Would you prefer your eggs sunny side up or easy over? Scrambled, maybe? However, there is something to say for a nice century egg, a pidan, and its hearty flavour, cheese aroma, its translucent and tea-colored “white” and bold green yolk. This Asian delicacy is prepared following a time consuming process. Duck eggs are wrapped in ash, salt, quicklime (a mixture of calcium carbonate and oxide) and, sometimes, tea and left to rest for a hundred days Lead oxide can be added to speed up the maceration; the gourmet minding his mental health and hand-eye coordination can substitute it for zinc oxide. The resulting product can be preserved for weeks, the ‘century’ of its name being a slight hyperbole of its resilience.
Since 1916, chemists attempted to understand the science behind the transformation. They found that the alkalinity of the solution is the main agent of transformation along with divalent cations, helped by the occasional Bacillus cereus and macerans, the eggs emerge in their famed appearance. From 9, the pH of the white can climbs to as high as 13 and the pH of the yolk, from 6.5 to 9. Apart from proteolysis, dehydration of the white and degradation of the yolk’s lecithin, such pH jumps also allows for racemisation of amino acids and an intricate unfolding process of the ovalbumin : egg white’s most abundant protein.
Pidan attracted the attention of gel specialists. Researchers at Cambridge observed that the ovalbumin aggregates in a particular way under the action of alkali. Most of the research on proteins colloids has focused on amyloids fibrils: denatured proteins, which, regardless of their sequence, assemble in long b-strands (Alzheimer’s disease is a famous example). The firmness of the century eggs comes be from more obscure structure. Under the slow action of extreme pH, the ovalbumin unfolds only partly. The denatured strands of proteins coagulate, forming fine chains between still-folded cores. The later are strongly ionized and kept away from one another by electrostatic repulsion. The resulting structure creates an intricate pattern of fine strands and ordered cores that are resistant even to boiling water. The pattern is uncommon in nature, but some believe it could shed light on the assembly of protein folds, opening the door on new horizons of biochemistry. As of what the traditions of the East can inspire even Cambridge’s biophysicists...
Since 1916, chemists attempted to understand the science behind the transformation. They found that the alkalinity of the solution is the main agent of transformation along with divalent cations, helped by the occasional Bacillus cereus and macerans, the eggs emerge in their famed appearance. From 9, the pH of the white can climbs to as high as 13 and the pH of the yolk, from 6.5 to 9. Apart from proteolysis, dehydration of the white and degradation of the yolk’s lecithin, such pH jumps also allows for racemisation of amino acids and an intricate unfolding process of the ovalbumin : egg white’s most abundant protein.Pidan attracted the attention of gel specialists. Researchers at Cambridge observed that the ovalbumin aggregates in a particular way under the action of alkali. Most of the research on proteins colloids has focused on amyloids fibrils: denatured proteins, which, regardless of their sequence, assemble in long b-strands (Alzheimer’s disease is a famous example). The firmness of the century eggs comes be from more obscure structure. Under the slow action of extreme pH, the ovalbumin unfolds only partly. The denatured strands of proteins coagulate, forming fine chains between still-folded cores. The later are strongly ionized and kept away from one another by electrostatic repulsion. The resulting structure creates an intricate pattern of fine strands and ordered cores that are resistant even to boiling water. The pattern is uncommon in nature, but some believe it could shed light on the assembly of protein folds, opening the door on new horizons of biochemistry. As of what the traditions of the East can inspire even Cambridge’s biophysicists...
Further reading
Blunt K. et al., J. Biol. Chem (1916), 28, 125-34
Wang J. et al., Crit. Rev. Microbiol. (1996), 22, 101–38
Eiser E. et al., Soft Matter, (2009), ), 5, 2725-30
Blunt K. et al., J. Biol. Chem (1916), 28, 125-34
Wang J. et al., Crit. Rev. Microbiol. (1996), 22, 101–38
Eiser E. et al., Soft Matter, (2009), ), 5, 2725-30
