Improving the emulsifying properties of whey protein isolate-citrus pectin blends by a novel reactive extrusion approach

In this study we used a new experimental setup to improve the emulsifying capacity of whey protein isolate-citrus pectin (WPI-HMCP) blends during extrusion processing. In this setup, the extruder serves as pump, while the reaction takes place mainly in a 380 mm long slit die which is attached at the end of the extruder. Using this setup, it is possible to improve the emulsifying capacity of WPI-HMCP blends: The Sauter mean diameter of emulsions stabilized by the extruded blends could be reduced compared to those stabilized by the untreated blend. The smallest Sauter mean diameter was measured when the WPI-HMCP blend was treated at 120 °C for 46 s residence time in the reaction die (corresponding to a total mass flow rate of 19.4 kg/h). It was halved compared to the untreated blend. Structural analyses of the reaction products showed that at constant reaction die temperature and increasing total mass flow rate the formation of disulfide bonds is favored, while the formation of non-disulfide covalent cross-links is inhibited.