STRUCTURE OF THE EGG
Eggs are produced by domesticated bird such as chicken, turkey, duck, goose and guinea fowl. The hen’s egg of average size weights approximately 56 g, they are covered with a hard protective shell which can be either be white or brown in colour. The colour of the bird depends upon the breed of the chicken and it is unrelated to the food value and quality of the egg. Eggs are spherical in shape with one end pointed and the other blunt.
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Immediately beneath the egg shell are two inner membranes which separate at the blunt end of the egg forming what is known as air space. At the centre of the egg is the egg yolk which is held in position by two cords-like structures called Chalazae. The egg-yolk is covered by a membrane known as Vitaline membrane. Immediately after the vitaline membrane is the thick egg white. A high proportion of thick white. A high proportion of thick white is an indication of good quality of the egg.
NUTRITIVE VALUE OF AN EGG
- Protein: the protein of eggs as a whole is of good biological value and is easily digested. Eggs can therefore be used to replace meat, fish and poultry in a diet.
- Vitamins: eggs also contain some vitamins such as Vitamins A, D and B-Complex. Both egg yolk and white are good source of riboflavin and is this vitamin that is responsible for the slightly greenish tint to an egg white.
- Mineral Salts: eggs are rich in mineral salts like iron, sulphur, phosphorus and calcium.
- Water: 51 percent of the yolk of egg contains water and the white contains 87 percent. This shows that egg contains a reasonable amount of water.
- Fat: the yolk of an egg contains appreciable amount of fat than the fat which is totally devoid of fat.
Note: eggs do not contain carbohydrate or starch; they should be combined with carbohydrate foods in order to give the necessary bulk.
FACTORS TO CONSIDER WHEN CHOOSING EGGS AND TEST FOR FRESHNESS
- When held against the source of light, it should be bright and not opaque.
- When broken, the yolk should be intact and surrounded by the egg white. A diffused yoke i.e. one in which yoke and egg white are mixed together is bad.
- When immersed in salt water, it should sink and float.
- When broken, there should be no offensive odour produced.
- When shaken, no sound should be produced if the egg is of good quality.
USES OF EGGS IN COOKERY
- Eggs are used to increase food value and to improve the flavours of food to which eggs are added. E.g. doughnut, pan cakes e.t.c.
- As a binding medium e.g. fish, cakes, yam balls.
- For coating foods for frying, e.g. fish, yam balls e.t.c.
- As thickening agents e.g. in sauce, custard e.t.c.
- As a raising agent in cake making.
- For garnishing, hard boiled eggs are sliced or wedged and used for garnishing salads.
- For glazing pastry, bread dough, biscuits e.t.c. before baking.
- Eggs are valuable in diet especially in that of growing children and invalids because they are rich in nourishment and easily digested.
- State 5 indications of egg freshness.
- Describe the structure of a typical egg.
Draw and label the structure of an egg.