Once relatively unknown to most people, collagen has attracted plenty of attention in recent years thanks to its perceived anti-ageing properties.
Now, collagen is the ultimate buzzword in skincare and nutrition.
Since collagen is big news at the moment, and it can be found within a number of supplements, due to the number of important roles that it plays within the body.
Most of us are aware of the role that collagen plays in our skin, but did you know that collagen is responsible for much more than that?
While it’s been called the ‘holy grail of skin health’, it’s also thought to help protect against joint stiffness.1,2
It comes as no surprise that people are turning to collagen supplements, such as fish scale collagen, fish collagen powder or fish collagen peptide, in an attempt to improve the appearance of their skin.
So if you’re considering trying it for yourself, you’re in the right place as this guide focuses on all the different types of collagen out there.
In this article, we’ll run through:
What is collagen?
Let’s start with the basics. What actually is collagen?
The most abundant protein in the body, collagen is the main component of our bone, skin, muscle and ligament structure.3
As it’s found in most tissues, collagen can be found in other areas, including tendons, gums and eyes.
Its fibrous properties mean collagen adds structure, strength and resilience to both hard and soft tissues.
Good amounts of collagen in the skin are also essential for skin elasticity and plumpness.4,5
What does collagen do?
The bodies of all animals, including humans, contain large amounts of the protein, collagen.
Collagen is what adds structure and strength to our skin, organs, bones, tendons and ligaments.
Collagen - which contains the three amino acids glycine, proline and hydroxyproline - plays such an important role in the body that it reportedly makes up 75% of the skin’s support structure.6
In terms of what this structure is and collagen’s role in it all, think of your skin as being a mattress.
Collagen is the frame that’s around your mattress, and gives it the necessary support, shape and structure.
How is collagen formed?
The body makes its own collagen, in a process known as collagen synthesis.
To do this, the body needs a variety of amino acids, mainly glycine, proline and hydroxyproline.7
We get these amino acids from protein in the food we eat.
When we eat protein, that protein is broken up into amino acids during digestion.
These amino acids then bind together densely in a tough, rope-like chain to create collagen.
What happens to collagen as we age?
Collagen makes up eighty percent of human skin, and works together with the protein elastic, to keep our skin elastic and taut.
However, the body’s ability to synthesise collagen declines gradually as we get older.
Unfortunately, this means that the older we get, the more our collagen levels start to drop. As every year goes by, our bodies produce less and less collagen.
It also makes lower quality collagen too. What’s more, free radicals, such as the sun’s UV rays, pollution and smoking, can speed up the rate at which our collagen levels deplete.8,9
Considering that just about everyone would like to retain the smooth, dewy skin of youth for as long as possible, it’s easy to see why collagen is such a hot ingredient within the health and beauty industries.
As our bodies age, natural collagen production slows, leading to wrinkles and lines.
Skin with less collagen is drier, and this effect is amplified by factors including sun exposure, cigarette smoke, and pollution.10
What are collagen peptides?
Collagen peptides (also known as hydrolysed collagen) are not quite the same as the collagen that occurs naturally in the body.
While collagen is the long chain of amino acids that makes up skin and connective tissue, collagen peptides are derived from that collagen and are formed of much shorter chains of amino acids.11
Some small studies have shown that collagen peptides improve certain properties of the skin conditions such as skin moisture, elasticity, wrinkles, and roughness, and collagen has also been shown to increase skin hydration.12,13
Where does collagen in supplements come from?
To add collagen to a supplement, it is generally derived from either bovine or marine sources.
These are both effective forms, but need to be good quality, so look out for grass-fed or pasture-raised types.
Fish collagen proteins are usually found in the skin and scales and are a source of type I and type II collagen.
Bovine collagen comes from the bones and hides of cows and is a source of type I and type III collagen.
The smell and taste of both is barely discernible within a supplement, so it can easily be taken on its own or mixed into drinks, smoothies and food.
Collagen is a protein that makes up a large part of our bodies – the skin, organs, bones, tendons and ligaments. It contains the three amino acids glycine, proline and hydroxyproline.
The main benefits of collagen
Below, are the top benefits of collagen...
It can help prevent premature ageing of the skin
It’s thought that in young skin, collagen fibres are firmly tethered to skin cells, which is what creates that firmness.
Over time, this bond degrades. Therefore, in older skin, less of the cell surface remains attached to collagen fibres below.14
This accounts for the sagging and lack of structure in much older skin.
Other factors affect the body’s production of collagen, too.
Smoking, environmental pollution, a high-sugar diet and the effects of ultraviolet (UV) light all contribute to premature ageing of the skin, also known as photoaging.
In older skin, the collagen-producing cells ‘exhibit less replicative capability’ – meaning they don’t renew themselves as rapidly or as effectively as in younger skin.15
Taking collagen supplements might help improve the appearance of your skin and reduce visible hallmarks of ageing.
A study from 2015 found that after 8 weeks of taking an oral collagen peptide supplement, significant improvements were found in both the hydration and collagen density of the participants’ skin.16
It could help maintain joint health as we age
It’s not just your skin which relies on collagen to look youthful. Collagen helps keep your body feeling young, too.
Joints are protected by a tough, rubbery cartilage which stops the bones in joints from grinding together.
The gradual drop in natural collagen levels in the body can lead to loss of cartilage and joint discomfort pain, stiffness and decreased flexibility over time.
It is thought that this link between taking collagen orally and healthy joints pain is due to the additional collagen accruing in cartilage and stimulating the body to produce more collagen in the problem areas.17
There have been studies to back this up too, which indicate that ingesting hydrolysed collagen stimulates the regeneration of collagen tissues, reducing joint discomfort and helping to prevent bone density loss.18
It can help heal the gut
Collagen gives structure to all of the body’s tissues, including the lining of the stomach and intestines.
Therefore, collagen can help the body repair damaged cells in these areas.19
Want to find out more about the different benefits of collagen? Check out our guide to the top 9 benefits of collagen while you’re here.
What are the different types of collagen?
We tend to think about collagen as a single entity.
However, there are in fact actually 28 different types of collagen!20
But there are three main ones that we tend to concern ourselves with most.
Many of these types of collagen come from healthy proteins and you can add them to your diet by consuming cartilage directly from the body, boned fish and organ meats.
As this is not a typical diet for the majority of people, a collagen supplement is proving to be a popular alternative.
These are three main types of collagen:
- type I is the most common type of collagen – found in skin, bone, teeth, tendon, ligaments, vascular ligature, and organs21
- type II is mainly found in cartilage22
- type III is present in the skin, muscle, and blood vessels 23
Collagen Type 1
The majority of the body’s collagen is type I.
As much of 90% of your collagen is type I and it is made of very densely packed fibres.24
As we touched on before, it is this type of collagen that provides structure to so many different elements of the body, including the skin, bones, tendons, cartilage, connective tissue and teeth.
This is the type of collagen that you have probably heard of when it comes skin, hair and nail health, and the natural levels of type I collagen found in the body starts to decline in our twenties.
Due to its prevalence in connective tissue, its decline may result in less firm skin, brittle nails, thinning hair and fine lines and wrinkles.
The fact that it is such a huge part of the tendons, organs and bones makes it essential in remaining active as you age.
Any collagen peptides that you might take are primarily composed of type I collagen.
Collagen Type 2
Collagen type II takes the form of more loosely packed fibres which tend to be found in elastic cartilage.25
This cushions your joints, supporting movement and function and is often found within supplements in order to help to support the skeletal system.26
This type of collagen is made up of long identical chains of amino acids forming a tight network of fibres.
It gives cartilage its strength and elasticity, which is vital when it comes to allowing tissue to bear mechanical stress and shock absorption.
Therefore, adding type II collagen to your body can help to deal with the wear and tear that we all put our joints through.
Collagen Type 3
Collagen type III supports the structure of the muscles, organs and arteries within the body.27
It is the second most abundant collagen type and is generally found in reticular fibres such as the bone marrow.
Other types of collagen
Collagen type IV is found in the layers of your skin. It forms in a sheet and is the main collagen component of the basement membrane.
Different sources of collagen
Thereafter, collagen can come from several sources.
Collagen from different sources holds different properties and is found in different parts of the body.
- Marine collagen is extracted from the bones, skin and scales of fish. This is thought to be the most effective at skin and bone support.
- Bovine collagen comes from cows and is thought to help with joint health.
- Vegetarian/Vegan collagen is not ‘true’ collagen as it comes from non-animal sources. However, it is still thought to help stimulate the natural collagen synthesis process.
- Hydrolysed collagen refers to collagen that has been broken down into smaller molecules to make it more easily absorbed into the bloodstream.28
- Gelatin isn’t strictly collagen, although the two are similar. Gelatin has been used in food, medicine and cosmetics for decades and is a collagen derivative that is extracted from the bones of animals, usually by boiling. Humans can’t directly absorb collagen extracted this way.29
What is marine collagen?
Marine collagen is a type of collagen protein sourced from fish and other sea life, such as jellyfish.
It’s a growing market, with public demand increasing following a series of successful studies into its effectiveness.30,31
Marine collagen is renowned for its high collagen content. It’s also absorbed well by the body and is considered as being more eco-friendly and sustainable than other collagen sources.32
How is marine collagen created?
Marine collagen is derived from the skin, bones and scales of fish.
After the flesh of the fish is removed for food, the fish viscera (that’s everything that’s left) is cleaned and the collagen is extracted.33
What is hydrolysed marine collagen?
Sometimes, the collagen is then hydrolysed, which means the long, rope-like chains are broken down into shorter chains, which are easier for us to absorb through our gut and into our bloodstream.34
Hydrolysation can be done chemically, using acids, or by physical methods, such as heating.
What’s left is a concentrated collagen that’s sold in the form of marine collagen powder or added to drinks, tablets, or even, coffee whitener.
Why take marine collagen?
The body has a remarkable ability to produce its own collagen – the protein that gives skin its bounce, elasticity and plumpness.
However, collagen synthesis (the process of combining different amino acids and components to make new collagen) declines as we age. Which is where marine collagen comes in.
What does marine collagen do?
Marine collagen is classified as being a type I collagen.
Type I collagen is the most abundant form of collagen in the body and is found in tendons, ligaments, skin, bones, teeth, hair and nails.
Marine collagen helps the skin repair itself.35
The trauma to the healthy tissues causes the growth of thick, fibrous tissues at the wound site, commonly known as scar tissue.
Marine collagen is thought to give your natural collagen production support by triggering your body to ramp up its collagen synthesis.
In 2016, researchers in Russia conducted a study that found that after 8 weeks of marine collagen supplementation, skin elasticity, sebum production and skin thickness and density were ‘remarkably improved’.36
Marine collagen is a type of collagen protein that’s sourced from fish and other sea life, such as jellyfish.
9 marine collagen benefits
Below are the top benefits of marine collagen...
Supports skin health
Collagen is what holds our skin tissue together.
As we age, the amount of collagen our body naturally produces decreases, meaning that older skin is not as firm or hydrated as younger skin.37
Research carried out on animals has found that marine collagen maintains dermal thickness on mice by promoting the number and activity of skin fibroblasts, or cells in the dermis that produce collagen.38
Meanwhile, in another study, women who took a supplement that contained hydrolysed type I collagen had better supported skin with diminished appearance of lines, photo-aging, and better maintained moisture levels.39
Improves sleep quality
The amino acid, glycine, which is found in marine collagen, has been linked to having a positive impact on sleep quality.
A review of research found that having glycine before bed helps maintain satisfactory levels of self-perceived sleep quality.40
Glycine is also believed to help maintain our core body temperature, which can help with getting a better night’s sleep.41
Marine collagen is kind to the gut because it’s easy to digest.
What’s more, its amino acid make-up, which includes glycine and glutamine, may support the tissue that lines the digestive tract.42
Glycine has been connected with helping with inflammation, and glutamine is necessary for the health of the enterocytes, or epithelial cells, that line the gastrointestinal tract.43
Provides workout support
Collagen is essentially a concentrated source of glycine, which helps the body produce creatine, and can help support muscle mass and exercise performance.44,45,46
Marine collagen also contains proline, which acts as an antioxidant and helps monitor cell damage that may cause post-workout achiness.47
Some studies have found that collagen supplements such as salmon collagen or fish skin collagen, in particular, may help to support muscle mass.48
According to one animal study, marine collagen enables the body to absorb calcium, phosphorus and other minerals.49
This is due to its close connection with osteoblasts, the cells in our bones that synthesise and mineralise bones.
Osteoblasts secrete collagen, creating the unmineralised portion of the bone called the osteoid.50
Stronger nails and hair
It’s believed that taking collagen may lead to increased hair and nail growth.
However, studies are limited, especially in relation to bovine and porcine-sourced collagen.
According to one 24-week study, people who took bioactive collagen peptides reported a 12% increase in nail growth rate and a 42% decrease in the frequency of broken nails.51
Marine collagen reportedly gets to work more rapidly than bovine collagen.
This is because the molecules in type I collagen enable it to be broken into smaller pieces than other types.
Because most marine collagen products contain only type I, they’re believed to absorb into your bloodstream faster than bovine collagen, which contains collagen types I and III.52
Sustainable source of collagen
Most forms of marine collagen come from fish waste that, if it wasn’t used for marine collagen, would otherwise be discarded as a by-product of the fishing industry.
In turn, this makes marine collagen the most sustainable, eco-friendly source of collagen there is, as it’s essentially made from something that would otherwise be surplus to requirements.
Collagen supplements, marine included, may help reduce the risk of heart-related conditions. Collagen provides structure within the arteries.
Without enough collagen, the arteries may become weak and fragile, which may lead to the disease, atherosclerosis.
In one study, 31 healthy adults took 16g of collagen a day for 6 months.
They reported a significant reduction in artery stiffness compared. Their levels of good cholesterol had also increased by an average of 6%.53
Handpicked content: The difference between healthy fats & bad fats
Which is the best fish collagen?
Vitamin C (which is required for normal collagen formation) is included with Holland & Barrett Marine Collagen with Vitamin C.
This type of hydrolysed fish collagen is suitable for pescatarians and might be a good option to encourage collagen formation (as opposed to collagen replacement) since Vitamin C is included alongside the fish collagen.
Fish collagen powder’s benefits include its solubility.
The powdered form can easily be mixed into smoothies or juices, for those who prefer to take their supplements in drinks rather than tablets.
The best collagen for you will depend on your body, so it is worth trying a few different types and comparing their effects.
As studies have shown, it can take up to twelve weeks for any effects to be apparent, so keep at it for a while before switching to a new brand.
Marine collagen is classified as a type I collagen – it’s the most abundant form of collagen in the body and is found in tendons, ligaments, skin, bones, teeth, hair and nails.
Just as there are several benefits to taking bovine collagen, there are several benefits associated with taking marine collagen. These range from skin and gut health to improved bone strength and muscle mass
Fish collagen is one of the best collagen supplements for pescatarians or those who wish to avoid pork and beef-derived products.
Marine collagen comes from fish waste, which might otherwise be discarded as a by-product of the fishing industry, potentially making it the most sustainable, eco-friendly source of collagen.54
Marine collagen is also considered ‘cleaner’ than collagen from land animals, as there is a lower risk of contaminants and no chance of transmissible disease from a fish source.55,56
There are certain cultural and religious factors that could affect the suitability of bovine (cow-derived) or porcine (pig-derived) collagen.
This means marine collagen is the most consumer-friendly type across the world.
As marine collagen is a type I collagen, it’s most suitable for promoting healthy skin and bones, and the best collagen powder for anti-ageing.57
Collagen from bovine and porcine sources is type II collagen – which is found in the cartilage.
Therefore, bovine and porcine collagen is more suitable for people primarily concerned with joint health.
Is fish and marine collagen the same?
Yes, it’s the same thing, but just referred to by a different name. Fish and marine collagen is made from fish waste, hence the name ‘fish collagen.’
And, of course, ‘marine’ has a sea/fish connection too.
Finally, marine collagen is known for being bioavailable – which means we can absorb it into our bloodstream.
This is because it has a low molecular weight and is able to pass through the gut lining.58
Fish and marine collagen are the same thing, which has been linked to minimal side effects.
Marine collagen tends to come from fish waste and potentially contains fewer contaminants and transmissible diseases than collagen that’s made from land animals.
What is bovine collagen?
Another form of collagen supplements is bovine collagen. This means that it could come from any of the following animals:
- Cattle (cows)
Bovine collagen supplements are made by boiling cattle bones or other byproducts in water.
Then when the collagen has been extracted, it is usually dried and powdered to create the tablet or capsule.60
Why take bovine collagen supplements?
When researched, bovine collagen was found to increase collagen type I and III, in contrast to marine collagen which is said to boost types I and II.61,62
Collagen that is found in the skin is generally made up of collagen types I and III, which suggests that this bovine form of collagen could be particularly useful for combatting wrinkles, promoting elasticity, and increasing the level of moisture in the skin.63
Bovine collagen benefits
Below are the top benefits of bovine collagen...
It may help a specific type of arthritis
Osteoarthritis is a specific type of arthritis that disintegrates the cartilage that protects the bones – leading to pain and stiffness in the hands, knees, and hips.64
A study that supports this idea used 30 people with osteoarthritis specifically affecting their knees.
It concluded that participants given 5g of bovine collagen twice a day experienced improvements in their symptoms.65
It may provide similar effects on the skin as marine collagen
One 8-week study in older mice found bovine collagen supplements to significantly improve the skin elasticity, collagen content, collagen fibers, and antioxidant activity.66
Bovine collagen supplements offer a lot of the same benefits as marine collagen.
However, the key differences are that bovine collagen has been around for longer and that it may not be as suitable for certain lifestyle factors or religions.
In addition to this, it may not be as sustainable as marine collagen could be.
What is hydrolysed collagen?
Hydrolysed collagen is collagen that has been extracted from its original source and broken down into smaller molecules to make it easier for us to absorb into our bodies.
This process is known as hydrolysation.67
Before hydrolysation, collagen is typically extracted from bovine (cows), porcine (pig) or marine (fish and sea life) sources.
Once hydrolysed, collagen also takes on antioxidant properties.
This means it might be able to fight free radicals and help prevent cellular damage in the body.68
After undergoing the hydrolysis process, the collagen molecules are also known as ‘collagen peptides’.
How is hydrolysed collagen created/sourced?
In their whole form, collagen molecules are too large to be absorbed by our bodies.
Hydrolysed collagen is broken down in a lab to separate the tough, tightly bound chain of amino acids into smaller strands.
This is done in one of two ways:
- by thermal treatment (heating), followed by the addition of enzymes
- by adding an acid (such as acetic acid) to the collagen 69
Both these methods rearrange the chemical structure of the collagen and result in a lower molecular weight, which allows it to pass through gut lining and be absorbed into the body.70
Hydrolysed collagen is then available as collagen pills, collagen powder and various types of collagen drink.
Once the microscopic molecules have been absorbed into the bloodstream, it’s thought that your body’s natural collagen function is triggered, and you begin to synthesise collagen more rapidly.
Why would you opt for hydrolysed vs any other type of collagen?
The appeal of hydrolysed collagen lies in its bioavailability.
It’s more easily absorbed into the body than non-hydrolysed collagen, meaning it’s likely to be more effective and offer more noticeable results.71
Studies on hydrolysed collagen supplementation have been promising for both improving the overall appearance of skin and for improving joint health.
Studies confirm that hydrolysed collagen that is taken orally (such as in a powder or capsule form) can then be detected in the bloodstream, meaning that it has been absorbed.72
Taking hydrolysed collagen has been found to improve skin properties such as elasticity and the ability to retain moisture.73
The best collagen supplements
Collagen supplements come in a variety of different forms, so it is important to find one that works for you.
There are powders available that can be mixed into food and drink, or tablets that can be taken daily.
There are also liquids that are taken in small doses each day, on their own or as part of another drink.
You might also like to read more about ‘What is hydrolysed collagen?’
As with any supplement, you should always research what you intend to take and ensure that it meets your own individual needs.
If you have any concerns about your suitability for a collagen supplement, you should consult your doctor or pharmacist first.
What are lycopene and ceramide?
While not technically classed as a type of collagen, both lycopene and ceramide have to be considered when it comes to collagen supplementation – as they may be able to boost the effects.
Much like collagen, lycopene supplementation has been found to be beneficial in reducing oxidative stress markers in menopausal women and has protective effects on bones.74
But it doesn’t end there.
Lycopene is naturally found in the skin, but when exposed to UV rays it is destroyed on a larger scale than originally thought, suggesting that supplementation of this antioxidant in addition to collagen may further combat the signs of aging.75
But what about ceramide? We hear you.
Ceramides make up 50% of the fats that reside in the outer layer of our skin – aka the bit that prevents water loss, protects against UV radiation and maintains your general skin health.76
This is important because studies have shown that ceramides can be distributed into the skin after oral supplementation, which could help to improve skin water loss and the function of the skin barrier.77
So if you can get yourself a supplement that contains collagen in addition to lycopene or ceramide – your skin may very well thank you.
Which foods are a source of collagen?
Although foods don’t contain collagen in a form that we can directly absorb, there are still several foods you can eat to boost your body’s natural collagen.
Remember, your body makes its own collagen, and needs a range of different amino acids to do this.
The best place to get these amino acids is from protein-rich foods, such as lean meat, fish, nuts, seeds, soya products like tofu, beans, legumes and dairy products e.g. cheese, eggs, milk and yoghurt.78
Vitamin C is also used by the body in the process of creating collagen.
So, make sure you pair your protein-rich foods with foods high in vitamin C such as broccoli, leafy vegetables, peppers, chillies, tomato, sweet potatoes or a small glass of orange juice.79
Bone broth has been touted as a way to super-charge your body’s collagen levels.
Bone broth is essentially a soup or stock made from boiling animal bones and simmering them for long periods of time – up to three days or more!
This process releases collagen from the bones and connective tissues, as well as vitamins and minerals.
However, although bone broth does contain collagen, it is processed by the body like any other protein, that is, it breaks it down into amino acids, from which the body builds its own collagen.80
Thanks to an upsurge in demand from the health and beauty industry, the collagen market has grown exponentially in the past decade.81
You can now buy:
- Collagen tablets
- Collagen capsules
- Liquid collagen drinks
- Collagen powder
- Collagen creams
- Collagen serums
- Collagen coffee creamers
- Collagen gummies
- Collagen peptides
- Effervescent collagen
- Collagen sachets
- And even, collagen chocolate!
As there are different types of collagen, dosage recommendations vary from product to product.
Possible collagen side effects
Collagen is considered very safe thanks to its biocompatibility with the human body.
Essentially, as it exists in our bodies naturally, it’s very well-tolerated and no major side effects have been reported.
Some people have reported minor gastrointestinal discomfort, such as mild diarrhoea, a feeling of heaviness in the stomach or rashes while taking collagen.82
But other than this, these are the main side effects to be aware of:
High calcium levels
According to the US National Library of Medicine, taking collagen supplements alongside calcium supplements may lead to high calcium levels or hypercalcemia.
Collagen supplements that come from marine sources, such as shark cartilage or shellfish, may contain high levels of calcium.83
High calcium levels can lead to constipation, bone pain, fatigue, vomiting and nausea.
It’s therefore not advisable to take marine collagen if you already have high calcium levels or alongside calcium supplements.84
Always speak to your GP first before taking any type of supplement to make sure it’s safe for you to do so.
Some people, especially if they have a fish allergy, may find they are allergic to marine supplements that have been made from shellfish or other marine sources.
According to a study published in Allergology International, fish collagen caused an allergic reaction in a 30-year old woman with a known marine allergy, even when the supplement was produced using high-heat methods.85
If you are allergic to shellfish or have another type of marine allergy, avoid taking marine collagen supplements.
Doing so could lead to side effects, such as swelling of the lips, face, tongue and throat or other parts of the body; wheezing, nasal congestion or trouble breathing; abdominal pain, diarrhoea, nausea or vomiting.86
According to the US National Library of Medicine, some collagen supplements can leave a bad taste in the mouth.87
Both marine and bovine collagen supplements reportedly don’t taste or smell very pleasant.
The final say
The key different types of collagen are known as types I, II and III.
But supplements get their collagen sources from marine creatures, bovine animals and some may even come in the form of hydrolysed collagen (or collagen peptides).
While collagen supplements may be able to offer a lot of benefits, it’s important to speak to your GP before trying them to ensure they’re the right choice for you.
The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.
Last updated: 2 December 2021
- The Science and Technology of Gelatin. Academic Press Inc.; London, UK: 1977. pp. 73–108.
- Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates. Iwai K, Hasegawa T, Taguchi Y, Morimatsu F, Sato K, Nakamura Y, Higashi A, Kido Y, Nakabo Y, Ohtsuki K. J Agric Food Chem. 2005 Aug 10; 53(16):6531-6.