STRUCTURE OF AN EGG

Egg is primarily made up of shell, membranes, air cell, albumen, chalazae, vitelline membrane and yolk.

STRUCTURE OF AN EGG

Shell
Bumpy and grainy in texture, an eggshell is covered with as many as 17,000 tiny pores. Eggshell is made almost entirely of calcium carbonate (CaCO3) crystals. It is a semi-permeable membrane, which means that air and moisture can pass through its pores. The shell also has a thin outermost coating called the bloom or cuticle that helps keep out bacteria and dust.

Inner and Outer Membranes
Lying between the eggshell and egg white, these two transparent protein membranes provide efficient defense against bacterial invasion. If you give these layers a tug, you’ll find they’re surprisingly strong. They’re made partly of keratin,
a protein that’s also in human hair.

Air Cell
An air space forms when the contents of the egg cool and contract after the egg is laid. The air cell usually rests between the outer and inner membranes at the egg’s larger end, and it accounts for the crater you often see at the end of a hard-cooked egg. The air cell grows larger as egg ages

Albumen
The egg white is known as the albumen, which comes from albus, the Latin word for “white.” Four alternating layers of thick and thin albumen contain approximately 40 different proteins, the main components of the egg white in addition to water.

Chalazae
Opaque ropes of egg white, the chalazae hold the yolk in the centre of the egg. Like, little anchors, they attach the yolk’s casing to the membrane lining the eggshell. The more prominent they are, the fresher the egg.

Vitelline Membrane
The clear casing that encloses the yolk.

Yolk
The yolk contains less water and more protein than the white, some fat, and most of the vitamins and minerals of the egg. These include iron, vitamin A, vitamin D, phosphorus, calcium, thiamine, and riboflavin. The yolk is also a source of lecithin, an effective emulsifier. Yolk colour ranges from just a hint of yellow to a magnificent deep orange, according to the feed and breed of the hen.

USES OF EGG IN COOKERY

Various forms of using eggs in food preparation are:

Binding
Addition of eggs to minced mead and mashed vegetables etc. helps to bind the mixture. As the heat coagulates, the proteins are bound into a cohesive mass. It helps to retain the shape of mutton croquettes, meat loaf, medallions, hamburgers, etc.

Coating
The egg and egg batter help to give a coat to the food items and prevent them from disintegrating and give them a protective coating. Many of the food items such as fish fillets, croquettes, etc. are dipped into the batter before crumbing and then fried. Eggs are also used for preparing pancake batters.

Leavening
By beating the egg whites, foam is made up of air bubbles, surrounded by a thin elastic film of egg white. The mixture, when added to products such as sponge cakes, meringues, souffles, etc., increases the volume and the egg white film hardens. Addition of sugar to egg white makes it stable, smooth, and the foam does not collapse easily. Egg yolk has a less foaming power because of its fat content. An egg is used as the principal ingredient for Chou paste from which eclairs, beignets, fritters, and profiteroles are made.

Emulsifying
Eggs form stable emulsions. For example, mayonnaise, oil, and vinegar separate out unless oil droplets are coated with a substance that keeps them from separating. Eggs are the emulsifiers that give a smooth mayonnaise sauce. It is also used as an emulsifier in ice creams, cakes, cream puffs. Eggs enhance colour and shine.

Thickening
Eggs help to improve the consistency of gravies, curries, sauces, and soups. Egg liaisons used in soups and sauces help to thicken and improve consistency. When used in custards, the heat coagulates the eggs and makes the custard firm.

Decoration and Garnishing of Dishes
Silver, sieved or quarters of boiled eggs are used to decorate or garnish dishes such as salads, biryanis, curries, Vienna steaks, etc. For Consomme Xavier, threaded eggs are added as a garnish.

Clarifying
Consomme are clarified with egg whites.

Nutritional Value of an Egg
Eggs provide a significant amount of protein to one’s diet, as well as various nutrients. Chicken eggs are the most commonly eaten eggs and are highly nutritious. They supply a large amount of complete, high-quality protein (which contains all essential amino acids for humans), and provide significant amounts of several vitamins and minerals, including vitamin A, riboflavin, folic acid, vitamin B6, vitamin B12, choline, iron, calcium, phosphorus, and potassium.

They are also one of the least expensive single-food sources of complete protein. One large chicken egg contains approximately 7 grams of protein. All of the egg’s vitamin A, D, and E are in the egg yolk. The egg is one of the few foods which naturally contain Vitamin D. A large yolk contains more than two-thirds of the recommended daily intake of 300 mg of cholesterol.

COMMODITIES: SHORTENING (FATS & OILS)

Fats are solid at room temperature and melt when heated. Those used in cooking include butter, margarine, lard, suet, and hydrogenated fat.

Oils are liquid at normal temperatures but solidify at lower temperatures. Those commonly used in cooking are peanut (groundnut/arachide) oil, coconut oil, mustard seed oil, sesame (till) oil, olive oil, and safflower oil.

Shortenings of fats that are used in the baking industry and confectionery.

Hydrogenation Of Oils
The conversion of oil into fat is known as hydrogenation. The process changes the physical properties of the oil.
Hydrogenation consists of treating oil under suitable pressure and temperature with hydrogen, in the presence of a catalyst, usually Nickle (Ni). Under these conditions, the unsaturated fatty acids present in the oil combines with the hydrogen. This chemical process brings about a physical change and the liquid oil change into solid fat. The unsaturated fatty acids are chiefly those of the oleic type and are converted into solid stearic acid. The varying consistencies available in fats is due to the process of hydrogenation being stopped at various stages.

Shortenings
Fats can be used as shortenings or as a cooking medium. In confectionery, fats impart their characteristic flavor as well as shortening qualities. Their effect is to coat and break down the gluten strands, so that instead of being hard and tough to eat, foods containing shortening break off short and melt readily in the mouth.

Factors to look for in Shortenings:

Creaming Value
This affects the volume of the item eg: cakes. The amount of air incorporated during creaming increases the volume of the item.

Shortening value
The shortness gives to the end product. Shortness is a quality essential in products such as biscuits & cookies.

Stability
Refers to keeping quality and shelf life.

Consistency
Hardness or Softness depending on the purpose. Hardness for puff pastry and softness for cakes.
Water absorption will also affect the emulsification value of the shortening.

Power
As for shortening agents, fats add to the nutritional and satiety values of flour mixtures like doughs and batters. They also contribute to the taste and flavor. The type of fat and the way it is incorporated will affect the texture (eg: shortcrust pastry and flaky pastry). Baking must be done at correct temperatures. As the fat melts during baking, it must be absorbed by the flour. If the heat is insufficient, the melted fat will run out and result in a hard product. Fat which has been broken up into small particles during creaming will be more easily absorbed than fat left in large pieces.

Fat as a frying medium

Fat as a frying medium function in three ways:

• It serves to transmit heat to the articles of food to be fried.
• It adds to the nutritive value (calories).
• It contributes to the flavor and taste and texture of the food.

Fat used as a frying medium must have:

• High smoke point
• Low congealing point
• Low moisture content
• High stability
• The acceptable flavor which is neutral