Chapter 7 Eggs Composition of eggs Composition of

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Chapter 7 Eggs

Chapter 7 Eggs

Composition of eggs

Composition of eggs

Composition of Eggs egg white (albumen) · · Water (~88%) CHO (~1%) -mainly glucose,

Composition of Eggs egg white (albumen) · · Water (~88%) CHO (~1%) -mainly glucose, may cause brown discoloration in dried eggs and hard cooked eggs (Millard reaction) · Fat (trace)

Composition of Eggs egg white (albumen) · Proteins (~11%), most are glycoproteins -Three primary

Composition of Eggs egg white (albumen) · Proteins (~11%), most are glycoproteins -Three primary proteins: - ovalbumin (54%) Structure of Baked Products ovotransferrin (12%), Binds metal, Discoloration ovomucoid (11%) Protease Inhibitor - ovomucin (1. 5%): A Fibrous Protein, contributes to the thickness of the white (4 x more abundant than in yolk), contributes to the stability of egg white foam

Composition of Eggs egg white (albumen) · Proteins (cont’n) ·globulins (8%): including lysozyme, are

Composition of Eggs egg white (albumen) · Proteins (cont’n) ·globulins (8%): including lysozyme, are important for foaming ·lysozyme: ability to hydrolyze a polysaccharide in the cell wall of some bacteria to prevent bacterial spoilage · others: ovoinhibitor, ovoflavoprotein, ovomicroglobulin, avidin (binds biotin, but is heat sensitive)

Composition of Eggs egg yolk · Proteins (16. 4%): plasma (78%): livetin & LDL

Composition of Eggs egg yolk · Proteins (16. 4%): plasma (78%): livetin & LDL (protein content ~ 10%) · granular fraction: phosvitin (16%, carrier of Fe), lipovitellins (70%) & LDL (12%) · · Water (48%)

Composition of Eggs egg yolk ·Lipids - (32 to 34%) triglycerol (66%) phospholipid (28%)

Composition of Eggs egg yolk ·Lipids - (32 to 34%) triglycerol (66%) phospholipid (28%) including lecithin (has remarkable emulsifying ability) cholesterol (3%, or 250 mg) ·The color of yolk depends on the presence of carotenoids. · xanthophylls not carotene (Lutein and zeaxanthin)

Egg Quality Commercial grading of eggs according to the USDA standards · External quality:

Egg Quality Commercial grading of eggs according to the USDA standards · External quality: shell characteristics, shape, soundness, cleanliness, & color · Interior quality: size of the air cell, firmness of the white, & the yolk (distinct or flattened during aging) · Evaluated by candling ·

Egg quality during storage · The size of the air cell increases - ·

Egg quality during storage · The size of the air cell increases - · The egg white becomes thinner - · water evaporates from the egg through shell ovomucin undergoes degradation p. H of white increases (from ~ 8 to ~9) - due to the loss of CO 2 through the pores

Egg quality during storage ·The yolk enlarges and the membrane weakens (water moves from

Egg quality during storage ·The yolk enlarges and the membrane weakens (water moves from white to yolk, viscosity decreases, yolk becomes flatter and spreads farther) · · Deterioration of odor & flavor Increased storage temperature accelerates loss of quality

Functionality of Eggs n Coagulation n Emulsification n Foaming

Functionality of Eggs n Coagulation n Emulsification n Foaming

Functionality of Eggs: Coagulation or Gelation

Functionality of Eggs: Coagulation or Gelation

Protein Coagulation Denaturation: Relaxation of the tertiary structure to the secondary structure, accompanied by

Protein Coagulation Denaturation: Relaxation of the tertiary structure to the secondary structure, accompanied by decreasing solubility of a protein n Precipitation of protein as molecules aggregate (often as a result of energy input, such as heating or beating) n Process that results in a loss of solubility or a change from a fluid state to a solid state. (Gelation is also used to describe the process. n

Functionality of Eggs coagulation n egg white begins to thicken at ~62 o. C,

Functionality of Eggs coagulation n egg white begins to thicken at ~62 o. C, yolk at ~65 o. C. 72 o. C Firm The gel firmness depends on time & temperature of heating n Gel hardness dependents on the p. H and the concentration of protein n increased p. H or protein will increase gel hardness n diluted protein will increase coagulation temperature ∟ n

Functionality of Eggs coagulation Sugar decreases the rate of heat denaturation & increases the

Functionality of Eggs coagulation Sugar decreases the rate of heat denaturation & increases the coagulation temperature n Salts promote coagulation n

Functionality of Eggs

Functionality of Eggs

Functionality of Eggs emulsification n Formation of emulsion • • n mechanical agitation makes

Functionality of Eggs emulsification n Formation of emulsion • • n mechanical agitation makes it insoluble and stiff or stable emulsifying agent (Lecithin) Egg Yolk is an oil-in-water emulsion

Functionality of Eggs: Foaming

Functionality of Eggs: Foaming

Functionality of Eggs foaming A colloidal suspension: bubbles surrounded by egg albumen (protein) n

Functionality of Eggs foaming A colloidal suspension: bubbles surrounded by egg albumen (protein) n globulins have greater foaming ability n ovomucin stabilizes the foam n

Functionality of Eggs factors affecting foaming n Method, time and temperature of beating as

Functionality of Eggs factors affecting foaming n Method, time and temperature of beating as beating time increases, volume and stability of the foam 1 st increases then decreases n maximum stability is reached before maximum volume n room temperature vs refrigerator temperature n

Functionality of Eggs factors affecting foaming n Characteristics of the egg white thin white

Functionality of Eggs factors affecting foaming n Characteristics of the egg white thin white vs thick white n stored eggs vs fresh eggs n n p. H n acids or acid salts increases foam stability but delays foam formation

Functionality of Eggs factors affecting foaming n Water n n fat n n water

Functionality of Eggs factors affecting foaming n Water n n fat n n water increases the foam volume but decreases its stability oil reduces foam volume sodium chloride n reduces the foam stability, increases whipping time

Functionality of Eggs factors affecting foaming n Sucrose n n n egg yolk n

Functionality of Eggs factors affecting foaming n Sucrose n n n egg yolk n n delays foam formation (so beat then add) produces a more stable foam decreases the foam volume additives n surfactants and stabilizers may reduce whipping time, increase foam volume

Functionality of Eggs

Functionality of Eggs

Functionality of Eggs factors affecting foaming n n n n Method, time and temperature

Functionality of Eggs factors affecting foaming n n n n Method, time and temperature of beating characteristics of the egg white p. H water and fat sodium chloride sucrose egg yolk additives

Functionality of Eggs

Functionality of Eggs

Processed Eggs n Frozen eggs egg whites perform well after freezing & thawing n

Processed Eggs n Frozen eggs egg whites perform well after freezing & thawing n add 10% (w/w) of sugar or salt to yolks before freezing to control the gelation of frozen yolk n To prevent “syneresis” in frozen cooked egg products: n • addition of gums • addition of citric acid • addition of salt

Processed Eggs n Egg substitutes use of egg white together with a yolklike mixture

Processed Eggs n Egg substitutes use of egg white together with a yolklike mixture containing no cholesterol n fortify with fat-soluble nutrients n addition of carotenoid for giving the yolk color n addition of carboxymethyl-cellulose (CMC) reduces weeping n aroma and flavor are not as good as fresh eggs n

Processed Eggs n Dried eggs (spray drying) products: whole-egg solids, yolk solids, fortified whole-egg

Processed Eggs n Dried eggs (spray drying) products: whole-egg solids, yolk solids, fortified whole-egg solids and whites n growth of microorganisms is inhibited n coagulation is not affected n foaming potential is reduced n add whipping agents (surface active) n

Processed Eggs All liquid eggs should be pasteurized (61 C for 3. 5 min)

Processed Eggs All liquid eggs should be pasteurized (61 C for 3. 5 min) to kill salmonella and other potential pathogens. n Ultrapaseurized liquid whole eggs n retain functional properties of fresh shell eggs n are aseptically packaged n

Functionality of Eggs: Summary · · coloring agent (carotenoids in yolk) emulsifier ·mayonnaise, ·

Functionality of Eggs: Summary · · coloring agent (carotenoids in yolk) emulsifier ·mayonnaise, · thickening agent (coagulation) - · hollandaise sauce, cream puff baked (gel) or stirred (sol) custards, foaming meringues, foam cakes (angel, sponge, and chiffon) -

Proverbs 12: 15 The Way of a Fool Seems right to Him BUT a

Proverbs 12: 15 The Way of a Fool Seems right to Him BUT a Wise Man Listens to Advice