俄亥俄州大学：《食品科学》课程教学资源（PPT课件，英文版）Chapter 7 Eggs

Chapter 7

Chapter 7 Eggs

Composition of eggs %o Water Protein Fat CHo Whole10074.612.11121.2 White5888010.10.20.8 Yolk3148.016432.92.0

Composition of eggs % Water Protein Fat CHO Whole 100 74.6 12.1 11.2 1.2 White 58 88.0 10.1 0.2 0.8 Yolk 31 48.0 16.4 32.9 2.0

Composition of eggs egg white(albumen) Water(w88% 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) • 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 ucin(\ 5lo): A Fibrous Protein. contributes to the thickness of the white( 4X more abundant than in yolk, contributes to the stability of egg white foam

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%0: 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 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%0: livetin LDL (protein content N 10%0) granular fraction phosvitin(16%0 carrier of Fe), lipovitellins(70%0 )& LDl (12%) Water(48%0

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 o Lipids (32 to 34%) triglycerol(66%0) 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

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)

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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 • 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 water evaporates from the egg through shell The egg white becomes thinner ovomucin undergoes degradation pH of white increases (from N 8 to v 9) due to the loss of Co2 through the pores

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