Disulfide linkages in proteins are covalent bonds formed between the thiol groups of two cysteine amino acid residues through oxidation, resulting in a cystine unit. These bonds stabilize the three-dimensional folding of proteins by locking secondary structures such as alpha-helices and beta-sheets into place, which is especially important for extracellular proteins exposed to varying environments. They are critical in biological molecules including insulin, antibodies, and keratin, where they maintain structural integrity and enable proper function. In food science and cooking, disulfide bonds influence protein behavior in dough elasticity, meat texture, egg white coagulation, and cheese formation; reducing agents like glutathione or heat can break them, altering food properties. The bonds are reversible under physiological conditions via enzymes such as protein disulfide isomerase.