Conformational changes and intrinsic viscosity of bovine serum albumin complexed with D-glucose

Abstract

Maillard complexes of bovine serum albumin and D-glucose were prepared by equilibrating a freeze-dried mixture of the protein and sugar at 501 relative humidity, followed by heating at 55°C for periods up to 40 hr. No visible brown pigmentation was observed in the resulting powders. However, 70% reduction in free amino groups was measured during the heating period. Improved solubility over bovine serum albumin concomitant with increases in molecular weight, net negative charges on the molecules and Stokes radii demonstrate the formation of soluble premelanoidins in complexes heated for up to 15 hr. Polymerization and insolubilization was observed by prolonged heating of the complexes. Intrinsic viscosity of the native complexes was not significantly different from that of bovine serum albumin molecule, indicating that the improved heat stability of the soluble complexes is due to the interference with protein interaction and isoelectric aggregation of the denatured protein molecule. Loss in nutritional value of Maillard reaction products is not a consequence of interference of attack of proteolytic enzymes on the peptide chain of the protein molecule.