By Vicki Johnson – October,
2005
Whether you are interested in cosmetic injection therapies to look younger, or are shopping for top quality leather products, or if you want a nice tender beef steak – you have entered the world of collagen.
In fact, about one quarter of all of the protein in your own body is collagen.
Collagen is a major structural protein, forming molecular cables that strengthen the tendons and vast, resilient sheets that support the skin and internal organs. Bones and teeth are made by adding mineral crystals to collagen. Collagen provides structure to our bodies, protecting and supporting the softer tissues and connecting them with the skeleton. It is incredibly tough stuff.
Facial rejuvenation therapies can include injecting collagen to “plump up” our skin to reduce wrinkles, or to add dimension to our lips. Our skin is made up largely of this simple protein, collagen.
Leather (an 8.9 billion dollar per year industry) depends on collagen. In pig skin, for example, collagen fibers are tightly woven from two directions to form a tightly woven meshwork. Collagen is a raw material for major industries in leather, glue and cosmetics.
Agriculture
Research Service (ARS) scientists are working to improve leather tanning
processes with a computer model that offers a three-dimensional view of
collagen--animal skin's fibrous proteins. Collagen is responsible for the
strength and toughness of rawhide and the leather made from it.
While the basic
shape of collagen is understood, it's unclear how these molecules pack into
fine fibers known as fibrils. These molecular reactions determine the strength
and flexibility of collagen fibers.
"Each
collagen fibril is like a very thin, long string," says James M. Chen of
the ARS Eastern
Regional Research Center in Philadelphia. "An enormous number of these are packed together to form skin.”
Collagen is an elongated protein that forms extremely strong but very small fibrils (best seen with an electron microscope). Lots of these collagen fibrils are bound together to form collagen fibers that easily can be seen with a light microscope.
However, collagen is also present in the muscle (meat). When collagen fibers form sheets or cables we can see them in the meat without a microscope, and we may detect them as gristle if they do not gelatinize in cooked meat.
The same collagen that makes our skin, our
tendons and ligaments so strong can also make your steak tough and chewy.
However, if collagen is heated for a long period of time at relatively low temperatures (say around 225 degrees F.) it will breakdown into soft gelatin. Depending on the amount of collagen in a cut of meat the time required to make this conversion can be as much as 15 hours. However most collagen will breakdown if held at the proper temperature in as little as five hours.
Beef carcasses have to be graded by age mainly because of age-related changes in collagen that cause meat from older cattle to be tough. In general, as animals age the amount of connective tissue (collagen) increases. More importantly, the degree of interconnectivity of the collagen increases with age, which results in the collagen becoming resistant to dissolution in cooking. Thus, meat from older animals can become more resistant to tenderization in cooking, and require longer, slower cooking, such as braising, casseroling, or pot roasting to deal with the greater amount and connectivity of the collagen.
A great deal of research has been conducted on ways to improve “beef tenderness”. In the USA, where cattle are fed grains and other supplements to lay down extra fat within the muscle ('marbling'), consumers often choose the most 'marbled' cuts as an indication of tenderness. Yet marbling accounts for a mere 10% of the variation in tenderness. Many lean carcasses that testing has shown were tender have received lower grades because they don't have enough visible fat marbling to be classified as 'USDA choice' or higher. And yet marbling is a very poor predictor of tenderness. Marbling, the visible specks of fat in the lean, is still a factor used in determining the USDA quality grade. However, information in the last decade indicates that marbling exerts only a small influence on tenderness of meat, primarily by acting as a lubricant during chewing.
Certain breeds of cattle that naturally produce leaner beef have been proven to also produce more tender beef when compared to other breeds. The reason for this may well lie in the amount of collagen in the beef.
A recent study conducted by Swiss scientists evaluated the composition and meat quality of six different breeds of cattle, to compare intra-muscular fat (marbling), collagen content and tenderness ratings. A total of 138 steers, an average of 23 per breed, were used in the study. Results are presented in the following table:
|
|
Breed |
|||||
|
Item |
Angus |
Simmental |
Charolais |
Limousin |
Blonde- d’Aquitaine |
Piedmontese |
|
Water, % |
74.9 |
75.0 |
75.3 |
75.2 |
75.2 |
74.5 |
|
Minerals, % |
1.04 |
1.03 |
1.07 |
1.07 |
1.07 |
1.09 |
|
Protein, % |
21.2 |
21.8 |
21.6 |
22.4 |
22.7 |
22.8 |
|
Intramuscular fat (IMF), % |
2.6 |
2.3 |
1.8 |
1.3 |
1.1 |
1.3 |
|
Collagen, mg/100 gm |
559 |
550 |
545 |
495 |
431 |
456 |
|
Shear force, lb |
6.24 |
6.52 |
6.48 |
6.13 |
5.91 |
5.49 |
As shown above, the major differences were in % IMF, collagen (connective tissue), and shear force. As expected, Angus steers had the highest IMF, followed by Simmental and Charolais; Limousin, Blonde, and Piedmontese steers had the least. Interestingly, collagen content followed the same trend as IMF. Piedmontese steers had the lowest shear force. This would be expected because Piedmontese carry the mutated myostatin gene, which results in increased tenderness. Ratings of tenderness by a human sensory panel were in agreement with shear force values (Duffey and Chambaz. 2005. Federal Station for Animal Production Research, Posieux, Switzerland). (Note: Shear Force is a measure of the pounds pressure required to cut through a core of meat; the lower the pounds of force needed, the more tender the meat is.)
This study supports research conducted by the USDA at the Meat Animal Research Center (MARC) which proves that Piedmontese cattle with 1-copy of inactivated myostatin, relative to cattle without inactivated myostatin, will yield about a 7% increase in retail product yield and two copies of mutated myostatin will result in about 20% increase in retail product yield (Wheeler, Shackelford, Casas, Cundiff, & Koohmaraie, 2001). Moreover, meat from cattle carrying inactivated myostatin is more tender in most muscles, especially in muscles in which connective tissue content is the major tenderness determinant (Wheeler et al., 2001).
Dr. Koohmaraie has commented to the North
American Piedmontese Association (NAPA) that the Piedmontese non-functional myostatin
provides a much more dramatic positive effect on beef tenderness than any other
genetic feature he is aware of at this time, largely due to the reduction of
the connective tissue in the meat.
Market trends see the values of round cuts,
chuck cuts, and lean trimmings have decreased 20 and 23, and 31%, respectively,
relative to total carcass value, whereas the values of rib and loin cuts have
increased (Cattle Fax, 1998). The beef industry has made it a priority to
improve the value of these three lower-quality carcass components, which make
up 66% of the carcass. USDA data implies that producing 1-copy Piedmontese +
cattle not only improves the tenderness of the valuable longissimus (loin) but
also could be one method of improving the quality of lower-valued cuts. It
seems likely that many lower-quality muscles would be improved significantly in
1-copy cattle, resulting in substantial
improvement in total carcass value. These results indicate that 2-copy
Piedmontese bulls could be used as terminal sires to produce 1-copy + progeny
with improved tenderness in at least four muscles, resulting in a substantial
increase in carcass value in addition to the previously demonstrated advantage
in yield of saleable product. [T. L. Wheeler, S. D. Shackelford, E. Casas, L. V.
Cundiff, and M. Koohmaraie. Roman L.
Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE 68933-0166]
So, less collagen in beef is desirable, to improve tenderness. But does that mean that these breeds of cattle who naturally contain less connective tissue in their meat, like the Piedmontese, are going to produce poor quality hides for leather ? Surprisingly, the answer is “no”.
The USDA MARC research into the tenderness
of Piedmontese beef also considered this question, and so provided the hides to
the Agriculture Research Service (ARS) to determine if the effects of non-functional myostatin (which
reduces the collagen in Piedmontese beef) would affect the quality of the
leather. The results were reported, titled “Leather made from the hides of double-muscled
cattle has satisfactory physical characteristics”, in the Journal of the
American Leather Chemists Association 96:393-397, 2001. Piedmontese cattle
with 2-copies of non-functional myostatin actually produced leather with higher
tensile strength !
Another
research project on leather quality, conducted in Poland on various breeds and
breed crosses, supports these findings. “Hides obtained from two-breed crosses by Angus
bulls, as well as from three-breed crosses by Piedmontese and Angus bulls,
showed the most uniform structure. The skin tissue obtained from crosses by
Piedmontese and Angus bulls was characterized by a large number of collagen
fibres in a bundle, small thickness of bundles and small distance between them,
what has a considerable positive effect on the properties of leather.” Animal Science Papers and Reports vol. 20 (2002) Supplement 1,
243-249 Institute of Genetics and Animal Breeding, Jastrzêbiec, Poland.
Today,
there are collagen diets, and collagen sausage casings, facial injections and
collagen creams. We want more of it in our leather and less in our meat.
In
summary, collagen has a dramatic influence on all of our lives. As the most
abundant protein in our bodies, and in our cattle’s bodies, it is comforting to
know that science is researching its amazing properties.
Vicki
Johnson
Executive
Director
North
American Piedmontese Association (NAPA)
PO Box 330
Valleyford,
WA
99036-0330