Glycomacropeptide (GMP) is a C-terminal part (f 106–169) of kappa-casein which is released in whey during cheese making by the action of chymosin. GMP being a biologically active component has gained much attention in the past decade. It also has unique chemical and functional properties. Many of the biological properties have been ascribed to the carbohydrate moieties attached to the peptide. The unique set of amino acids in GMP makes it a sought-after ingredient with nutraceutical properties. Besides its biological activity, GMP has several interesting techno-functional properties such as wide pH range solubility, emulsifying properties as well as foaming abilities which are shown to be promising for applications in food and nutrition industry. These properties of GMP have given new dimension for the profitable utilization of cheese whey to the dairy industry. A number of protocols for isolation of GMP from cheese whey have been reported. Moreover, its role in detection of sweet/rennet whey adulteration in milk and milk products has also attracted attention of various researchers, and many GMP-specific analytical methods have been proposed. This review discusses the chemico-functional properties of GMP and its role in the detection methods for checking cheese or sweet whey adulteration in milk. Recent concepts used in the isolation of GMP from cheese whey have also been discussed.

Sialic acid, being a biologically active compound, is recognised as an important component of milk and milk products. Almost all the sialic acid estimation protocols in milk require prior hydrolysis step to release the bound sialic acid followed by its estimation. The objective of this work was to estimate sialic acid in milk and milk products by fluorimetric assay which does not require a prior hydrolysis step thus decreasing the estimation time. The recovery of added sialic acid in milk was 91·6 to 95·8%. Sialic acid in milk was found to be dependent on cattle breed and was in the range of 1·68-3·93 g/kg (dry matter basis). The assay was further extended to detect adulteration of milk with sweet whey which is based on the detection of glycomacropeptide (GMP) bound sialic acid in adulterated milk. GMP is the C-terminal part of κ-casein which is released into the whey during cheese making. For detection of adulteration, selective precipitation of GMP was done using trichloroacetic acid (TCA). TCA concentration in milk was first raised to 5% to precipitate milk proteins, especially κ-casein, followed by raising the TCA concentration to 14% to precipitate out GMP. In the precipitates GMP bound sialic acid was estimated using fluorimetric method and the fluorescence intensity was found to be directly proportional to the level of sweet whey in adulterated milk samples. The method was found to detect the presence of 5% sweet whey in milk.