Denaturation & CoagulationDenaturation and coagulation are often referred to as the Siamese twins of food science because they almost always occur together. Both of these chemical reactions involve proteins. Denaturation is the permanent alteration of protein structures by heat, acid or agitation. It breaks the chemical bonds (hydrogen and disulphide bonds) that hold amino acids together and unravels the helical structure. Coagulation is the "setting" of protein when heat or acid is added. It traps liquids inside a solid.
The pictures to the right are examples of foods that undergo denaturation and coagulation in their production process. |
In this recipe... |
In the recipe for beef stir-fry, beef is involved in denaturation and coagulation. Beef is the source of protein in this recipe. It is the protein that is being denatured and coagulated. The mixture of onion, garlic, barbecue sauce, oyster sauce are involved in the denaturing of beef. Marinating the beef is part of the denaturing process. There is also a small amount of protein in the vegetables (bok choy, carrot, celery) that denature and coagulate, albeit not that much.
Analysis of chemical reaction in method: The lean beef and vegetables are cut up in step 1, beginning the denaturing process. By slicing, the chemical bonds in the protein break and the helical structure of the amino acids unravels. This denaturing process for the beef continues in step 2 when it is marinated and mixed with other ingredients. In step 4, the proteins in the vegetables coagulate and make them softer, easier to chew and easier to digest. This continues in step 6 and 7. In steps 5, 6 and 7, the protein in the beef undergoes coagulation as it is being cooked. It is also being denatured as the mixture is stirred. By applying heat, the protein "sets" and the meat juice is caught in the muscle. This is because the proteins form a network that traps liquids and creates a colloidal suspension. |
Physical changes |
There are many physical changes that occur during denaturation and coagulation. The listed physical changes are specifically related to the meat because it has more significant changes to it than the vegetables which only have very little protein in them to denature and coagulate, but the main physical changes to the vegetables are: they get softer and easier to digest.
The meat changes from red to brown when it goes through coagulation, but this change is not as noticeable in this recipe because the beef would be covered in a mixture of sauces. After coagulation, the aroma of the meat would be mixed with other ingredients such as garlic and onion. It would smell cooked instead of raw. The meat in this recipe would have been mixed with garlic, onion, oyster sauce and barbecue sauce, as a part of denaturation. The taste of these ingredients would be added to the taste of cooked beef. The changes in the appearance of the beef during denaturation and coagulation would mostly relate to the changes in colour. Also, the shape of the beef changes when it is sliced. Depending on how long the beef is cooked for, it can either end up having a chewy texture or a dry texture, instead of the slimy texture of raw meat. The safety of consuming the meat also changes after coagulation. There is lots of bacteria in raw meat, but cooking it kills off the bacteria and the meat would be much safer to consume. |
Evaluation of recipe
The two chemical reactions denaturation and coagulation are an integral part of making beef stir-fry. Without them, you would be eating raw beef and vegetables that are hard to digest. Denaturation and coagulation greatly improve the food safety and eating quality of the beef stir-fry.
The physical changes of the recipe that are brought about by denaturation and coagulation are listed above. These, while also improving the taste, texture and aroma also improve the safety of consuming the beef. There are large amounts of bacteria in raw beef that are harmful when digested and coagulating the beef at high temperatures kills them off so the food safety is improved significantly.
Two significant factors that can determine the success or failure of the recipe are the amount of time the beef is cooked for and the temperature it is cooked at. While this recipe does not specify the amount of time needed to cook the meat for, it is important to ensure that the beef is cooked for a sufficient amount of time so that the centre is not still raw when it is served. It is also important not to over-coagulate the beef or the surface will have a black bitter layer of burnt meat that is unpalatable as it is unhealthy. The temperature to cook the meat at is not specified, but this is also something that is important to get right. If the temperature is too low, the meat will take too long to cook or it will still be raw when served. Cooking it at temperatures that are too high also may burn it. To make sure that the beef is cooked, the time and temperature needs to be balanced. High cooking temperatures equals fast cooking time and low temperature equals longer cooking time. The colour of the beef is usually a good indicator of whether it is cooked.
The physical changes of the recipe that are brought about by denaturation and coagulation are listed above. These, while also improving the taste, texture and aroma also improve the safety of consuming the beef. There are large amounts of bacteria in raw beef that are harmful when digested and coagulating the beef at high temperatures kills them off so the food safety is improved significantly.
Two significant factors that can determine the success or failure of the recipe are the amount of time the beef is cooked for and the temperature it is cooked at. While this recipe does not specify the amount of time needed to cook the meat for, it is important to ensure that the beef is cooked for a sufficient amount of time so that the centre is not still raw when it is served. It is also important not to over-coagulate the beef or the surface will have a black bitter layer of burnt meat that is unpalatable as it is unhealthy. The temperature to cook the meat at is not specified, but this is also something that is important to get right. If the temperature is too low, the meat will take too long to cook or it will still be raw when served. Cooking it at temperatures that are too high also may burn it. To make sure that the beef is cooked, the time and temperature needs to be balanced. High cooking temperatures equals fast cooking time and low temperature equals longer cooking time. The colour of the beef is usually a good indicator of whether it is cooked.