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Highlights in Chemical Science

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A good egg


27 May 2009

UK and Dutch scientists have mimicked an ancient Chinese culinary technique of preserving eggs to study how proteins cause disease.
 
Erika Eiser from the University of Cambridge and colleagues looked at how proteins in egg whites altered during this preservation process. The Chinese method involves wrapping raw eggs in an alkaline paste of lime, clay, salt, ash and tea and storing these so-called century eggs for several months. Eiser modified the method by incubating a boiled egg in a strong alkaline sodium hydroxide-salt solution for up to 26 days. 

 

egg

Hard boiled egg whites become a transparent gel in an alkaline solution
   

 

After peeling back the shell, Eiser found that the egg white had transformed into a gel. This transformation is caused by changes in the way protein strands, called ovalbumin, in the white are held together. Boiling an egg causes bonds between the protein strands to break and the proteins to partially unfold. The proteins then come together, or aggregate, in a different way to form the opaque and brittle white. The transformation was thought to be irreversible, but the alkali causes the proteins in the white to aggregate into fine strands to form a transparent and elastic gel. Eiser found that the gel was more stable than the white, and could be heated without changing its structure.   

Paul Bartlett, an expert in colloids and protein aggregation at the University of Bristol, UK, comments that Eiser's findings 'will be important for understanding protein gels and will inspire more work in colloidal materials.'   

'Similar chemical transformations could be used to change the properties of protein aggregates not only in food but also in other biomaterials,' says Eiser, who plans to test the method on different proteins. 'If we understand the mechanism that drives aggregation then we could slow it down or reverse the aggregation into something else.' This could be important in preventing diseases caused by unnatural protein aggregation such as Alzheimer's. 

Anna Roffey 

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Link to journal article

Molecular cooking: physical transformations in Chinese century eggs
Erika Eiser, Caroline S. Miles, Nienke Geerts, Peter Verschuren and Cait E. MacPhee, Soft Matter, 2009, 5, 2725
DOI: 10.1039/b902575h

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