The eggs were produced by duck farmers in neighbouring Hebei province who are suspected of adding the dye to the animals' feed to give the yolks a more intense red colour.

Chinese consumers pay more for eggs with red yolks as they believe the red colour is a sign of quality and better nutrition. Some people think that the eggs become red from the shrimp in ducks' diets.

However Hou Shuisheng, a researcher from the Chinese Academy of Agricultural Science, told AP-foodtechnology that for ordinary eggs, “the colour of the yolk should be light yellow. Both bright yellow and bright red yolks are not natural, so it is certain that some dyes have been added”.

While government food safety officials told local media that the amounts of dye found in the eggs (as much as 0.137mg per kg of eggs) would not be dangerous unless consumed in great quantities, the news could heighten a growing lack of faith in the country's food safety standards.

Source: Food Navigator-USA