Chapter 7 Eggs Composition of eggs Composition of
- Slides: 34
Chapter 7 Eggs
Composition of eggs
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 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 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 (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%) 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: 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 - · 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 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: Coagulation or Gelation
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, 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 coagulation temperature n Salts promote coagulation n
Functionality of Eggs
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 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 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 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 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 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 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
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 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 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) 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, · thickening agent (coagulation) - · hollandaise sauce, cream puff baked (gel) or stirred (sol) custards, foaming meringues, foam cakes (angel, sponge, and chiffon) -
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