Native collagen is a scleroprotein based on a polypeptide chain comprising approximately 1,050 amino acids. Three of these chains form a triple helix.
Superimposition of many of these triple helices produces fibrils of collagen that are stabilized by cross-linking, hence forming a 3-dimensional network structure. This particular structure renders collagen insoluble; it is then brought into soluble form by partial hydrolysis as gelatine or gelatine hydrolysate.
The amino acid content of collagen and hence of gelatine is about one third glycine and a further 22% proline and hydroxyproline; the remaining 45% comprise 17 amino acids. Gelatine has a particularly high content of acidic and basic amino acids. Of the acidic amino acids (glutamic acid and aspartic acid), about 1/3 is present in the amido form as glutamine and aspargine. Cystein is completely absent; of the sulphur-containing amino acids, methionine is the only one present, in low proportion.
Commercially available edible gelatines have the following composition:
• 84 - 90% protein
• 8 - 12% water
• 2 - 4% mineral salts
They contain no fat or carbohydrates, no purine or cholesterol and are in addition free of all preservatives. All edible gelatines comply fully with all bacteriological standards.