Abstract: Extrusion cooking is a high-temperature and short-time food processing technology, which can change the characteristics of purple sweet potato flour, thus improving the quality of composite dough with wheat and purple sweet potato flours. Therefore, the effects of adding extruded purple sweet potato flour (EPSP) versus non-extruded purple sweet potato flour (NEPSP) on water distribution, gelatinization and thermomechanical properties of wheat dough were investigated in this study. Results revealed that compared with NEPSP, EPSP significantly reduced the transverse relaxation time T21 (P < 0.05), indicating that EPSP could promote tight binding of water to starch or gluten. Moreover, compared with wheat flour, addition of purple sweet potato flour especially EPSP substantially decreased the peak viscosity, trough viscosity, final viscosity, setback value and breakdown value of dough (P < 0.05). The thermomechanical properties demonstrated that EPSP increased the water absorption, enzymatic hydrolysis rate and cooking stability (P < 0.05), and decreased development time, setback value and peak torque (P < 0.05). These results indicated that EPSP addition could not only increase the yield of dough, but also delay the aging of dough and extend the shelf life of the final product. This study provides a theoretical basis for the application of EPSP in wheat products.

Key words: purple sweet potato flour, extrusion, water distribution, pasting properties, thermomechanical properties