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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 PROTEINS

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proteins
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
proteins2
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
food proteins
FOOD PROTEINS
  • FOOD PROTEINS ARE PROTEINS THAT ARE PALATABLE, DIGESTABLE, NONTOXIC, AND AVAILABLE ECONOMICALLY FOR HUMANS.
denaturation
Denaturation
  • Any process/treatment that brings about change in molecular structure of protein without breaking covalent bonds
denaturation of protein may brings about
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
denaturing agents
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)
sensitivity of protein to heat depends on
Sensitivity of protein to heat depends on:
  • Nature of protein
  • protein concentration
  • water activity
  • pH
  • ionic strength
  • kind of ions present
slide9
EGGS
  • Average weight 57g
  • shell 11%
  • albumen (egg white) 56%
  • yolk 31%
shell
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
yolk consists of
Yolk consists of:
  • Latebra
  • germinal disc
  • concentric discs of light and dark yolk materials
  • vitelline membrane
albumen
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%)
changes in quality of eggs
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
changes in egg quality
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)
flavour of egg may be affected by
Flavour of egg may be affected by:
  • Diet: fish oil, fish meal, linseed oil
  • storage of eggs near odorous substances
  • washing solution
colour
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)
discoloration of eggs
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.
albumen18
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
albumen proteins20
Albumen proteins
  • Ovalbumin 54%
  • globulins 11.5-13%
  • conalbumin 13%
  • ovomucin
  • ovomucoid
functional properties of egg proteins
Functional properties of egg proteins
  • Coagulation
  • Gelation
  • Foaming
coagulation and gelation
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
coagulation and gelation23
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.
doneness of cooked shell eggs depends on
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
foaming
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].
foaming28
Foaming
  • Whipping ability of egg white depends on ovalbumin and globulins
  • foam stability depends on ovomucin
egg processing
Egg processing
  • Pasteurization
  • Freezing
  • Dehydration
pasteurization albumen 60 61 c for 3 5 min
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
dehydration albumen
Dehydration - albumen
  • Spray drying
  • film drying on continuous belt
  • drying diminish foaming properties
  • addition of sugar improve retention of flavour.
freezing
Freezing
  • Albumen - no concerns
  • yolk addition of 10% sugar or salt needed to prevent gelation