Resumen

GALINDO-AMAYA, Luz Mila; VALBUENA-COLMENARES, Emiro  y  ROJAS-VILLARROEL, Evelin. Standardization Of Glycomacropeptide Detection with SDS-PAGE as a Milk Adulteration Index. Rev. Cient. (Maracaibo) [online]. 2006, vol.16, n.3, pp.208-314. ISSN 0798-2259.

The poliacrylamide gel electrophoresis sodium dodecylsulfate (PAGE-SDS) 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 glicomacropeptide (GMP) constitutes a marker of adulteration. It is released to the serum due to the hydrolysis of k-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, pH 7.2 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. Analysis of fifteen samples of pasteurized milk (brands A, B, C, D and E) revealed the presence of GMP in ten of them, corresponding to brands A, B, C and E. Nevertheless after analyzing five samples of powder milk (brands F, G, H, I y K) this peptide was not observed. 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.

Palabras clave : Milk adulteration; whey; GMP; SDS-PAGE.