Functions of Protein in Food

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Functions of Protein in Food

• Structure
• muscle fibers (meat)
• texture (water holding capacity (salt))
• gels (collagen ? gelatin)
• stabilize foams (whipped cream)
• network formation in breads and
• cakes
• Enzymes
• catalyze reactions
• Emulsification
• hot dogs, salami, pepperoni, etc.

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Proteins of Animal Origin

• Meat, fish, and poultry
• soluble- enzymes, actin, myosin
• insoluble- connective tissue
• (muscle- 18-20 protein)
• Milk
• caseins (80 of total)
• lactoglobulin
• immunoglobulin
• Eggs
• yolk- 33 protein, 67 lipid
• white- 12 protein

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Proteins of Plant Origin
Vegetable- generally not a good source of
protein Cereal- mainly found in the endosperm as
opposed to the germ and bran wheat barley
rye oats corn rice
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Major Cereal Proteins

• Wheat Endosperm
• Gluten (11 mixture of gliadin and glutenin),
  used for flour doughs because of elastic and
  cohesive properties (80-85 )
• Albumins and globulins- they coagulate and used
  to make foams (15- 20 )

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Major Cereal Proteins

• Corn Proteins
• 40-50 zein
• 20-30 glutelin
• Rice Proteins
• high in glutelins
• low in lysine
• Seed Proteins (mostly globulins)
• Legums- soybeans, peanuts, peas, beans (20-50
  protein)
• Oilseeds- sunflower, sesame, cotton seed (20-30
  protein)

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Soybean Contaminants
Trypsin inhibitor- prevents proteolysis Hemagglut
ins- causes red blood cells to agglutinate Saponi
ns- glucosides (surfactants) Estrogens-
hormone Goitrogens- cause goiters
(Proper heat treatment required to destroy)
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Typical Scheme for Protein Isolation

• homogenization
• grinding
• sonication
• osmotic pressure

e.g., protamine sulfate
e.g., ammonium sulfate

• gel filtration
• ion-exchange
• affinity

• PAGE
• native
• SDS

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Ammonium Sulfate Fractionation

• Increasing the salt concentration will cause
  proteins to precipitate out of solution (i.e.,
  salting out).
• Different proteins are soluble at different salt
  concentrations (i.e., basis for fractionation).

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Gel Filtration Chromatography
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Elution Profile after Gel Filtration
Chromatography
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Molecular Weight Determination by Gel Filtration
Chromatography
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Ion-Exchange Chromatography
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Elution of Protein with Salt from an Ion-Exchange
Column
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Affinity Chromatography Based on an Antigen Ligand
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Affinity Chromatography Based on an Antibody
Ligand
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Polyacrylamide Gel with Tunnels for Separation
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Treatment of Protein with Sodium Dodecyl Sulfate
Proteins is a negatively charged rod
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SDS-polyacrylamide Gel Electrophoresis
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SDS-Polyacrylamide Gel Electrophoresis Analysis