Have you ever wondered what goes into making an egg? Or how an egg can be considered a “food production”? In this blog post, we will take a closer look at the structure of an egg and learn about the different parts that make it up.
There are many varieties of eggs found around the world, but only a few are used for human consumptions for various reasons. The eggs can be of fish, poultry, game birds or even reptiles, but in cooking we refer to eggs, we are always talking about poultry and eggs of birds that are reared for consumption of meat.
So let’s dive into the world of an Eggs.
The different parts of an egg or Structure of Eggs
The egg is composed of shell, white and yolk. The egg white forms 2/3rd of the whole egg and the yolk forms 1/3rd.
Shell
It is the outer covering of the egg and is composed of Calcium Carbonate. It may be white or brown depending upon the breed of the chicken.
Shell gives shape to the egg and holds the inner contents. It contains thousands of pores that allow CO2 and moisture to escape, as well as air to enter. The shell is covered by a cuticle membrane or Bloom and should not be washed. The bloom acts as protective covering blocking the pores, and prevents moisture loss and bacterial contamination. When eggs are washed before going to the market, the cuticle is removed. To protect the egg, the washed eggs are coated with a thin film of edible oil.
Yolk
Egg yolk is the yellow part of an egg that contains most of the egg’s nutrients. It is rich in protein, fat, vitamins, and minerals. Egg yolks are also a good source of choline, a nutrient that is important for brain development.
The yolk is separated from the white by a membrane called vitelline membrane. This membrane prevents the mix of both yolk and white. 1/6th parts of the egg yolk contains proteins, 1/3rd fat and the rest water, Vitamins and minerals like Calcium, Phosphorus, Iron etc.
Vitelline
It is a clear seal that hold the egg yolks.
Chalazae
These are the twisted cord-like strands of the egg white. They anchor the yolk in the centre of the egg. Prominent chalazae indicate high quality.
Shell Membranes
Two shell Membranes, inner and outer membrane, surround the albumen. They form a protective barrier against bacteria. Air cell forms between these membranes.
Air Cell
It is the pocket of air formed at the large end of the egg. This is coused by the concentration of the contents on cooling after the egg is laid. The air cell increases with the age of the egg as there is considerable amount of moisture loss.
Thin Albumen
It is nearest to the shell. When the egg is broken there will be a clear demarcation of the thin and thick albumen. As the egg gets older, these two albumens tend to mix into one another.
Thick Albumen
It stands high and spreads less than the thin white in a high quality egg. It is an excellent source of riboflavin and protein.
Composition of an Egg
| Parts | Number | Weight | Water | Protein | Fat |
| Whole Egg | 1 | 50 Gms | 74% | 13% | 12% |
| Egg white | 1 | 33 Gms | 88% | 11% | Traces |
| Egg Yolk | 1 | 17 Gms | 51% | 16% | 31% |
Uses of eggs in food production or in Kitchen
Eggs play a crucial role in food production and are used in various ways across the industry. Here are some key uses of eggs in kitchen.
Food Manufacturing
Eggs are used as ingredients in a wide range of food products, including baked goods (cakes, cookies, pastries), pasta, noodles, sauces, dressings, mayonnaise, ice cream, custards, puddings, soups, and ready-to-eat meals. Eggs provide structure, texture, moisture, and flavor to these products.
Binding Agent
Eggs act as a binding agent in food production, helping to hold ingredients together. They are used in the production of meat products like sausages, meatballs, and burgers to bind the meat and other ingredients, creating a cohesive mixture.
Coagulation
Egg coagulate at 65 Degree Celsius and continue to thicken till 70 Degree Celsius.
Uses of eggs based upon coagulation are given below
- The process of coagulation thickens custard and sauce.
- Coagulated egg protein helps support cream puffs, cakes and breads. It binds together foods as in meat loaves and burgers. It also coats foods in form of eggs based batters.
- To clarify a consomme a chef beats in egg white into the soup.
Emulsification
The emulsifying properties of eggs are utilized in food production to create stable emulsions. Egg yolks acts as an emulsifying agent, because it’s protein can wrap itself around tiny globules of oil.
Yolk also contains lecithin which is an emulsifying agent.
Uses of eggs based upon emulsification
- Oil is added to yolks to form a mayonnaise
- The emulsifying power of egg yolks also contributes to the crumbly quality of a rich cake.
Leavening Agent
In certain baked goods, eggs contribute to leavening. The effectiveness of the leavening depends on the amount of air trapped within the egg. Yolks when beaten transform into thick light yellow foam. A little acid in the form of cream of tartar or a squeeze of lemon juice helps stabilize the foam and the yolks as even a small trace of yolks will prevent the whites from rising properly.
Use of eggs based upon leavening
- Eggs are used for making baked goods such as sponges and cakes. Leavening of eggs gives these products a lighter texture that is desirable.
Moisture Retention
Eggs help retain moisture in baked goods, preventing them from becoming dry and stale. The proteins and fats in eggs contribute to the overall moisture content, resulting in products that stay fresh for longer periods.
Color and Appearance
Eggs contribute to the color and appearance of various food products. For example, egg yolks provide a yellow or golden hue to baked goods, pasta, and noodles. In addition, egg wash (a mixture of beaten eggs and water) is brushed on bread, pastries, and pies before baking to give them a glossy and golden-brown finish.
Coating and Crumb Adhesion
Eggs are commonly used as a coating or adhesive in the production of breaded and fried products. They act as a binder, allowing breadcrumbs or batter to adhere to the surface of foods like chicken, fish, or vegetables, resulting in a crispy outer layer when cooked.
Egg Substitutes
In some food production processes, egg substitutes are used to replace whole eggs or specific components like egg whites or yolks. These substitutes are often utilized to accommodate dietary restrictions or preferences, such as vegan or cholesterol-free options.
Food Safety
In certain food production practices, eggs are utilized for food safety purposes. Pasteurized eggs are used to reduce the risk of foodborne illnesses associated with raw or undercooked eggs in products like dressings, sauces, or desserts.
Nutrition Value of Eggs
Nutritional value of eggs, based on a large egg (approximately 50 grams) that has been hard-boiled:
Calories: 78
Protein: 6.3 grams
Fat: 5.3 grams
- Saturated fat: 1.6 grams
- Monounsaturated fat: 2.0 grams
- Polyunsaturated fat: 0.7 grams
Cholesterol: 186 milligrams
Carbohydrates: 0.6 grams
Sugars: 0.6 grams
Fiber: 0 grams
Sodium: 62 milligrams
Vitamins and minerals:
- Vitamin A: 75.7 micrograms
- Vitamin D: 44.2 IU
- Vitamin E: 0.5 milligrams
- Vitamin K: 0.3 micrograms
- Vitamin B1 (thiamin): 0.03 milligrams
- Vitamin B2 (riboflavin): 0.2 milligrams
- Vitamin B3 (niacin): 0.1 milligrams
- Vitamin B6: 0.1 milligrams
- Folate: 23.5 micrograms
- Vitamin B12: 0.6 micrograms
- Biotin: 6.0 micrograms
- Pantothenic acid: 0.7 milligrams
- Calcium: 25.6 milligrams
- Iron: 0.9 milligrams
- Phosphorus: 86.7 milligrams
- Potassium: 63.5 milligrams
- Zinc: 0.6 milligrams
- Selenium: 15.4 micrograms
Selection of Eggs
Colour
The Colour has no direct effect on the quality of the egg. It depends on the breed, the type of bird and the food consumed. However avoid any eggs with patches formed on the surface as they indicate deterioration of eggs.
Size and Weight
It again depends on the type of bird. An average hens egg weighs around 50 gms. The weight should be proportional to the size of the egg. If the size is big and the weight is less, the air cell is big, which indicates that the egg is old.
Egg white
It should not be watery but firm. Firm albumen is a sign of freshness.
Egg yolk
Its colour again depends on the type & feed of the bird. The pigment contained is different feeds are different. Birds that feed on green grass or yellow corn will have a dark yellow colour because of the Carotenoids present in the grass. However, avoid eggs which have blood spots (meat spots). The blood spot means, that the egg is fertilized and nearing hatching (the blood spots are caused by the rupture of a blood vessel, during egg formation).
Approximately 1% of all eggs will have these spots which are detected and removed during grading. Electronic blood detectors are sometimes used for grading. Although the blood spot may be objectionable to the consumer, the eggs are chemically and nutritionally fit to eat. In fact, the blood spot is an indicator that the egg is fresh. As the egg ages, the yolk removes water from the albumen and dilutes the blood spot.
Free from cracks
The egg must be free from cracks. If the egg is cracked, there are chances that the egg is spoilt, since the micro-organisms have an easy access into the egg.
Flavour and Odour
Generally the eggs don’t have any odour from the outside, except that of the packing material, which must not be strong smelling. Sometimes the smell may penetrate into the egg. Hence, eggs are usually stored away from strong flavoured foods like fish, onions, garlic etc.
In order to maintain the standard, size, quality, colour and weight, the distributors buy eggs, usually from on-farm only, where the diet is kept constant.
If the birds are of the same breed and feed, the standard can be maintained.
Storage of eggs
Care must be taken in handling and storage of the eggs. They should be stored in their packing trays with the blunt end upwards and the temperature of 7-13°C, at a relative humidity of 70-80%. This way, it can be kept for a month. It should be kept away from onions, garlic, fish etc. Frozen eggs are stored at -18°C. When defrosted, it should be used in the same day.
Reasons for storage of eggs:
- As soon as the eggs are laid, they start deteriorating as they come in contact with the atmosphere.
- The dense albumen becomes thin and watery.
- Water from the white passes through the yolk; thus lowering its solids as the vitelline membrane is weakened. Chalaza starts to disintegrate and no longer holds the yolk in the centre.
- If exposed to air, the moisture evaporates and the air cell increases in size.
- The egg may absorb off-odours, shell being porous.
- Fresh yolk is slightly acidic, whereas white is alkaline. Loss of carbon dioxide from the egg results in deterioration.
Cooking of Eggs
The most important rule of egg cookery is avoid high temperature and long cooking time. In other words, don’t overcook eggs. Overcooking produces tough eggs, discolouration and it flavour too. Egg white coagulates at 60-65°C, yolk at 65-70°C, whole beaten egg at 69°C and custard at 79-85°C, depending on the amount of milk used. White coagulates before yolk and hence it is possible to boil eggs with firm white and soft yolk. Coagulation depends on length of heating and the presence of added materials like vinegar and salt, which will speed up the coagulation.
Conclusion
In conclusion, eggs are a versatile and nutritious food that can be used in a variety of ways in food production. They are a good source of protein, vitamins, and minerals, and they can be used in both savory and sweet dishes. Eggs are also a sustainable food source, as they require relatively few resources to produce.
I hope this blog post has given you a better understanding of the structure, composition, uses, and nutrition value of eggs. If you have any questions, please feel free to leave a comment below.