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PROTEIN (Properties Of Protein (Gel Formation (Gelatine Is Made From The…
PROTEIN
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Chemical Structure
Each Amino Acid Is Made Up Of C, H, COOH, NH2 And A Variable, Which Changes With Each Amino Acid
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The Chemical Structure Of A Basic Amino Acid: 
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R -> Variable, Which Is Different In Each Amino Acid
For Example, When R is Hydrogen -> Glycine Is The Amino Acid
Peptide Links
A Peptide Link Is Formed When Two Amino Acids Join Together. The Acidic Group Of One Amino Acid (COOH) Reacts With The Alkali Group (NH2) Of The Other, With The Elimination Of A Water Molecule. This Process Is Called Condensation. The Reverse Of This Process, Which Occurs During Digestion, Is Called HYDROLYSIS (Addition Of A Water Molecule). This Results In The Peptide Link Being Broken. The New Molecule Is Called A Dipeptide.
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Properties Of Protein
Solubility
Most Proteins Are Insoluble In Water, Except Albumin (Egg White) In Cold Water And Collagen In Hot Water
Elasticity
Gluten, A Fibrous Protein In Wheat, Is Quite Elastic, Which Allows Bread To Rise When Heat Is Applied.
Denaturation
Denaturation Is A Change In The Nature Of The Protein Chain.
It Causes Protein Chain To Unfold, Which Leads To An Irreversible Loss Of Structure, e.g. A Boiled Egg
Denaturation Is Caused By Heat, Agitation And Chemicals.
1.Heat: Causes The Protein To Coagulate (Harder) And Set, e.g. Eggs
2.Agitation (mechanical action): Whipping A Protein Food Can Cause Partial Coagulation, e.g. Whipping An Egg White Turns It Into Foam
3.Chemicals: Acids, Alkalis And Enzymes Also Cause A Change In The Protein Structure, e.g. Lemon Juice, An Acid, Added To Albumin, Which Is Present In Eggs, Causes It To Curdle.
Maillard Reaction
The Non-Enzymic Browning Of Protein Foods: An Amino Acid Reacts With Sugar, A Carbohydrate, Under Dry Heat Conditions, e.g. Roast Potatoes
Moist Heat (Stewing, Boiling, Steaming)
These Methods Cause The Connective Tissue Of Meat To Change To Gelatine, Which Makes It More Digestible
Gel Formation
Gelatine Is Made From The Protein Collagen; It Can Absorb Large Amounts Of Water To Form A Gel. If This Is Heated, It Liquefies And Forms A Sol
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A Gel Is A Semi-Solid Viscous Solution With A Three-Dimensional Network In Which Water Molecules Can Become Trapped
This Setting Power Is Used In The Preparation Of Cheesecakes, Jellies And Soufflés.
Foam Formation
When Egg White Is Whisked, The Protein Structure Unfolds And Air Bubbles Form Around It
The Air Bubbles Entrap Air, Thus Creating Foam
The Whisking Also Produces A Small Amount Of Heat, Which Sets The Egg White Slightly. However, It Will Collapse After A Time Unless Heat Is Applied, e.g. Meringues
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Digestion Of Protein
During Digestion The Protein Chains Are Hydrolysed, i.e. For Each Peptide Link, One Water Molecule Is Added And Broken Down Into Amino Acids With The Help Of Protein-Slitting Enzymes.
See 2010, HL, Section A, 1
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