Detection of sialylated phosphorylated kappa-casein glycomacropeptide electrophoresed on polyacrylamide gels and cellulose acetate strips by the thiobarbituric acid and malachite green dye reactions.

A 64 amino acid residue sialylated phosphorylated glycomacropeptide (GMP) from bovine sweet whey can be detected as a Coomassie blue-staining peptide by electrophoresis on sodium dodecyl sulfate (SDS)-polyacrylamide gels. There is, however, limited information available concerning detection of GMP as a sialylated phosphorylated compound. Samples of GMP were electrophoresed on SDS-polyacrylamide gels or cellulose acetate strips (CAS). Immediately following electrophoresis, fractions obtained by cutting gels or strips were subjected to sialic acid determination by the thiobarbituric acid reaction and phosphorus determination by the malachite green dye reaction. Both determinations were found to be sensitive enough to detect approximately 20 and 40 microg of GMP in CAS and SDS gels, respectively. Further studies demonstrated that sialylated phosphorylated GMP can be detected on either SDS gels or CAS loaded with whey products or whey-added margarine residues.

Use of epichlorohydrin-treated chitosan resin as an adsorbent to isolate kappa-casein glycomacropeptide from sweet whey.

This study was undertaken to develop a method to isolate glycomacropeptide (GMP), a bioactive compound, from sweet whey by using chitosan resins as anion exchangers. Shrimp shells were used to prepare two chitosan (polyglucosamine) resins, one with the primary amine (-NH(2)) (resin A) and the other with the secondary amine (-NH-) (resin B) as the major functional group. These resins were tested as adsorbents for the isolation of GMP from sweet whey, and the results obtained were compared with those obtained with commercial anion exchangers. The most important finding in this experiment was that the GMP binding capacity of resin A was much higher than that of resin B. Resin A may be the anion exchanger to be tested for industrial scale production of GMP. Amino acid analysis of the GMP-depleted whey fraction suggests that this product can replace sweet whey as an ingredient in various food products including infant formulas, bakery products, and beverages.

Purification of kappa-casien glycomacropeptide from sweet whey with undetectable level of phenylalanine.

Glycomacropeptide (GMP) found in sweet whey is a biologically active compound released from kappa-casein by the action of chymosin during cheese making. This study was undertaken to purify GMP from sweet whey as a research chemical on a laboratory scale. Glycomacropeptide was isolated from proteins and other non-GMP compounds by deproteinization with trichloroacetic acid and gel chromatography on Sephacryl S-200. The purified GMP accounted for 0.12% of dry sweet whey powder and contained 107.0, 50.9, 61.2 and 4.3 microg, respectively, of sialic acid, galactose, galactosamine and phosphorus per mg dry weight. The GMP was of high purity, with its amino acid composition showing undetectable levels of phenylalanine, tyrosine and arginine, the amino acids that do not occur in bovine GMP. On gel electrophoresis, the GMP showed a single broad band with an average mobility faster than that of carbonic anhydrase (molecular weight = 31 kDa). The purified GMP may be used as a standard glycopeptide in chromatography and electrophoresis and may also be used to test various known or unknown properties and biological activities of this compound.