4 Eggs a) The physical structure and factors

affecting quality.b) Nature of egg proteins.

c) Processing of eggs to make:frozen whole egg

dried egg

Q

What category of macronutrient do eggs primarily come under?

A

What category of macronutrient do eggs primarily come under?

Protein

UK consumption

• In the UK, most people eat eggs which come from hens. It is also possible to eat eggs from geese, ducks and quails.

• Cheap, convenient and nutritious (HBV protein).

• Eat over 10 billion eggs a year in the UK• 86% of these eggs still come from

battery caged hens who do not have the freedom to express natural behaviour i.e. dust bathe, forage, roost & nest

Blastodisc

Ka-laze-i

Proteins in eggs

• Ovalbumin - 54% of an eggs total protein content.

• Conalbumin - 12% of the protein content. • Ovomucoid – 11% of the protein content.• Ovoglobulins G2 and G3 - 10% of the

protein content. • Lysozyme - 3.5% of egg white protein. • Ovomucin – 3% which is a jelly-like protein.• Avidin - 0.5% of egg white protein.• Few more to make it up to 100% but in much

smaller proportions.

Structure of eggs

• Outer shell composed mainly of calcium carbonate and a number of pores. Covered by a wax-like layer, known as cuticle.

• Cuticle protects against microbial invasion and controls water loss.

Structure of eggs

• Egg white is divided into thick around the yolk and thin next to the shell.

• The thick anchors the yolk with the chalazae.

• White foams readily therefore good for soufflés and meringues.

Structure of eggs

• Egg white – beating egg white can create a foam.

• The whisk drags the liquid through itself, creating a force that unfolds the protein molecules

• This process is called denaturation.

Structure of eggs

• Egg yolk rick in nutrients. Protein, fat (33%), water, Vitamin A, D, E, K and iron.

• Emulsifying properties – contains lecithin

• Mayo, salad dressing and cakes.

Laying cages- battery farming

Barn eggsBarn farming

Free range

Organic

Quality of eggs

• The air space in the egg will get larger as the egg gets older. This is because the shell of the egg is porous (able to absorb fluids). A stale egg will float in a bowl of water.

Quality of eggs

• Biological changes gradually take place inside the egg.

• Thick white of egg becomes thinner and membranes of yolk weaken.

• A fresh egg usually has an index of about 0.45 and this gradually falls on ageing as freshness decreases.

egg atits freshest, with arounded, plumpyolk that sits upproudly. The whitehas a thicker,gelatinous layerthat clings allaround the yolkand a thinner outerlayer. theyolk is flatter andthe two separatetextures of whiteare not quite sovisible.

Egg processing

• Frozen whole egg is produced on a large scale.

• Eggs washed and any bacteria destroyed.

• Eggs are broken mechanically and mixed to an homogeneous product which is pasteurized at 63oC for 60secs.

• Liquid egg is filled into cans and frozen.

Egg processing

• Dried egg is usually made by spray drying although freeze-drying produces an excellent but expensive product.

• Eggs are prepared as above and then spray dried in a drier and used for milk powder.

• Task: Using Proudlove, find out what freeze-drying and spray drying is.

Effect of heat

• Proteins in the egg white coagulates at 60oC becomes opaque and forms a gel.

• Egg yolk proteins at 70oC, yolk thickens.

• Whole egg between 60-70oC

• The cooking process 12mins 55secs

FunctionsFunction ExampleAdds colour and flavour Cakes

Holds air when whisked – ovalbumin can stretch

Meringues – light mixture

Cake - aeration

Forms an emulsion when mixed with fat – egg yolk contains lecithin

Mayonnaise

Binds ingredients together Beef burgers, fishcakes

Coagulating/setting Quiche

Glazing Pastry

Coating/enrobing Holding breadcrumbs on

Enriching/thickening Sauces

To give a smooth, glossy finish (enriching)

Choux Pastry

Storage

• Store in the fridge at 0-5oC• Used at room temp, don’t whisk well

when cold.

Lion MarkThe Lion Quality Mark shows that eggs have been produced to

the highest food safety standards

Jimmy's Food Factory Nov 2009

6mins - 12mins 40secs

Egg allergy

• A reaction to one or more  proteins and is most common in babies and young children under the age of one.

• About half of all children who are allergic to eggs will have grown out of it by the time they are three, and very few children still have an egg allergy after the age of six

• Rare, but sometimes egg allergy may not start until adulthood. Reaction to egg can also cause a rash around the mouth in addition to symptoms listed above.

Research Eggs

• www.britegg.co.uk• Jamie Oliver's Fowl Dinners• Using the above 2 sources, 1. Explain and account for trends in egg

production in the UK (6 marks)2. Some people say that only free range

eggs should be produced in the UK. Using your knowledge, evaluate the benefits and limitations of such a move. (8 marks)

3. Explain what the lion mark means to consumers. (2 marks)

Egg Questions

• Discuss the 3 sections of the egg and state the role of each layer (6 marks)

• Discuss the effect that heat has on egg protein (2 marks)

• Discuss how eggs are used in cooking (3 marks)