Modification of lysozyme by dry-heating: small cause, big effect

Egg white dry-heating is usually achieved in industry to improve gelling and foaming properties. Major modifications of protein structure have been put forward to explain such functionality improvement. But as for lysozyme, one of the egg white proteins, dry-heating results in a great increase of foaming properties, without any significant modifications of structure, as determined thanks to usual analytical methods for secondary and tertiary structure determination. On the other hand, chemical modifications of the protein sequence could be highlighted for about 40% of lysozyme molecules: up to 5 Asp/Asn residues were changed for succinimide residues after dry-heating for 7 days at 80°C. These modifications result in more tensioactive forms, compared to native lysozyme. However, these "succinimide lysozymes" do not explain all the interfacial properties of dry-heated lysozyme. Indeed, the whole dry-heated lysozyme, that contains other modified forms supposed to be isoaspartate residues, do not have exactly the same behaviour. Finally, it can be concluded that lysozyme dry-heating induces several kind of modifications. And some of these modifications are different from structure changes usually mentioned to explain modification of protein properties. Anyway, dry-heated lysozyme is actually a very efficient foaming agent, contrary to the native one