dioxide that has not yet leaked out through the shell. The older the egg, the more transparent the egg white.
The amount of fat and cholesterol and the composition of the fat are influenced by diet.
Alkaline pH value Egg white is one of the few alkaline food products that exist. In a freshly laid egg the pH value is approx. 7.6, but it increases during the first 1-2 days to 8.6 and then to 9.7. The rate at which the pH value increases depends on the storage conditions. The higher the temperature, the faster the increase in pH value.
The chalazae The yolk is held in place by two screwshaped strands of egg white – the chalazae, which are formed from egg white proteins. The chalazae are most visible in fresh eggs and can be hard to spot in a boiled egg.
The yolk The yolk is a single cell that represents about 28 % of the weight of the egg. The nucleus, called the embryonic disk, can be seen as a small white spot on the outside of the yolk when the egg is opened. The yolk is surrounded by a protective membrane, the vitelline membrane, which becomes weaker the older the egg is. The yolk has much lower water content than the egg white, just under 50 %. About 2/3 of its dry matter is fat and 1/3 is protein. The fat content consists primarily of triglycerides, cholesterol, and the phospholipid lecithin.
8 | Egg structure
Colour of the yolk The diet determines the colour of egg yolk. If the hen is mainly fed yellow and orange-pigmented food, this is the colour that is more prominent in the egg yolk. A relatively colourless feed gives almost colourless yolks. In these cases, the manufacturer often adds a small amount of plant supplements that provide the yolk with the colour that consumers like best – namely golden or lemon-coloured.