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Chapter 7

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Chapter 7

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  1. Chapter 7 Eggs

  2. Composition of eggs

  3. 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)

  4. 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

  5. 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)

  6. 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%)

  7. 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)

  8. 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

  9. Egg quality during storage The size of the air cell increases water evaporates from the egg through shell The egg white becomes thinner ovomucin undergoes degradation pH of white increases (from ~ 8 to ~9) due to the loss of CO2 through the pores

  10. 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

  11. Functionality of Eggs • Coagulation • Emulsification • Foaming

  12. Functionality of Eggs:Coagulation or Gelation

  13. Protein Coagulation • Denaturation: Relaxation of the tertiary structure to the secondary structure, accompanied by decreasing solubility of a protein • Precipitation of protein as molecules aggregate (often as a result of energy input, such as heating or beating) • 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.

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

  15. Functionality of Eggs -coagulation • Sugar decreases the rate of heat denaturation & increases the coagulation temperature • Salts promote coagulation

  16. Functionality of Eggs

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

  18. Functionality of Eggs:Foaming

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

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

  21. Functionality of Eggs - factors affecting foaming • Characteristics of the egg white • thin white vs thick white • stored eggs vs fresh eggs • pH • acids or acid salts increases foam stability but delays foam formation

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

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

  24. Functionality of Eggs

  25. Functionality of Eggs - factors affecting foaming • Method, time and temperature of beating • characteristics of the egg white • pH • water and fat • sodium chloride • sucrose • egg yolk • additives

  26. Functionality of Eggs

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

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

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

  30. Processed Eggs • All liquid eggs should be pasteurized (61C for 3.5 min) to kill salmonella and other potential pathogens. • Ultrapaseurized liquid whole eggs • retain functional properties of fresh shell eggs • are aseptically packaged

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

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