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/fishSource of HBV protein for lacto-vegetariansRestrict on low calorie or low cholesterol dietsEasily digested therefore good for invalids, children, elderlyShould be served with food rich in complex carbohydrates, fibre and vitamin C
5 Egg structureShell = calcium carbonate, shell is porous so air, bacteria, smells and flavours can get in and water vapour can get outShell pores are covered by a natural varnish when laid2 membranes - one stuck to the shell and one surrounding the whiteAir space at rounded end of the egg between shell and membraneWhite/ albumin - 2 layers thin and thickYolk membraneChalazae hold yolk in centre of white for protectionYolk
6 Fresh eggs Heavy for size Rough shell Domed yolk Thick white Sinks in waterDate stampSmall air spaceNo bad smell when cracked
7 Grading eggs Graded by weight and quality Weight from size 1-7, size 1=70g size 7=45gQuality decided by candlingExtra sticker = within 7 days of laying should be removed when 7 days is over.Class A = best, small air space, poaching frying boilingClass 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 turnoverClass A, B or extraSize 1-7Check shellsCheck date stampHeavy with rough shellStorageStore at 7-13ºC e.g. fridge door, for 1 month.Away from strong smelling foodRounded end upLeft over egg white, air tight container in fridgeLeft over yolk, covered with water in fridgeRemove from fridge 1 hour before use
9 Quality assured eggsIreland 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 clumpstogether squeezes out the water andthis causes curdling.Coagulation is used when eggs are boiled,poached, scrambled, fried or turned into omelettes or custards. When eggs areused to thicken, bind, glaze, coat theprinciple 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. EmulsificationLecithin 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 eggsEgg protein denaturates and coagulates causing it to set and harden, egg white becomes opaqueShrinkSulphur 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 eggsDestroys pathogenic bacteria like salmonella.Loss of B group vitamins especially vitamin B1Too much heat causes curdlingIf overcooked white becomes tough and rubbery, yolk becomes dry and crumblyEgg 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 eggEffects: White is cloudyHarder to whiskCost moreKills harmful bacteriaAllows children, pregnant women, elderly, invalids to eat raw egg products without risk of food poisoning