Step 1: Mechanical degradation of protein-rich foods in the mouth.Step 2: Denaturation of proteins in the stomach by hydrochloric acid.Step 3: Breaking down the protein of food into peptides and some free amino acids in the stomach by the pepsin enzyme. Step 4: The resulting products (peptide-polypeptides) are passed into a duodenum. Here, the polypeptides are further degraded to the oligopeptides and amino acids by the trypsin enzyme.Step 5: In the small intestine, along with the last stages of degradation, begins the process of absorption of degradation products into the blood.