Glycomacropeptide (GMP), also known as caseinoglycomacropeptide, is a 64-amino acid peptide (residues 106-169 of bovine κ-casein) released during rennet-induced cheese coagulation. It is heavily O-glycosylated with sialylated oligosaccharides, contributing to its bioactivity. GMP is low in phenylalanine, making it suitable for phenylketonuria diets, and exhibits prebiotic, antimicrobial, and immunomodulatory properties. It is highly water-soluble and used as a functional food ingredient in nutritional supplements and infant formulas. As a milk-derived peptide, it is generally recognized as safe (GRAS) with no significant toxicity reported in scientific literature.