Abstract:The effects of soy protein isolate (SPI) on dough properties and the mechanism underlying the impact of SPI on wheat protein were investigated in this study. The results showed that as the amount of SPI added gradually increased, the wet gluten content and the gluten index displayed downward and upward trends, respectively. The water absorption rate, development time, stability time, and farinograph quality number of SPI-dough gradually increased, whereas the degree of softness gradually decreased. The tensile energy and extensibility of mixed dough gradually decreased, whereas the resistance to extension and the extension ratio gradually increased. Compared with the control, the peak viscosity and setback of mixed dough decreased upon addition of SPI. The total proton signal amplitude, T2(1) proton signal amplitude, and T2(2) proton signal amplitude gradually increased with SPI addition. The -SH and -S-S- contents gradually increased and decreased, respectively, upon addition of SPI. After comprehensive consideration, the optimum amount of added SPI in flour products should be under 7%. As can be seen from the results of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions, crosslinking between SPI and wheat protein did occur; in addition to disulfide bonds, other covalent bonds were also observed between SPI and wheat protein. These results provide a theoretical basis for adding SPI to improve the nutritional value and processing quality of flour products and expand the application of soybean protein in the processing of flour-based foods.
