Methods for extracting milk protein from expired or spoiled milk

A method for extracting protein from milk comprising the steps of:

• a) mixing the milk with a 1-10% acid solution to a mass ratio of 2:1 to 5:1, thereby forming a milk solution;
• sterilizing, deodorizing and dissociating protein;
• b) coarse filtering the milk solution through a single layer of gauze to remove bacteria and impurities to obtain a stock solution;
• c) filtering the stock solution with a filter cloth to remove hyphae, denatured proteins and solid jelly to obtain a filtered stock solution;
• d) transferring the filtered stock solution to a container;
• e) adding a sodium hydroxide solution to the filtered stock solution to reach a pH of between 7 and 9;
• f) adding an activator to the filtered stock solution for protein activation;
• g) adding a dilute acid solution dropwise to the filtered stock solution, thereby causing the dissociated protein to self-assemble, complex and salt out to obtain a regenerated milk protein;
• h) defatting the regenerated milk protein with a degreasing agent;
• i) washing and filtering the milk protein to obtain a skim milk protein;
• and
• j) drying the skim milk protein.