1. Eggs
© PDST Home Economics

2. Nutritive value of eggs
Protein: 13%, HBV, albumin & globulin in white, livetin & vitellin in yolk.
Fat: 12%, saturated, in yolk, in fine emulsion because of lecithin, easy to digest, high in cholesterol.
Carbohydrate: 0%, serve with complex carbohydrates, no fibre present.

3. Vitamins: A & D in yolk, B2,Niacin and B12 ( more in free range)
Vitamins: A & D in yolk, B2,Niacin and B12 ( more in free range). Lack vitamin C.
Minerals: 1%,Calcium and phosphorus useful amounts, iron in yolk.
Water: 74%, more in white than yolk.
Energy: 147 kcal, mostly in yolk.

4. Dietetic value of eggs Cheap & nutritious, low budgets Versatile
Protein alternative to meat/fish
Source of HBV protein for lacto-vegetarians
Restrict on low calorie or low cholesterol diets
Easily digested therefore good for invalids, children, elderly
Should be served with food rich in complex carbohydrates, fibre and vitamin C

5. Egg structure
Shell = calcium carbonate, shell is porous so air, bacteria, smells and flavours can get in and water vapour can get out
Shell pores are covered by a natural varnish when laid
2 membranes - one stuck to the shell and one surrounding the white
Air space at rounded end of the egg between shell and membrane
White/ albumin - 2 layers thin and thick
Yolk membrane
Chalazae hold yolk in centre of white for protection
Yolk

6. Fresh eggs Heavy for size Rough shell Domed yolk Thick white
Sinks in water
Date stamp
Small air space
No bad smell when cracked

7. Grading eggs Graded by weight and quality
Weight from size 1-7, size 1=70g size 7=45g
Quality decided by candling
Extra sticker = within 7 days of laying should be removed when 7 days is over.
Class A = best, small air space, poaching frying boiling
Class B = large air space, staler, yolk off centre, scrambling, baking, sauces.
Class C = similar to class B but sold only to food manufacturers.

8. Buying and storing eggs
Free range cost more.
Quick turnover
Class A, B or extra
Size 1-7
Check shells
Check date stamp
Heavy with rough shell
Storage
Store at 7-13ºC e.g. fridge door, for 1 month.
Away from strong smelling food
Rounded end up
Left over egg white, air tight container in fridge
Left over yolk, covered with water in fridge
Remove from fridge 1 hour before use

9. Quality assured eggs
Ireland has an EU approved salmonella plan to maintain the health of the country’s laying stock.
Incoming hens must be certified as salmonella free.
Laying hens are checked for salmonella on a monthly basis.
All feed for hens is heat treated.
Management systems ensure full traceability of eggs.
Eggs carry best before date and house code and logo.
All producers and suppliers are inspected and approved.
All systems are independently inspected before QA mark is awarded.

10. Properties of eggs 1. Coagulation
Egg protein coagulates and sets when heated. White 60-65ºC. Yolk ºC.
Coagulation causes the protein chains to untwist and straighten (denature) and bond together around small pockets of water.
When overheated the protein clumps
together squeezes out the water and
this causes curdling.
Coagulation is used when eggs are boiled,
poached, scrambled, fried or turned into omelettes or custards. When eggs are
used to thicken, bind, glaze, coat the
principle of coagulation is used.

11. 2. Aeration/Entrapping air
Whisking egg or just egg white brings bubbles of air into a mixture.
Whisking also causes heating of the egg protein (by friction) which slightly sets the protein chains and makes them unravel and line up around the air bubbles.
This causes a temporary foam to form.
To keep the foamy texture permanently in place the mixture must be further heated or a setting agent like gelatine must be added.
Aeration is used to make meringues and souffles.

12. 3. Emulsification
Lecithin in egg yolk is an emulsifier.
An emulsifier is a substance that causes mixtures that would normally separate (e.g. vinegar and olive oil) to stay mixed together.
This property is used in making mayonnaise and hollandaise sauce.

13. Uses of eggs in food preparation
Binding: sticking ingredients together e.g. burgers, fish cakes (coagulation).
Coating: protects food when frying, egg is used to stick a layer on outside of food e.g. breaded fish (coagulation).
Glazing: beaten egg brushed on baked foods to make them brown and shiny e.g. scones (coagulation).
Thickening: e.g. custard sauce (coagulation).
Enriching: increasing the nutritive value of a dish e.g. brown bread.
Garnishing: hard boiled egg sliced or chopped for decoration e.g. salad or dressed crab.
Emulsifying: e.g. mayonnaise, hollandaise sauce.
Aerating: e.g. sponge cake, meringue.
Clarifying: egg whites used to make jelly, stock or wine clear (coagulation).

14. Effects of heat on eggs
Egg protein denaturates and coagulates causing it to set and harden, egg white becomes opaque
Shrink
Sulphur in egg white protein reacts with iron in yolk to form iron sulphide which causes the greenish colour on outside of the yolk of hardboiled eggs
Destroys pathogenic bacteria like salmonella.
Loss of B group vitamins especially vitamin B1
Too much heat causes curdling
If overcooked white becomes tough and rubbery, yolk becomes dry and crumbly
Egg albumin (white) which is soluble in cold water becomes insoluble

15. Pasteurisation of eggs
This involves slowly heating whole raw eggs to kill harmful bacteria without cooking the egg
Effects: White is cloudy
Harder to whisk
Cost more
Kills harmful bacteria
Allows children, pregnant women, elderly, invalids to eat raw egg products without risk of food poisoning