Proteins

1. Proteins • POLYMERIZATION or AGGREGATION reactions that involve the formation of large protein complexes • PRECIPITATION includes all reactions that lead to a total or partial loss of solubility • FLOCCULATION refers to the random aggregation in the absence of denaturation

2. PROTEINS • COAGULATION refers to the random aggregation of proteins that involves denaturation • GELATION refers to the process of formation ordered protein network by denatured proteins

3. FOOD PROTEINS • FOOD PROTEINS ARE PROTEINS THAT ARE PALATABLE, DIGESTABLE, NONTOXIC, AND AVAILABLE ECONOMICALLY FOR HUMANS.

4. Denaturation • Any process/treatment that brings about change in molecular structure of protein without breaking covalent bonds

5. Denaturation of protein may brings about: • Decreased solubility • altered water binding capacity • loss of biological activity • increased susceptibility to attack by protease due to unmasking of peptide bonds • inability to crystallize

6. Denaturing agents: • Physical: heat, cold, mechanical treatment, interface, hydrostatic pressure, radiation • Chemical: acids, alkali, organic solvents, solution of organic compounds (urea, guanidine-disrupt hydrogen bonds; ascorbic acid and b-mercaptoethanol -reduces disulphide crosslinks)

7. Sensitivity of protein to heat depends on: • Nature of protein • protein concentration • water activity • pH • ionic strength • kind of ions present

8. Coagulation temperature (O C )

9. EGGS • Average weight 57g • shell 11% • albumen (egg white) 56% • yolk 31%

10. Shell • It contains 94% of calcium carbonate, 1% magnesium carbonate, 1% calcium phosphate and 4% organic matter. • Shell membrane has two layers • The conditions of shell membrane and shell affect: loss of carbon dioxide, loss of moisture, shell breaking strength, susceptibility to microbial invasion

11. Yolk consists of: • Latebra • germinal disc • concentric discs of light and dark yolk materials • vitelline membrane

12. Albumen • Very firm but thin chalaziferous layer (3%) that surrounds yolk and is continuous with chalazae - a cord-like strands (mucins) on each side of yolk • Inner thin layer (17%) • firm or thick layer (57%) -envelope to hold egg yolk and outer thin layer in place • outer thin layer (23%)

13. Changes in quality of eggs • Thick albumen become less viscous. This thinning may be caused by proteolysis, reduction of S-S bonds, interaction of ovomucin and lysozyme • yolk is flatten • pH of albumen 7.6  8.9-9.4 • pH of yolk 5.9-6.1  6.8

14. Changes in egg quality • Losses of CO2 depend on storage tempe- rature, partial pressure of CO2 in the atmo- sphere, permeability of shell. • Losses of moisture depend on storage temperature, relative humidity, shell treatment (spraying or dipping egg in mineral oil)

15. Flavour of egg may be affected by: • Diet: fish oil, fish meal, linseed oil • storage of eggs near odorous substances • washing solution

16. Colour • Fresh egg white - opalescent, greenish cast due to the presence of riboflavin, old -clearer • yolk colour -ranges from very pale through deep yellow to deep orange. Color due to the presence of carotenoids (xanthophylls)

17. Discoloration of eggs: • Pink albumen -due to diffusion of iron from yolk and formation of Fe-conalbumin complex. • Salmon colored yolk results from a pink color combined with natural yellow color of yolk • related to feeds - cottonseed meal increases permeability of vitelline membrane.

18. Albumen • 30mL (88% water, 10.1% proteins, 1.2% sugars, 0.6% ash) • 40 proteins, but only six at >1% • functional and nonfuctional proteins • Ovalbumin, globulins, conalbumin (ovotranferrin), ovomucin, ovomucoid

19. Albumen proteins

20. Albumen proteins • Ovalbumin 54% • globulins 11.5-13% • conalbumin 13% • ovomucin • ovomucoid

21. Functional properties of egg proteins • Coagulation • Gelation • Foaming

22. Coagulation and gelation • At moderate heating rate egg white become opaque at 60C and firmer at 75 • whole egg thicken at 65 but solidifies at 70C • conalbumin the least heat stable protein 57.3C • Globulins and ovalbumin 72C • lysozyme 81.5C • ovomucin and ovomucoid >90C

23. Coagulation and gelation • Ovomucoid increases coagulation temperature of globulins and lysozyme • conalbumin decrease the coagulation temperature • phosvitin is heat stable (100C few hours) • lipovitellins (pH 4-5, 70C) (pH higher, >80C); addition of lysozyme and ovalbumin increases gel strength.

24. Coagulation of albumen proteins

26. Doneness of cooked shell eggs depends on: • Initial temperature of water and egg • the quantity of water in relation to the size of egg • the rate of heating • 25-35 min at 85-90 • >12 min at 98-100 • pelling difficult if pH of egg white is less than 8.5

27. Foaming • Foam stiffnessis judged by overall appea- rance, the height of peaks, the extent to which the peak bends when beater is removed, the rate of flow when the container is partially inverted. • Foam stability is determined by measuring the drainage from the foam in a given time • Beating rate is the ratio of specific volume to the beating time (ml/sec].

28. Foaming • Whipping ability of egg white depends on ovalbumin and globulins • foam stability depends on ovomucin

29. Egg processing • Pasteurization • Freezing • Dehydration

30. Pasteurization - albumen (60-61 C for 3.5 min] • pH adjusted to 6.8-7.8 (lactic acid) + aluminum sulfate • pH adjusted to 8.5-9.0 + hydrogen peroxide • heat and vacuum • pH adjusted to 10.5 and heating at 55C

31. Desugarization

32. Dehydration - albumen • Spray drying • film drying on continuous belt • drying diminish foaming properties • addition of sugar improve retention of flavour.

33. Freezing • Albumen - no concerns • yolk addition of 10% sugar or salt needed to prevent gelation