Techno-functional properties of the starch-protein interaction during extrusion-cooking of a model system (corn starch and whey protein isolate)

Techno-functional properties of the starch-protein interaction were investigated during extrusion-cooking of a model system (corn starch (CS) and whey protein isolate (WPI)). A single screw extruder was used at a speed of 200 rpm, feed rate of 100 g/min, extrusion temperature of 140 degrees C and feed moisture content of 20%. The results showed that the extrusion process increased the water absorption index and caused a decrease in the water solubility index, except in the CS/WPI (100/0) formulation. Extrusion decreased the oil absorption capacity of the 50/50, 25/75 and 0/100 blends, while it had no apparent effect (P > 0.05) on the 100/0 and 75/25 blends. The emulsifying capacity in the extruded blends ranged from 34.07 to 44.67%. The value decreased as the amount of WPI increased, and in the raw blends, it ranged from 36.32 to 53.14% with the same trend. The gelling capacity of the CS was improved and that of the WPI decreased after extrusion. Extrusion caused an increase in bulk density, and a double increase in foaming capacity was observed in the 25/75 and 0/100 blends. These findings reveal the importance of extrusion in the interactions generated between CS and WPI that may lead to improvements in its techno-functional properties.