Proteins and food
When cooking or preparing meats, different temperatures must be used depending on how much protein is found in the tissue.
Tender, lean meats such as fillet steak must be cooked at lower temperatures to retain their texture. This is because the protein molecules in the meat will chemically change when exposed to heat.
While proteins are long, spiral molecule chains, there are two main types of protein molecules.
Fibrous proteins
These molecules are the major structural material of animal tissue and are found in animal hair, nails and muscle.
Fibrous proteins have their long, spiral chains folded to form long, thin shapes. They are strong and are generally insoluble in water.
Globular proteins
Globular proteins are molecules involved in the regulation of life processes. For example, haemoglobin, and certain hormones like insulin and enzymes are all examples of globular proteins.
They have their spiral chains folded intro spherical shapes and are generally soluble in water.
However the protein chains are arranged, they are held in these shapes by intermolecular bonding between the side chains of the amino acids involved.
During cooking, when the proteins are heated, the molecules become agitated and move around causing the intermolecular bonds between molecules to be broken.
This allows the protein to denature (change shape) which changes the texture of foods. This explains the difference in structure between a raw egg and a fried egg.