Insight into Sequential Extrusion and Cysteine Treatment for Improving Rheological Characteristics and In Vitro Digestibility of Whey Protein Isolate

The effects of sequential cold extrusion and cysteine (Cys) treatment on the rheological characteristics and in vitro digestibility of whey protein isolate (WPI) were researched in this work. Cold extrusion and Cys treatment increased the apparent viscosity, shear stress, Péclet number, and viscoelasticity of WPI. Furthermore, the emulsifying activity index enhanced in the order of WPI, Cys-treated WPI (Cys-WPI), cold-extruded WPI (CWPI), and extrusion-Cys treated WPI (Cys-CWPI). The emulsion stability index of Cys-CWPI was increased by 29.69% higher than that of WPI. Besides, the α-glucosidase inhibitory rate and xanthine oxidase inhibitory activity in the digests of Cys-CWPI were markedly increased compared with digests of WPI. The synergism of cold extrusion and Cys provides an effective approach for the application of whey protein-based thickeners and emulsifiers; meanwhile, its digestive products may assist in the development of hypoglycemic and uric acid-lowering foods.