher tensile strength products. (C) 2013 Elsevier Ltd. All rights reserved.