Collagen peptides and gelatin: how do they differ?

Gelatin and collagen peptides are both made from collagen, the protein in animal skin, bone and connective tissue. The difference is how far the collagen has been broken down. Gelatin is collagen partly broken down by pre-treatment and extraction in hot water, and it sets into a gel when it cools. Collagen peptides, also called hydrolysed collagen, are cut much further, usually with enzymes, into short chains of about 3 to 6 kDa; they dissolve easily and stay thin even at high concentrations. Most of the world's gelatin is made from pig skin and from cattle hides and bones, and only a small share from fish.

This article compares the two by how they are made, their size, their physical properties and their raw materials, using reviews and laboratory studies, including several from Thai universities. It does not discuss what they do in the body. For how the body digests collagen, see What happens to collagen you eat?, and for collagen by animal source, see What kinds of collagen are there, and how do they differ?

What are gelatin and collagen peptides made from?

Both start from collagen, which is built from three long protein chains twisted around each other in a triple helix.

Collagen, the starting material

A 2021 review in Marine Drugs by Al-Nimry and colleagues describes collagen as a large protein of three strands, with a molecular weight of around 350 kDa, each strand around 105 kDa and 300 nm long. About 33% of its amino acids are glycine and 22% proline, and it also contains hydroxyproline and hydroxylysine, arranged in a repeating sequence. A 2019 review in Molecules by León-López and colleagues gives a slightly different figure for the whole molecule, 285 to 300 kDa, with each alpha chain of about 1,014 amino acids and around 100 kDa. The exact number depends on the source and method, but both reviews describe a very large molecule.

Three forms side by side

How is gelatin made?

Al-Nimry and colleagues describe gelatin as the product of partial hydrolysis of collagen, with incomplete breakage of the cross-links that hold the collagen molecule together.

Three main steps

1. Pre-treatment: the raw material is washed and treated with acid, alkali or an enzyme such as pepsin.
2. Extraction: the material is heated in water, which is the actual extraction of gelatin.
3. Finishing: the gelatin is filtered, dried and ground into powder, which can also be made into sheets.

Type A and type B gelatin

The pre-treatment depends on the raw material. Al-Nimry and colleagues explain that acid treatment suits the skin of pigs and fish, whose collagen has fewer cross-links, while alkaline treatment suits cattle hides, whose collagen is more cross-linked and more complex. This gives two types of gelatin.

A 2022 review in Polymers by Lu and colleagues uses the same split.

Extraction temperature and time change the gelatin

Thai studies show how much the extraction step matters. In a 2014 study from Prince of Songkla University, gelatin from seabass skin extracted at 45 °C for 3 hours had the highest gel strength (369 g), and gel strength generally fell as the extraction temperature and time increased. Yield, on the other hand, was higher at 55 °C (62.0% to 66.4% on a dry weight basis) than at 45 °C (51.6% to 57.3%).

How are collagen peptides made?

Collagen peptides go a step further than gelatin: the chains are cut into short pieces.

Unfolding and cutting the chains

León-López and colleagues explain that heating collagen above 40 °C makes the triple helix come apart into three randomly coiled alpha chains. Protein-cutting enzymes such as alcalase, papain or pepsin then break the chains into small peptides of about 3 to 6 kDa. Chemical hydrolysis in acid (acetic, hydrochloric or phosphoric acid) or alkali is another route, but the review notes that these methods are strongly corrosive and leave a high salt content after neutralisation. Other methods use high temperature and pressure, such as subcritical water between 100 and 374 °C at less than 22 MPa.

The degree of hydrolysis

How far the chains are cut is called the degree of hydrolysis. The review notes that the properties of collagen peptides, including how well they dissolve, depend on the type and degree of hydrolysis and on the enzyme used. It gives an example for pig skin: peptides made by a hydrothermal process were around 1 to 10 kDa, and treatment at 150 to 250 °C and 350 to 3,900 kPa gave peptides smaller than 15 kDa.

Why does gelatin set into a gel?

Gelatin is a thermo-reversible gel: Al-Nimry and colleagues explain that it turns liquid when heated and forms a gel when cooled. The 2021 study by Lueyot and colleagues describes the gel as a network of unfolded collagen coils held together by hydrogen bonds.

Gel strength, or bloom

Gelatin is graded by gel strength, often called bloom. In the 2021 study by Lueyot and colleagues at King Mongkut's University of Technology North Bangkok, a 6.67% gelatin gel was made according to the method of the Gelatin Manufacturers Institute of America, kept at 4 °C for 18 hours and then measured with a texture analyser. The result is given in grams. A review by Boran and Regenstein notes that gelatin quality is judged industrially by gel strength, viscosity, melting or gelling temperature, water content and microbiological safety.

Collagen peptides behave differently

León-López and colleagues report that collagen peptides are highly soluble in water and have very low viscosity whatever the concentration, because the chain segments are so small. They cannot form a film on their own and have to be combined with other materials to do so.

Melting and gelling temperatures

Gelatin melts at a temperature that depends on its raw material. Boran and Regenstein note that both the melting and gelling temperatures of gelatin are below human body temperature.

Al-Nimry and colleagues note a practical consequence: warm-water fish gelatin melts more easily in the mouth, and products made from it need to be kept cool, while products made from mammalian gelatin can be kept at room temperature.

What raw materials are used, and how do they differ?

Where the world's gelatin comes from

Shares as reported by Al-Nimry and colleagues (2021). Lueyot and colleagues put the world's use of gelatin at some 450 kilotons in 2018, for gelling, stabilising, emulsifying and binding water in food, pharmaceutical and cosmetic products.

Fish and mammals differ in amino acids

Al-Nimry and colleagues report that collagen and gelatin from fish contain less proline and hydroxyproline and more threonine and serine than those from pigs and cattle. Gelatin from cold-water fish has even less hydroxyproline, which gives it lower gel strength and lower melting and gelling temperatures. The 2014 seabass study found an imino acid content (proline plus hydroxyproline) of 198 to 202 per 1,000 amino acids, and the 2016 goat skin study 226 per 1,000.

No gelatin from plants

Lu and colleagues state that gelatin can be extracted from animal collagen but not from plants, and that so-called vegetable gelatins, such as seaweed gels, are not classified as gelatin because they have no chemical relationship with it.

Religious diets

Al-Nimry and colleagues note that Muslims and Jews do not eat pig products and Hindus do not eat cattle products, which is one reason for interest in fish gelatin.

What have Thai researchers found about gelatin from local animals?

Fish skin and other by-products from Thai seafood and meat processing have been studied as gelatin sources. All of the studies below were laboratory studies of the gelatin itself; none studied people.

Why the numbers cannot be compared directly

Each study used its own extraction conditions and measuring method. Lueyot and colleagues point out that their gel strength values were higher than in other reports partly because they calculated the 6.67% concentration based on moisture content. Values from different studies therefore show differences between raw materials within a study, not a ranking across studies.

Where do gelatin and collagen appear in everyday food?

Which foods use gelatin?

Al-Nimry and colleagues list uses of gelatin as a stabiliser and texture enhancer in dairy and bakery products and in desserts such as gummy candies and marshmallows, and note that the pharmaceutical industry also uses it. Lu and colleagues describe its use in edible films and coatings.

Gelatin from home cooking

The Nutrition Source at the Harvard T.H. Chan School of Public Health says gelatin is a form of collagen made by boiling animal bones, cartilage and skin for several hours and letting the liquid cool and set. It adds that collagen is found in tough cuts of meat full of connective tissue and in the bones and skin of freshwater and saltwater fish, and that bone broth is made by simmering animal bones in water with a little vinegar for 4 to 24 hours.

Do they count as protein?

Collagen, gelatin and collagen peptides are all protein. There is no Thai Reference Daily Intake (Thai RDI) for collagen or gelatin; the Thai RDI covers total protein from all foods, at 50 g a day. About 33% of the amino acids in collagen are glycine and 22% proline (Al-Nimry et al. 2021). For the amino acids the body needs from food, see What are essential amino acids?

What should people keep in mind about gelatin and collagen peptides?

Fish allergy

Gelatin and collagen peptides may be made from fish skin and scales. The US FDA lists fish among the major food allergens. People with a fish allergy should talk to a doctor or pharmacist.

Pregnancy and regular medication

If you are pregnant or breastfeeding, or take medication regularly, talk to a doctor or pharmacist before taking dietary supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.