Scientists now have the solution to a long-standing egg riddle — and it could lower your chances of food poisoning.
- Shells contains nanostructured minerals associated with the protein osteopontin, also found in bone
- The structure of the egg changes as the embryo develops
- Finding could help breed chickens for stronger eggs, preventing salmonella contamination
Researchers from Canada's McGill University have cracked the mystery of how avian (and formerly dinosaur) eggshells are simultaneously strong enough to resist fracture from the outside yet weak enough for chicks to break from the inside.
It has to do with minute changes in the shell's nanostructure that occur during egg incubation.
Domestic chicken egg shells are about 95 per cent calcium-carbonate but the remaining 5 per cent includes a protein called osteopontin, according to the study published in Science Advances.
The protein was originally discovered in bone.
Dimitra Athanasiadou, a graduate student and lead author on the new study, found that a nanostructured mineral associated with osteopontin helps determine shell strength.
Changes in the nanostructure both help the chick grow and allow it to escape the shell later on.
During incubation the inside of the shell dissolves to give the developing embryo the calcium it needs to form its skeleton.
At the same time, the process weakens the shell just enough for the chick to break through when it hatches.
Discovery paves way for stronger eggs
The new understanding could lead to changes in the egg industry.
Professor Marc McKee, who led the study, said all the same nutritious things in eggs that help chick embryos to grow also make for a "very fertile growth field for pathogens".
"Most of all of us know about salmonella bacteria, which can cause food poisoning. It's a major problem in the egg industry where cracked eggshells or broken eggs will allow entry into the egg and cause food poisoning," he said
About 10-20 per cent of chicken eggs break or crack, he said.
"Once we know how to analyse nanostructure in eggs and what it means in terms of function … and how they contribute to hardness, then the egg industry for example can use that information to genetically select for strains of chickens that consistently produce stronger eggs."
The fragility of eggshells meant that new techniques and new equipment had to be used to prepare samples for study.
"Eggshells are notoriously difficult to study by traditional means, because they easily break when we try to make a thin slice for imaging by electron microscopy," Professor McKee said.