Effects of Ionic Substances on the Adsorption of Egg White Proteins to a Stainless Steel Surface

Abstract

The surface fouling of food processing equipment by proteins was studied by investigating the adsorption of egg white proteins to the surface of stainless steel (SS) at pH 7.4 and 30 °C, and particularly the effects of different types of ionic substances. Ovalbumin and ovomucoid, acidic egg white proteins, were less adsorbed in the presence of phosphate (P_i), a multivalent anion, than in the presence of HEPES, an amphoteric ion. On the other hand, lysozyme, a basic egg white protein, was more adsorbed in the presence of P_i than in the presence of HEPES. Citrate as another multivalent anion and taurine as another amphoteric ion affected the respective adsorption of those egg white proteins similarly to P_i and HEPES. The adsorption of an egg white protein to an SS surface therefore depended on the combination of the type of protein and the effective charge of the coexisting ionic substance. This behaviour can be well explained by assuming that a small ionic substance precedes a protein in attaching to an SS surface, resulting in an alteration to the effective surface charge. Pretreating SS with a P_i buffer lowered the amount of ovalbumin adsorbed with the HEPES buffer, demonstrating that P_i can attach to and remain on the SS surface to affect the subsequent protein adsorption.