A Sialic Acid Assay in Isolation and Purification of Bovine κ-Casein Glycomacropeptide: A Review
Sialic acid is a carbohydrate moiety of κ-casein glycomacropeptide (GMP), which is a 64 amino acid residue
C-terminal sialylated phosphorylated glycopeptide released from κ-casein by the action of chymosin during cheese making.
GMP lacks aromatic amino acids including phenylalanine, tyrosine, and tryptophan. Because of its unique amino acid
composition and various biological activities, GMP is thought to be a potential ingredient for dietetic foods (e.g., a food
for PKU patients) and pharmaceuticals. Thus, increased attention has been given to the development of techniques to purify
GMP. In this review, techniques of GMP purification described in patents and scientific research papers were introduced.
A sialic acid assay is the important method to track GMP isolation and purification processes, for which the
thiobarbituric acid reaction with 1-propanol as a chromophore extracting solvent is an inexpensive, practical and specific
technique. Sephacryl S-200 gel filtration chromatography, cellulose acetate electrophoresis, and sodium dodecyl sulfate
polyacrylamide gel electrophoresis are the major techniques to identify sialic acid specific to GMP. Sephacryl S-200
chromatography and cellulose acetate electrophoresis are also used to detect GMP sialic acid in whey pearmeate and whey
added commercial margarine samples. Future research includes development of an economical industrial scale method to
produce high purity GMP.
Keywords: Bovine milk, caseinomacropeptide, cheese whey, sialic acid, sweet whey, thiobarbituric acid reaction, κ-casein
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