Proteins

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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

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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

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FOOD PROTEINS

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

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Denaturation

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

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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

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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)

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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 )
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EGGS

• Average weight 57g
• shell 11
• albumen (egg white) 56
• yolk 31

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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)

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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

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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)

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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.

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Albumen

• 30mL (88 water, 10.1 proteins, 1.2 sugars,
  0.6 ash)
• 40 proteins, but only six at gt1
• functional and nonfuctional proteins
• Ovalbumin, globulins, conalbumin (ovotranferrin),
  ovomucin, ovomucoid

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Albumen proteins
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Albumen proteins

• Ovalbumin 54
• globulins 11.5-13
• conalbumin 13
• ovomucin
• ovomucoid

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Functional properties of egg proteins

• Coagulation
• Gelation
• Foaming

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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 gt90C

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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, gt80C)
  addition of lysozyme and ovalbumin increases gel
  strength.

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Coagulation of albumen proteins
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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
• gt12 min at 98-100
• pelling difficult if pH of egg white is less
  than 8.5

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Foaming

• Foam stiffness is 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.

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Foaming

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

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Egg processing

• Pasteurization
• Freezing
• Dehydration

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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

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Desugarization
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Dehydration - albumen

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

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Freezing

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