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Lesson Note

Subject: Food And Nutrition

Topic: Food Study
Sub Topic: Eggs

Lesson Objectives: By the end of the lesson, the learners should be able to:

  1. Describe the structure of an egg;
  2. State the nutritive value of eggs;
  3. State the factors to be considered when choosing eggs;
  4. Describe various ways eggs can be prepared;
  5. Mention the uses of eggs in cookery

Lesson Summary Aids: see reference materials below contents.

Lesson Summary / Discussion

Eggs

Eggs are are organic vessels produced or laid by female animals of many different species mainly for consumption or hatching. Examples of these animals are birds, reptiles, amphibians, a few mammals, and fish, and many of these have been eaten by humans for thousands of years. Bird and reptile eggs consist of a protective eggshell, albumen (egg white), and vitellus (egg yolk), contained within various thin membranes. The most commonly consumed eggs are chicken eggs. Other poultry eggs including those of duck and quail also are eaten. Fish eggs are called roe and caviar.

Eggs generally have a common structure and can be produced by chicken duck turkey and goose.

Chart Structure Of  An Egg (A Typical Hen Egg)


Eggs are spherical in shape with one end pointed and the other end blunt. they are covered by a hard protective shell which can either be white or brown in colour. the colour of the shell depends upon the breed of the chicken and it is unrelated to the colour of the yolk or to the food value and quality of the egg. the shell is porous and this allows for moisture and gaseous exchange with the surrounding air. The porosity of the eggshell allows for the development of the embryo but it decreases the keeping quality of the egg. Immediately beneath the eggshell are two inner membranes which separates at the blunt end of the egg farming what is known as the airspace. at the centre of the egg is the egg yolk which is held in position by two cord like structures called chalazae. The egg yolk is covered by a membrane known as vitellin membrane. Immediately after the vitellin membrane is the thick egg white. a high proportion of The tick egg white is an indication of good quality of the egg.

Nutritive value of An Egg

The diet of laying hens also may affect the nutritional quality of eggs. For instance, chicken eggs that are especially high in omega-3 fatty acids are produced by feeding hens a diet containing polyunsaturated fats from sources such as fish oil, chia seeds, or flaxseeds. Pasture-raised free-range hens, which forage for their own food, also produce eggs that are relatively enriched in omega-3 fatty acids when compared to those of cage-raised chickens. A 2010 USDA study determined there were no significant differences of macronutrients in various chicken eggs.

About 3/4 of the egg weight is water. this is followed by protein fat and minerals elements in decreasing order. Although proportion varies among eggs, the white is usually about 58% of the weight of the whole egg, the yolk is 31% and the shell is 11%. The the yolk is a more concentrated food than the white since it contains only about 51% water while egg whites contains over 87% water. The yolk also contains more protein fats minerals and vitamins than the white which is totally devoid of fat.
the protein of egg as a whole is of good biological value and is easily digested. Eggs can therefore be used to replace meat, poultry or fish in the diet.
Eggs also contains vitamins A and d and the b complex vitamins. Both egg yolk and white are good sources of riboflavin and it is this vitamin that is responsible for the slightly greenish tint to an egg white. Eggs are also rich in minerals such as iron sulphur phosphorus and calcium. They are however deficient in carbohydrates and ascorbic acid.

Factors To Consider When Choosing Eggs

It is very important to make sure that stale eggs are not purchased. This means that the egg must possess the following qualities:
  1. When held against a source of light it should be bright and not opaque.
  2. An opaque egg is not good and should not be purchased. This process is known as scandling.
  3. When broken, the egg yolk should be intact and surrounded by the egg white.
  4. A diffused York (one in which yolk and egg white are mixed together) is bad and should not be purchased. When immersed in salted water it should sink and not float.
  5. When broken there should be no offensive odour produced.
  6. Egg with good quality does not produce sound when shaken.

Preparation Of Eggs

A. Boiled Egg: this method of preparing egg is very common. it involves immersing the egg completely in water and bringing the water to the boil for about 3 to 5 minutes. The egg can either be soft boiled or hard boiled. in a soft-boiled egg a protein undergoes partial coagulation while in a hard-boiled egg complete coagulation of the protein takes place. the surface of the yolk of a hard-boiled egg sometimes a dark green. This colour result from the ferrous sulfide formed by a combination of the ions of the yoke and the sulphur of either the white or yolk. the greenish colour is more likely to occur when eggs have been overcooked or allowed to cool slowly. A greenish colour is more likely to form with eggs that have been stored for a long time than with fresh eggs.
Eggs (boiled) supply several vitamins and minerals as significant amounts of the Daily Value (DV), including vitamin A (19 percent DV), riboflavin (42 percent DV), pantothenic acid (28 percent DV), vitamin B12 (46 percent DV), choline (60 percent DV), phosphorus (25 percent DV), zinc (11 percent DV) and vitamin D (15 percent DV). Cooking methods affect the nutritional values of eggs.
B. Fried Egg: in this method of egg preparation, a thin layer of oil or fat is put into the frying pan. the fat should be allowed to hit to a point at which it will sizzle on addition of a drop of water. The egg should be broken and emptied into the hot oil. The egg is done cooked all until the white is set. It is advisable to stire the egg while on the fire to avoid burnt.
C. Scrambled egg: this method of egg preparation, fat or oil is put in the frying pan and is allowed to heat up. The eggs are then broken into a cup. Salt, pepper, milk, tomato juice or any other fruit or seasoning can be added as desired. The mixture is then beaten with a fork to break up the yolk. The mixture is poured into the frying pan and cook over a low heat. it is Ted gently so that the thickened portions are lifted from the bottom of the pan and the uncooked portion allowed to run down. If the steering is vigorous and constants, tiny cord like egg particles will be obtained instead of a large soft mass. The cooking is discontinued when the mixture is coagulated and before it becomes dry.
D. Omelette: related used for omelette is similar to that of scrambled eggs. In this method, the frying pan containing the fat or oil which is about a teaspoon for each egg is heated over the fire to melt. The egg mixture which does not contain any liquid is added and the Palm placed over a moderate heat. As the omelette cooks and eggs coagulate, the omelette should be lifted from the edge towards the centre and the pan tipped so that the uncooked mixture flows under the cooked portion. When the home mixture becomes creamy and the bottom is slightly browned, the omelette is rolled or folded in half by lifting the handle of the pan and manipulating the omelette with the aid of a spatula. At this point, grated cheese, chopped meat of fish, as well as creamed vegetables can be put on the omelette before it is folded if desired.
E. Poached Eggs: in this form of egg preparation, enough water to cover the Earth completely is brought to the boil in a shallow pan, an egg is broken into a cup and it dropped gently into the water. After dropping all the eggs, the water is reheated to simmering, and is removed from the heat, covered and allowed to stand for about 3 to 5 minutes until the eggs are firm but not hard. Sort of vinegar is sometimes added to the water in which eggs are poached to Hasting coagulation and thus improve the shape of the poached eggs. Alternatively eggs can be poached in a specially designed pants for poaching.

Uses of Eggs In Cookery

  • Eggs serve as thickening agent in sauces and soups such as custard sauce.
  • They serve binding agent.
  • They serve coating agent before frying fillet of fish, or meat cakes.
  • Eggs serves as fine agent in mayonnaise and cake mixtures.
  • Egg also serve as garnishing in dishes.
  • Eggs serve as leavening or raising agent. This is as a result of the ability of eggs to enclose air when whisked. After heating, the enclosed expands and thereby raising the food mixture.
  • They serve as glazing agent. This happens when slightly beaten eggs are brushed over pastry and scones. This helps to give a golden brown gloss to the finished dish.
  • Generally eggs add to the nutritive value of dishes.

Done studying? See previous lessons in Food And Nutrition

Lesson Evaluation / Test

With the aid of a diagram describe the structure of an egg.
What are the factors to consider when choosing eggs?
Enumerate the various uses of eggs in cookery.
Discuss in detail the various methods of preparing eggs.
Teachers/Learners Contribution
1. Mention the animals that lay eggs. Share your knowledge on the comment section.
2. Are there other methods of preparing eggs you know? Share your knowledge on the comment section.

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Resources
Coorey R, Novinda A, Williams H, Jayasena V (2015). “Omega-3 fatty acid profile of eggs from laying hens fed diets supplemented with chia, fish oil, and flaxseed”. J Food Sci. 80 (1): S180–7. doi:10.1111/1750-3841.12735. PMID 25557903.

Kenneth F. Kiple, A Movable Feast: Ten Millennia of Food Globalization (2007), p. 22.

Image Credit: researchgate.net