The main objective of this work, was the isolation, chemical and nutritional (in vitro) characterization of the two main protein fractions of bovine blood serum. Immediatly after hygienic collection at the slaughter house the blood was coagulated and the cellular fraction separated by centrifugation under appropriate conditions. The globulin (GB) fraction was precipitated from blood serum by 50% saturation with ammonium sulfate. The supernalant was separated by centrifugation and the (NH4)2SO4 saturation elevated to 80%. Under this condition BSA precipitated. Precipitation (recovery) of proteins amounted to 98% of total serum protein, in the two fractions. Both GB and BSA were characterized as to proximate percent composition, mineral, amino acid profiles, essential amino acid score (EAE), protein digestibility, and protein digestibility corrected amino acid scoring (PDCAAS). Protein concentration in both fractions was around 85%. BSA presented high concentrations of lysine, histidine and sulfur amino acids, particulary cistine. The EAE for BSA was 70%, tryptophan being the most limiting amino acid, and for GB the EAE score was 87.8% with isoleucine as the most limiting amino acid. PAGE-SDS and densitometry permitted the fractions characterization as the number of protein bands molecular weight and relative proportions among the various proteins.
serum proteins; albumin; globulin; fractionation; nutritive value
