Functional properties modification of extruded soy protein concentrate using neutrase

Enzymic hydrolysis of extruded soy protein concentrate with Neutrase was used for the preparation new soy protein products with modified functional properties. After the determination of optimum values of pH as 6.8; temperature as 50degreesC, and water addition as 13.3 kg/kg protein, the response surface methodology with enzyme: substrate ratio and time as independent variables was used to establish optimal conditions of the process. Solubility, water holding capacity (WHC), back extrusion work (BEW) as well as emulsifying (BAI, ESI) and foaming (170) properties were taken as optimisation criteria. It was found difficult to obtain an ideal product by combining all the best features due to the multidirectional effect of hydrolysis on the changes of various functional properties. Nevertheless, optimal hydrolysate can be obtained at relatively low additions of Neutrase to the extrudate (e.g., 18 mAU/g protein) and in short time (e.g. 60 min). Under such conditions, the process provides a product containing 0.8 mmol amino nitrogen/g protein, which combines the features of a protein hydrolysate and those of an extrudate. SDS-PAGE of the optimal hydrolysate revealed that proteolysis of the extruded concentrate was more extensive than proteolysis of its counterpart which was not subjected to extrusion.