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Sources, isolation and properties of protein ingredients - Gelatins

4 important questions on Sources, isolation and properties of protein ingredients - Gelatins

What is the structure of tropocollagen?

A triple helix formed by 3 peptide chains, each about 110 kDa.

What are the amino acids in tropocollagen proteins?

High content of proline (22%) and glycine (33%). Most of the collagen structure is build-up of repeated sequences of 3 amino acids. Glycine is the first, and then 2 amino acids, of which 1 is often proline.

What is a special property of proline?

It's presence in the amino acid sequence prevents the formation of normal alpha-helices. In collagen, most of the proline residues are present in the hydroxylated form hydroxyproline. Angle between alpha-carboxyl and alpha-amino group is deviated from regular angle due to 5-membered ring. This results in an a-typical angle in the peptide bond. The proline residues are known to interrupt the alpha-helical and beta-sheet structures in globular proteins.

What happens if collagen is heated?

The high temperatures induce loss of the native triple-helical structure. The soluble extracted non-native collagen proteins are called gelatin. After cooling down, the polypeptides will arrange again in (non-native) triple helical structures. The triple helices are also the main reason for the formation of reversible gel structures of gelatin.