Cross-linked ovalbumin catalyzed by polyphenol oxidase: Preparation, structure and potential allergenicity

Ovalbumin (OVA) is described as one of the major allergens in hen's egg, and it is the most abundant protein in egg white. Enzyme-mediated covalent cross-linking of food proteins, can influence their structure and allergenicity. The aim of this study was to investigate the potential of polyphenol oxidase from Agaricus bisporus to cross-link OVA (CL-OVA) in the presence or absence of caffeic acid, followed by characterizing the structure and allergenicity of CL-OVA. A single-factor experiment was designed to assess the optimum conditions for cross-linking of OVA by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Under the optimal conditions, structural changes in OVA were analyzed by circular dichroism, ultraviolet and fluorescence spectra. It was shown that CL-OVA became unordered and unfolded, and more tyrosine and tryptophan residues and hydrophobic groups were exposed onto the surface of molecules when compared to the native OVA. Enzyme-linked immunosorbent assay indicated that IgG and IgE binding abilities to OVA significantly reduced after cross-linking. All the findings demonstrated that enzymatic cross-linking in the presence of caffeic acid as a mediator may decrease the antigenicity and potential allergenicity, and the changes of the modified OVA were most likely a consequence of some changes or adjustment in the local conformation of OVA and the epitopes of OVA by cross-linking.