What's the difference between collagen and gelatin -- and collagen hydrolysate?

The Collagen Molecule

In humans, collagen comprises one-third of the total protein, accounts for three-quarters of the dry weight of skin, and is the most prevalent component of the extracellular matrix (ECM). Twenty-eight different types of collagen composed of at least 46 distinct polypeptide chains have been identified in vertebrates, and many other proteins contain collagenous domains 

The collagen molecule consists of 3 polypeptide chains. The three helical subunits are wound together to create a triple helix. This tightly wound molecule is the most abundant protein in the human body. The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline.

Collagen is special because it contains an abundance of three precious amino acids that you won’t find in meaningful amounts in many other foods:

• Glycine
• Proline
• Hydroxyproline

These three amino acids are the keys to collagen’s anti-aging and flexibility-boosting benefits.

The tight packing of PPII type (polyproline II) helices within the triple helix mandates that every third residue be Gly, resulting in a repeating XaaYaaGly sequence, where Xaa and Yaa can be any amino acid. This repeat occurs in all types of collagen, although it is disrupted at certain locations within the triple-helical domain of nonfibrillar collagens. The amino acids in the Xaa and Yaa positions of collagen are often (2S)-proline (Pro, 28%) and (2S,4R)-4-hydroxyproline (Hyp, 38%), respectively. ProHypGly is the most common triplet (10.5%) in collagen.

Note that although the three polypeptide chains in the triple helix of each collagen type can be identical as the case of the pdb file used on this page pdb: 1CGD, heterotrimeric triple helices are more prevalent than are homotrimeric triple helices.

Collagen like peptide Jsmol Structure

"The collagen triple helix is a unique protein motif defined by the supercoiling of three polypeptide chains in a polyproline II conformation. It is a major domain of all collagen proteins and is also reported to exist in proteins with host defense function and in several membrane proteins. The triple-helical domain has distinctive properties. Collagen requires a high proportion of the post-translationally modified imino acid 4-hydroxyproline and water to stabilize its conformation and assembly. The crystal structure of a collagen-like peptide determined to 1.85 Angstrum showed that these two features may be related."

The Gelatin Molecule

Gelatin is a mixture of peptides and proteins produced by partial hydrolysis of collagen. Gelatin is a heterogeneous mixture of single or multi-stranded polypeptides, each with extended left-handed proline helix conformations and containing between 50 - 1000 amino acids.

Gelatin can be extracted from the skin, bones, or connective tissues of animals. Gelatin is also known as hydrolyzed collagen, collagen hydrolysate, collagen peptide, gelatin hydrolysate and hydrolyzed gelatin, 

In contrast to collagen, gelatin does not elicit any noticeable antigenicity after implantation. 

Hydrolysis results in the reduction of collagen protein fibrils of about 300,000 Da into smaller peptides. Depending upon the process of hydrolysis, peptides will have broad molecular weight ranges associated with physical and chemical methods of denaturation.

Gelatin is an irreversibly hydrolyzed form of collagen, wherein the hydrolysis reduces protein fibrils into smaller peptides; depending on the physical and chemical methods of denaturation, the molecular weight of the peptides falls within a broad range.

Gelatin is a protein and the only hydrocolloid being a protein. As no other ingredient exhibits as many functionalities as gelatin, it is an unrivalled asset to formulation design.

You can use it for water binding, texturizing and a wide range of other purposes. In fact, gelatin is often used to replace several mono-functional hydrocolloids in a single application.

Collagen Hydrolysate vs. Gelatin

In the hydrolyzed form, the collagen is processed more intensively, which actually breaks up the proteins into smaller pieces. Both have the same amino acids, but different chemical properties.

The amino acid content of hydrolyzed collagen is the same as collagen. Hydrolyzed collagen contains 19 amino acids, predominantly glycine, proline and hydroxyproline, which together represent around 50% of the total amino acid content.

Hydrolyzed collagen contains 8 out of 9 essential amino acids, —two amino-acid precursors necessary for the biosynthesis of creatine. It contains no tryptophan and is deficient in isoleucine, threonine, and methionine.

REFERENCES

1. Brinckmann J. Collagens at a glance. Top. Curr. Chem. 2005;247:1–-6.

2- Matthew D. Shoulders and Ronald T. Raines, Collagen Structure and Stability, Annu Rev Biochem. 2009; 78: 929–958.

3-https://www.rousselot.com/products-solutions/rousselot-gelatin/the-multifunctional-protein/