What Is Collagen?

Collagen is a fibrous protein found in almost every tissue, including skin, blood vessels, tendons and teeth. It makes up about 30% of all the protein in the body.

It exists as strong, tough fibers between cells and is a main component of the extracellular matrix.

Collagen is especially abundant in skin, tendon and bone.

In skin, type I accounts for 80–90% of collagen and type III for 8–12%.

There are 28 types of collagen, and the main type differs by location.

Type III makes up 30–60% of skin collagen in the fetus and 10–20% in adults.

Collagen has a triple-helix structure made of three chains, with a repeating pattern of the amino acids glycine, proline and hydroxyproline.

The amount of collagen in the body is said to decrease with age. A skin study reported that an index of collagen fiber structure in the cheek dermis declines with age.

In a study of skin cells, type I procollagen produced was 82 ng/ml in people aged 18–29 and 56 ng/ml in those aged 80 and over.

Gelatin is denatured collagen. Breaking gelatin down further with enzymes produces “collagen peptides,” which are used as food ingredients. Collagen has long been used as a raw material for gelatin and glue.

Collagen that is eaten is digested into peptides and amino acids rather than absorbed as is. After oral intake, small peptides such as prolyl-hydroxyproline (Pro-Hyp) increase in the blood.

Japanese women are estimated to take in about 2 g of collagen a day from their regular diet.

In cattle and pigs, collagen is found in bones, cartilage, ligaments, tendons and skin; in fish, in the skin, tendons and swim bladder. Gelatin is also made from collagen.

Collagen used in food and ingredients comes from the bones, cartilage, ligaments, tendons and skin of cattle and pigs, and from the skin, tendons and swim bladder of fish. Its properties differ depending on the animal and body part.

Raw materials

Gelatin is made from pig skin (41%), cattle bone (29.5%), cattle hide (28.5%) and fish (1.5%).

Amino acids

Collagen is rich in proline and hydroxyproline. Their amounts tend to be higher in pig and cattle collagen and lower in fish, especially cold-water fish.

Denaturation temperature

When heated, collagen’s triple helix unwinds (denaturation). The temperature at which this happens differs by source.

Values depend on the measuring method; each table compares values measured the same way within one study.

Structure of fish collagen

Many fish have an extra “α3 chain” in type I collagen that other vertebrates lack. It has fewer heat-stabilizing Gly-Pro-Pro sequences, which is thought to be one reason fish collagen denatures at lower temperatures.

Allergy and raw-material controls

In a study using sera from fish-allergic patients, some reacted to tuna collagen; no cross-reactivity was seen between fish collagen and collagen from other animals. Imports of cattle hide and bone for gelatin and collagen are regulated in relation to BSE.

Type I collagen in fish is a major extracellular matrix component widely found in skin, bone, scales and muscle, and has an amino acid sequence similar to that of land vertebrates.

Because collagen is hard to dissolve, it must be processed to extract it. Most collagen in use today is dissolved and extracted by alkali or enzyme treatment.

For fish scale collagen, differences have been reported between collagen extracted with acid and collagen extracted with an enzyme (pepsin).

Dr.JAPAN uses collagen extracted by enzymatic processing from the skin of wild cod caught in the North Atlantic. Its characteristics as a raw material, based on published figures:

Extraction, thermal properties and religious acceptability by collagen source, from published data. Values vary with species and measurement method.

Lower denaturation and melting temperatures mean easier dissolving in cold water and less gelling; mammalian gelatins form stronger gels than cold-water fish gelatin.

Native collagen molecules are very large, with a molecular weight of about 300,000. In cod, the α1 and α2 chains are about 120,000 and 110,000, slightly smaller than in mammals (about 130,000 and 115,000).

Collagen peptides used in foods are made by enzymatically breaking down gelatin, with molecular weights of a few thousand. Peptide size is determined by how far it is broken down (the process), not by the source; a study comparing sources prepared fish, pig and cattle peptides at the same average molecular weight (about 2,000).

Some studies have compared the amount and type of peptides appearing in the blood after taking collagen peptides from different sources.

The peptides appearing in the blood differ by source, but both studies were small and their results differ. They do not show that any source is better for the body.

In a study where fish-skin collagen peptides were taken at 12.5 g a day (five times the usual amount) for eight weeks, no changes were seen in blood test values.