The egg

Aug. 23, 2015

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The egg

  1. The Egg BFST 2203 Food Proteins and Hydrocolloids Gihan Wijelath Taniya Nanayakkara Shamara Perera Sachini Bhagya
  2. Content • Introduction • Structure of an egg • Protein content • Types of protein present in egg white & yellow • Production of egg powder
  3. Introduction • Eggs are laid by female animals of many species including birds, amphibians, reptiles and fish • Chicken eggs are the most popular choice of egg consumption • They an inexpensive source of protein • Used as a reference standard against which all other protein containing foods are assessed
  4. Structure of an Egg An egg basically consists of three parts: • Shell • Egg white • Egg yolk
  5. Structure of an Egg
  6. Structure of an Egg Eggshell • The outer eggshell is made almost entirely of calcium carbonate (CaCO3) and is covered with as many as 17,000 tiny pores. • It is a semipermeable membrane, which allows air and moisture to pass through its pores. • The shell also has a thin outermost coating called the bloom or cuticle that helps keep out bacteria and dust . Outer and inner shell membrane • These two membranes are inside the shell surrounding the albumen (white).
  7. Structure of an Egg • The two membranes are made partly of keratin and provide an efficient defense against bacterial invasion. • The outer membrane sticks to the egg shell while the inner membrane sticks to the albumen. Chalazae • Strands that are twisted in opposite directions and anchor the yolk in center of the egg. The more prominent the chalazae, the fresher the egg. Exterior albumen (outer thin albumen) • The outer thin albumen; a narrow fluid layer next to the shell membrane.
  8. Structure of an Egg Middle albumen (inner thick albumen) • The inner thick white (chalaziferous layer) is a dense, matted, fibrous capsule of albumen around the vitelline membrane of the yolk. • An excellent source of riboflavin and protein. • In high-quality eggs, the inner thick albumen stands higher and spreads less than thin white. In low-quality eggs, it appears thin white. Vitelline membrane • Clear seal which holds the egg yolk
  9. Structure of an Egg Yellow yolk • The yolk contains less water and protein than the white, some fat, and most of the vitamins and minerals of the egg. • It is also a source of lecithin; an effective emulsifier. • Yolk color ranges from just a hint of yellow to a magnificent deep orange, according to the feed and breed of the hen. Air cell • An air space forms when the contents of the egg cool and contract after the egg is laid.
  10. Structure of an Egg • The air cell rests between the outer and inner membranes at the eggs larger end. • As the egg ages, moisture and carbon dioxide leave through the pores of the shell, air enters to replace them and the air cell becomes larger. Germinal disk (blastoderm) • A small, circular, white spot (2-3 mm across) on the surface of the yolk; it is where the sperm enters the egg. • The embryo develops from this disk, and gradually sends blood vessels into the yolk to use it for nutrition as the embryo develops.
  11. Protein Content of an Egg • Protein content of an egg accounts to about 12.6% by weight of the edible portion Distribution of proteins in an egg Egg white 57% Egg yellow 43%
  12. Table: Protein content of eggs Description Protein Content (per 100g) Protein Content (%) Egg,whole,raw,fresh 12.56g 12.56% Egg,white,raw,fresh 10.90g 10.90% Egg,yolk,raw,fresh 15.86g 15.86% Egg,whole,dried 48.37g 48.37% Egg,whole,cooked,hardboiled 12.58g 12.58% Egg,whole,cooked,fried 13.61g 13.61% Egg,whole,cooked,omelet 10.57g 10.57% Source: National Nutrient Database for Standard Reference Release 27 (2014), United States Department of Agriculture
  13. Protein Content of an Egg • Contains all essential amino acids • Rich in essential amino acid leucine • Composition of amino acids in an egg matches the requirement of amino acids by the human body
  14. Types of Protein Present in Egg White and Egg Yellow Egg White • Egg white consists of about 90% water in which about 10% of proteins is dissolved. • Egg white is an alkaline solution which contains approximately 40 different proteins.
  15. Types of Proteins Present in Egg White • 54% Ovalbumin • 12% Ovotransferrin • 11% Ovomucoid • 4% Ovoglobulin G2 • 4% Ovoglobulin G3 • 3.5% Ovomucin • 3.4% Lysozyme • 1.5% Ovoinhibitor • 1% Ovoglycoprotein • 0.8% Flavoprotein • 0.5% Ovomacroglobulin • 0.05% Avidin • 0.05% Cystatin
  16. Ovalbumin • Ovalbumin is an almost spherical glycophosphoprotein which is the most common protein in egg white. Figure 1. Crystal structure of ovalbumin Source: Roth, K; Available from: • Storage protein
  17. Ovotransferrin • Composed of 686 amino acids • Consists of 2 forms which contains neither phosphorus nor sulfur • Disulfide crosslinks are present • Has antimicrobial and iron-binding ability Figure: Crystal structure of ovotransferrin Source : Dong,A , Egg Components
  18. Ovomucoid • Ovomucoid is a glycoprotein • Consists of 9 disulphide bonds • Has a stable spatial structure that it is not denatured even upon boiling Figure: Crystal structure of ovomucoid Source: Roth, K; Available from:
  19. Types of Proteins Present in the Egg Yolk • The major proteins in egg yolk are lipoproteins  Livetin  Lipovitellin  Phosvitin
  20. Phosvitin • A type of phosphoprotein • About 16% egg yolk proteins • Consists of about 10% phosphorus • Has iron and calcium binding capacity Figure: Crystal structure of phosvitin Source:
  21. Production of egg white powder
  22. Powdered egg whites are simply egg whites that have been dehydrated and ground into a powder. Powdered egg whites or egg white powder are also sold as spray-dried egg whites and spray- dried albumin. Since egg white is often taken as a supplement, it is also sold as "egg white protein" or "egg white protein powder,".
  23. Egg breaking and Egg white separating Filtering Separating Tank storage and pH fit Reverse osmosis Fermentation Spray drying Chilling Dry heating
  24. The first step in the process is the breaking of the eggs. There are 3 main fractions egg white egg yolk whole egg The white fraction is the one used for the production of albumen powder. The fractionation is achieved by breaking the egg over a small cup which only holds the egg yolk allowing for a vessel under this cup to collect the egg white.
  25. The egg white is then filtered to get rid of any residual pieces of egg shell or other large contaminants. Afterwards it is pumped to storage tanks where the pH is adjusted, using citric acid, and stored until the egg white is to be used in the production. Next the egg white is transferred to a separator which further separates any remnants of egg shell or other physical residues. The egg white is subjected to a reverse osmosis treatment which increases the dry weight.
  26. After the concentration the next goal of the process is to break down the glucose and fat present in the egg white. • Glucose - add either enzymes or bacteria • Fat - add lipase This procedure is performed in fermentation tanks. Time required- 24 hrs Glucose content should be monitored.
  27. After fermentation pH is corrected using lactic acid. The egg white is then pumped to a cooling tank where the temperature is lowered to 4 degrees Celsius.- chilling
  28. Finally the liquid egg white is transformed into albumen powder using a box spray dryer. -spray drying Last step in the process is dry heating in large conical dry blenders (87 degrees Celsius for 12 hours ) [Elimination of microbial threat- salmonella]
  29. Advantages of egg white powder • Can be stored and transport in room temperature. • Good shelf life • Time saving • Can store in smaller space • Requires no refrigeration
  30. References The Anatomy of a Chicken Egg [online] available at anatomy-of-a-chicken-egg/ (accessed on 12th August 2015) Structure of the egg [online] available at (accessed on 12th August 2015) National Nutrient Database for Standard Reference Release 27 [online](2014), available at
  31. American egg board[online]available at overview/egg-products-specifications/45-egg-white-types/139- driedrd;accessed 11th august 2015 discoloration of albumen powder; [online]available at coloration_of_egg_white_powder_final.pdf; accessed on 11th august 2015
  32. Thank you