About Collagen Breakdown In Meat
http://www.sweetbabymedia.com/recipes/allbynumber3/013001.shtml
John Isenhouer asked for a thesis on collagen. It won't take a thesis to discuss the process as it relates to BBQ. Meats are made of muscle, connective tissue, fat and bone. Muscle contains proteins and glycogen. As the temperature of the meat increases, glycogen, a long chain sugar, is reduced to simple sugars. This caramelizes and is responsible for one of the flavor components. Proteins (flavorless) are denatured to amino acids which not only have flavors themselves, but undergo Maillard browning reactions which adds another flavor component. While bone adds no flavor itself, the marrow is rich in methyglobulin and other proteins. This reacts with smoke nitrites to give us the smoke ring. You may have heard that "the sweetest meat is next to the bone". The proteins are reduced to amino acids. Nutrasweet is an amino acid. Fat is very simple cells which breakdown to sugars, fatty acids, and triglycerides at low temperatures. Collagen is proteins that have lots of side chain bonds. This makes them elastic. It takes more energy to denature them than the simpler proteins of muscle tissue. Energy in the form of heat will denature these proteins into the flavorful amino acids. If the temperature is too high, the water in the muscle cells and the fat is rendered out before the collagen melts. This results in dry, tough meat. Too low and you risk bacterial activity. Tough cuts of meat like brisket and pork butts benefit from low temperature cooking as the collagen adds flavor to the meat. Less tough, more expensive cuts do not need this phase and can be cooked at high temperatures for shorter periods. That is why ribs take only a few hours and briskets take 20.
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Fat can only be rendered in a dry cooking environment over a long period of time and at low temperatures. Here is what happens . . . the meat must attain a temperature of 160� - 170� to start the fat rendering process. At these temps, the meat temperature will 'plateau' . . . that is, it will stay at these temps for up to 2 hours on ribs and 4 and 5 hours on butts and briskets. What is happening is, the collagen (connective tissue) starts to break down . . . this process releases water, which in turn causes a cooling of the meat. So the temps stay steady. This collagen breakdown is what makes meat so tender.
Once this collagen completely breaks down, the temps will start to rise. It is this process that allows all of the fat to be rendered from a rib.
http://www.madsci.org/posts/archives/jan2001/980785018.Cb.r.html
I will answer your question based on my knowledge of Food Science and information provided in the text "Foundations of Food Preparation" 1996. 6th edition, J. Freeland-Graves & G. Peckham, Prentice Hall, Englewood Cliffs, NJ.
As the temperature increases during cooking, enzymes in the interior of the meat that degrade muscle proteins are activated. Between 104-122 F, protein chains begin to unfold and denature (proteins lose their quaternary and tertiary structure. These changes eventually cause the structure of the myofibrils to break and shorten. As the protein molecules aggregate, immobilized water is freed, decreasing the ability of the meat to hold water. You referred to this change in your question.
Protien denaturation and water loss from the muscle contribute to increase in toughness of meat during cooking. High temperatures results in the fat melting, and this fat can be absorbed by the meat or lost as drippings. The fat that covers the surface of the meat reduces water loss, which can aid in maintaining juiciness. Heat can also tenderize meat by breaking down connective tissue (collagen). The heat can denature the collagen resulting in the hydrolysis of the protein chains. The end product of this process is the formation of gelatin. Cooking at low temperatures for long periods of time causes two changes (1) Hydrolysis of collagen and (2) Breakdown of muscle fibers by proteolytic enzymes.
These two processes result in meat that is more tender. This is why it is recommended that one use slow cooking methods for tougher cuts of meat (i.e. pot roast). The color change that occurs to meat on cooking is a results of myoglobin breakdown (pigment that causes fresh hamburger to be red - oxymyoglobin). The surface of cooked meat browns as a result of the partial breakdown of its proteins, fat, pigments and other constituents. The browning that occurs on the surface of fried meat is the result of the Maillard reaction (reaction between the carbonyl group of a reducing sugar and and amino acid or amino group (i.e. that found on lysine)of a protein or peptide.
I hope this answers you question. Sincerely, Al Bushway, Professor of Food Science
http://forums.egullet.com/index.php?showtopic=40548#ref
If the object is to raise the internal temperature of the meat to 60C/140F, then why put it in a 200C/400F oven, overcook the outside, undercook the inside and hope they even out during the resting period? They won�t. The heat changes are irreversible. All that happens is the inside cooks a bit more from the retained heat and some of the juices squeezed out from the middle migrate a bit to the outside.
A much better idea is to put the meat in a much lower oven, say 65C/150F, for a long enough time for the entire joint to come up to temperature � about 5 hours. This also has the beneficial effect of letting the collagen denature to gelatin, as we shall see later. The meat will be uniformly tender, juicy and delicious. People will marvel. There is no danger of overcooking, so timing is not critical.
Stewing, boiling, or braising uses wet heat, and another mechanism comes into play. The glue that holds the muscle together dissolves slowly. This glue is made up of different proteins, primarily collagen. Collagen consists of three strands of molecules wound around each other. The older the animal, the greater the amount of collagen. Likewise, the more active the muscle, the greater the amount of collagen.
With long, slow cooking, those strands will unwind and turn to soft, succulent gelatin, providing the juiciness to tough cuts of stewing beef like oxtail and shin This however is a comparatively slow process. If you cook it long enough for all of the collagen to turn to gelatin, and hot enough for the contraction of the meat to squeeze out the liquid, you have just the cooked meat fibers. If they have been overcooked, you are left with irretrievably dry and stringy meat. Even if it is swimming in liquid, you can�t get that juiciness back into the fibers that the curled up proteins have squeezed out.
Collagen starts to turn into gelatin and dissolve at around 60C/140F. This process (and also the fat melting) takes energy. Experienced BBQ cooks know that during the long slow smoking of brisket there is a "temperature stall" at around 72C/165F, where the internal temperature, instead of continuing to climb, stays steady for a long time before increasing again. That is the period the collagen is converting to gelatin. Once the temperature starts to climb again the conversion is complete, and the meat is tender. Any more cooking tends to dry the meat without improving tenderness.
Heston Blumenthal says that softening the collagen also improves even normally tender cuts of meat, such as the roast beef above. He suggests holding the temperature of the beef for up to 10 hours at 55C/130F (longer will start to generate �off� flavors) to make beef that is "unbelievably tender."
Wet cooking is appropriate for the tougher (but flavorful) pieces of meat that have a lot of connective tissue. The long, slow moist cooking melts the toughness into smooth unctuousness. The tougher pieces of meat can stand the long cooking and will become tender as the collagen dissolves. Even so, although they are fairly tolerant, overheat them and they too will fall apart into dry, tough shreds. These joints have much more flavour than the softer joints
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