Protein

Essential Amino acid

Essential Amino acid

Cannot be made by the body and must be taken from the food we eat e.g. valine

Non essential amino acids

Can be made in the body so not essential in our food e.g. Alanine

Sources

Animal; meat(Actin) egg(Albumin) cheese (casein). Plant; wheat(gluten)

Primary protein structure

The sequence or order of amino acids in the polypeptide chains. They are linked by peptide links. Refers to the number of amino acids in each polypeptide chain

Disulphide links

Two sulphur atoms bond

Hydrogen bonds

Hydrogen atom in one chain bonds with an oxygen atom in another chain

Tertiary protein structure

Pattern of folding gives a three dimensional compressed unit, fibrous or globular protein structure

Fibrous proteins

Polypeptide links are straight, coiled, zigzag

Globular proteins

Polypeptide chains are spherical

Denaturation

Change in nature of protein, unfolding of protein chains results in irreversible loss in structure and shape

Heat

Most proteins coagulate when heated e.g. egg whites. Heat causes protein chains to unfold and bond together. Results in hardening/ setting of the protein food

Chemicals

Acid lowers Ph, e.g. lemon juice added to milk causes caseinogen to curdle. The enzyme rennin coagulates milk protein in the stomach

Mechanical action (agitation)

Whisking an egg white cause the protein chain to unfold resulting in partial coagulation, foam forms. Moist heat(boiling) Dry heat(grilling) whisking egg whites (mechanical action)

Elasticity

Proteins like gluten are elastic. Presence of gluten allows bread to rise. Yeast dough is elastic, traps Co2

Solubility

Proteins are generally insoluble in water. Except egg white, soluble in cold water. Collagen, soluble in warm water. Moist heat,stewing

Millard reaction

Non enzymic browning of food when dry heat is applied. Occurs when food is roasted, grilled, baked. Dry heat, a reaction between amino acids and carbohydrates resulting in browning of food, roast beef, potatoes, toast

Gel formation

The protein collagen present in the bones and skin of meet is converted to gelatine on heating. Gelatine has the ability to absorb large amounts of water, when heated, protein chains uncoil and water becomes trapped.

A Sol

A Sol ( a solution with evenly dispersed particles) is formed which on cooling forms a gel

A Gel

a semi solid thickened solution with a 3D network in which water molecules can be trapped. E.g. setting cheesecake

Foam formation

Whisking an egg white causes the protein chain to unfold and air bubbles form, entrap air creating temporary foam. Heat is generated due which coagulates the egg albumin. Egg white slightly sets. Foam will collapse in time unless heated so it sets to form permanent foam. E.g. making meringues

Biological Value

A measure of quantity of a protein in food and determined by the number of essential amino acids present

High Biological Value

Complete protein, contains all essential amino acids required. Generally animal sources apart from soya beans

Low Biological Value

Incomplete protein, lack some essential amino acids. Generally plant sources apart from gelatine

Elements

Carbon (C) Oxygen (O) Nitrogen (N) Hydrogen (H)