concluded that the high temperature in the extrusion processing caused most of the water soluble protein to break into small subunits, or become insoluble, and/or be redistributed. This phenomenon may cause to decrease the water solubility index with increasing temperature and soy protein isolate. Different results indicate that the key factor that affects the WSI is how much of the water soluble protein turns into water insoluble. In this study it has been shown that, at the lower temperature condition, increasing water content will increase the starch gelatinization and the protein denaturation, but when the temperature is higher to 180 C, the water soluble protein begin to break into insoluble subunits hence the adding water content resulted the decrease of the WSI. Fig. 4.