Protein properties

Denaturation

Change in the nature of the protein, unfolding of the protein chain(s) results in an irreversible loss in both structure and shape

Maillard reaction

The non enzymic browning of food when dry heat is applied e.g. roast beef, roast potatoes, toast

Physical digestion

The mechanical breakdown of food without the use of chemicals such as enzymes. In the mouth food is chewed to break it down into smaller pieces which will increase the surface area for a quicker rate of chemical digestion

Chemical digestion

The breakdown of food using enzymes. Involves water and enzymes in a process called hydrolysis,

Stomach

Gastric juice, pepsin, proteins, peptones

Pancreas

Pancreatic juice, trypsin, protein, peptones

Small intestine

Intestinal juice, peptidase, peptones, amino acids

Absorption

Amino acids absorbed into blood capillaries in the ileum of the small intestine, ileum has villi which increase the surface area for a faster rate of absorption, amino acids are absorbed by diffusion into the blood capillaries and enter bloodstream, capillaries connect to portal vein which carries the amino acids to the liver

Utilisation

From the liver amino acids will be exported into the bloodstream to replace and repair body cells, form new cells, antibodies, hormones, enzymes, excess amino acids are delaminated in liver to heat and energy

Deamination

Process by which excess protein is used for energy, broken down by the liver, amino group NH2 is converted to ammonia, then to urea, then excreted by the kidneys as a waste product in urine, carboxylate group is oxidised, used to produce heat and energy

Heat ( cause of denaturation )

Most proteins coagulate when heated, heat causes protein chains to unfold and bond together which results in hardening or setting of the protein food

Chemicals ( cause of denaturation )

Acids lowers the pH e.g. lemon juice added to milk causes the milk protein caseinogen to curdle

Mechanical ( cause of denaturation )

Whisking an egg causes the protein chains to unfold resulting in partial coagulation and foam forms

Moist heat ( culinary application of denaturation )

Boiling, converts collagen to gelatine, tenderising meat

Dry heat ( culinary application of denaturation )

Grilling, causes meat to become tougher as the meat fibres shrink and lose water

Whisking egg whites ( culinary application of denaturation )

Mechanical action, used when making meringues

Elasticity

Some proteins such as gluten in flour are very elastic

Culinary application of elasticity

The presence of gluten allows bread to rise during cooking by making yeast dough elastic so it can trap Co2

Solubility

Insoluble in water apart from egg white ( soluble in cold water ) collagen ( soluble in warm water )

Gel formation

Gelatine absorbs large amount of water when heated, as protein chains uncoil and water becomes trapped, a sol is formed which in cooling forms a gel e.g. setting cheesecake and soufflés

Foam formation

Protein chains unfold and air bubbles form which entrap air creating a temporary foam, heat is generated due which coagulates the egg albumin so the egg slightly sets, the foam will collapse in time unless heated so it sets to form a permanent foam e.g. making meringues