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Article Type

Original Study

Abstract

The polyacrylamide gel electrophoresis sodium dodecylsulfate (SDS-PAGE) has been extensively used to separate native and denaturalized proteins. In various countries this has been useful to detect milk adulteration with whey, which is a fraud according to the current legal standards. The presence of glycomacropeptide (GMP) constitutes a marker of adulteration. It is released to the serum due to the hydrolysis of --casein peptide catalyzed by rennin incheese elaboration. In this work, the GMP detection was standardized as a pasteurized milk adulteration index, by means of GMP isolation with sequential precipitation in trichloroacetic acid at 24% and 50%, treatment with ethanol-ether and resuspention in buffer Tris-HCl 0.05 M, EDTA 1 mM, from sweet whey, acid whey, recently drawn raw milk, mixtures of whey milk; pasteurized milk and powder milk locally commercialized. Precipitates were analyzed by SDS-PAGE and GMP was evidenced as a trimer of 20.8 kDa in samples of sweet whey, and mixtures of whey: milk (1, 5, 10 and 50%), but absent in samples of acid whey and drawn raw milk.. The results obtained demonstrate that investigation of GMP by SDS-PAGE in milk, constitute a sensible and specific parameter to detect milk adulteration with whey, to levels as low as 1%, something that can not be revealed only with the evaluation of the physical-chemical parameters of milk.

Keywords

Casein, GMP, Milk adulteration, SDS-PAGE, Whey

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