Glycation of heat treated B-lactoglobulin: effects on foaming properties

Abstract

In this paper, the effect of glucose-glycation of beta-lactoglobulin (monomer 88%, dimer 12%) on foaming properties has been studied in 20 mM phosphate buffer at pH 6.8. The results obtained by electrophoresis, circular dichroism and fluorescence quenching showed the presence of small amounts of aggregates of higher molecular weight, while only slight changes in the tertiary structure flexibility of the glycated protein were detected. The improvement on foaming properties (foamability and foam stability) after glycation was promoted by heat treatment in the dry state (96 h at 50 °C) rather than by sugar conjugation. On the other hand, treated beta-lactoglobulin was obtained by heating a protein solution (55 mg mL-1 in 20 mM phosphate buffer at pH 6.8) at 85 °C for 3 min. This heated protein sample (monomer 51%, dimer 27%, trimer 19%) formed foams with good stability. After glycation, spectroscopic measurements demonstrated that no significant changes were introduced in protein conformation, since the substrate used were composed by unfolded species. However, the additional presence of oligomers of the protein founded after sugar conjugation, decreased the volume foam stability, probably due to steric impediment that diminished the viscoelastic stiffness of the interfacial film. The variation of volume foam stability caused by the different treatments assayed in this work, resulted from the action of these treatments on disproportionation rather than on liquid drainage from the foam