Electrochemical studies of the interfacial behaviour of alpha-lactalbumin and bovine serum albumin

Knowledge of the conformational behaviour of proteins as a function of temperature is important in the thermal processing of foods. Equally important is their interfacial behaviour with surfaces under these same processing conditions. This paper describes electrochemical techniques developed to study these structurally related properties of proteins. The interfacial behaviour of alpha-lactalbumin and bovine serum albumin was studied on a platinum electrode using cyclic voltammetry over a temperature range from 273 to 363 K. It was found that both proteins adsorbed strongly on the metal surface. As the temperature was increased up to the denaturation temperature of the protein, the surface charge density for protein adsorption also increased due to the conformational unfolding. Above the temperature for denaturation, the surface charge density continued to increase. Mixtures of the two proteins resulted in a substantial increase in surface charge density above the denaturation temperatures. A comparison of surface concentrations (Gamma) of cyclic voltammetric measurements with those for ellipsometric measurements reported in the literature showed a similar behaviour with increasing adsorption with temperature. A value of 17 +/- 4 carboxylate groups for the alpha-lactalbumin protein was determined from an analysis of the surface coverage which is consistent with the number of acidic residues on the protein. (C) 1997 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology.