A COMPARISON OF THE VISCOELASTIC PROPERTIES OF CONVENTIONAL AND MAILLARD PROTEIN GELS

The properties of gels prepared by heating solutions of bovine serum albumin (BSA) for 30 min at 121C in the presence and absence of glucono-delta-lactone (GDL gels) and xylose (Maillard gels) were compared. During formation the pH of the Maillard and GDL gels decreased to 4.9 whereas the pH of the gels formed in the absence of GDL or xylose remained near neutral. Maillard gels show much less syneresis compared with the GDL gels and contained nondisulphide covalent crosslinks as evidenced by very low protein solubilities in mixtures of sodium dodecyl sulphate and beta-mercaptoethanol. Both the GDL and Maillard gels could be formed at much lower protein concentrations than the neutral conventional gels. The stress relaxation of the gels in compression was measured and the response analyzed using Peleg's equation. The parameters in this equation were not strongly dependent on protein concentration or degree of deformation. The neutral pH gels were far more elastic than the low pH gels, but despite the difference in crosslinking mechanisms the viscoelastic behaviour of the Maillard and GDL gels was similar. However, the break strength and asymptotic residual modulus of the Maillard gels were higher. It is suggested that the stress relaxation occurs in weaker, noncovalently linked regions of the gel, whereas the nondisulphide covalent crosslinks in the Maillard gels reinforce strong regions already containing disulphide linkages.