Fermented milk and preparation methods thereof

A fermented milk, comprising an extruded whey protein isolate (WPI)-inulin composition, wherein:

• the fermented milk is prepared by adding the extruded WPI-inulin composition into raw milk, wherein a mass-volume ratio (g/mL) of the extruded WPI-inulin composition to the raw milk is in a range of (1.0-3.5):
• 100;
• and the inulin in the extruded WPI-inulin composition accounts for 5% to 15% by weight of a total weight of the extruded WPI and the inulin;
• the fermented milk is prepared as follows:
• step 1, preparing the extruded WPI-inulin composition by mixing inulin with a whey protein extruded at a temperature within a range of 45-55° C.;
• step 2, adding sucrose and the extruded WPI-inulin composition into the raw milk, and uniformly mixing and stirring the sucrose, the extruded WPI-inulin composition, and the raw milk to obtain a material A;
• step 3, preheating, homogenizing, sterilizing, and cooling the material A to obtain a fermentation substrate;
• step 4, adding a fermentation agent into the fermentation substrate, filling the fermentation substrate in a container, and then performing heat-preserved fermentation, and ending the fermentation to obtain a material B;
• step 5, cooling the material B, and then refrigerating the material B to obtain fermented milk;
• wherein the preparing the extruded WPI-inulin composition in the step 1 specifically includes:
• S1, carrying out an extrusion pretreatment on whey protein at an extrusion temperature within the range of 45-55° C. to obtain extruded whey protein, then freeze-drying the extruded whey protein, and grinding the freeze-dried extruded whey protein into powder;
• and
• S2, dissolving powdered whey protein and inulin in deionized water at room temperature to obtain a composition solution after stirring, then freeze-drying the composition solution to obtain a freeze-dried composition, and grinding the freeze-dried composition into powder to obtain the extruded WPI-inulin composition.