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Heat from cooking changes the shape of protein in foods and, in some cases, triggers reactions between amino acids and other substances. Most of these changes are good because they make foods more digestible and develop flavor. But when red meat is exposed to very high temperatures, amino acids produce substances that may increase the risk of cancer.
Change in Structure
The first step in protein production occurs when amino acids connect together to form a long chain. In the next step, the chain coils or folds to form a secondary structure. In the final step, it folds again to create a three-dimensional form known as the tertiary structure.
In a process called denaturation, heat breaks the bonds that hold together the secondary and tertiary structures, but it doesn't alter the original chain of amino acids. Some proteins denature at 110 degrees Fahrenheit, but most unfold around 130 degrees Fahrenheit, reports Bellevue College.
Since the chain of amino acids stays the same even after proteins are heated, the amino acids are still available for your body to absorb and use. In fact, proteins must be denatured before they're digested. Eliminating the secondary and tertiary structures is the only way for digestive enzymes to reach the primary chain of amino acids.
Boost of Flavor
When they're heated, proteins on the surface of food combine with sugars, which causes browning and develops flavors. This process, called the Maillard reaction, begins when foods are heated above 285 degrees Fahrenheit, according to the Science of Cooking website.
While the Maillard reaction improves flavor, you'll also lose some nutrients. The amino acids that combine with sugar change form, so they're no longer available as amino acids.
Effect on Milk Proteins
Milk contains two groups of proteins -- casein and whey -- which react with one another at high heat. This is beneficial for some purposes, such as making cheese, because it prevents curds from forming.
Casein and whey have different physical characteristics that make whey proteins more sensitive to heat. Whey withstands pasteurization but denatures at higher temperatures. Denatured whey can bind with more water, which improves the consistency of products such as yogurt, reports Milk Facts.
Dangers of High Heat
At high temperatures, amino acids react with creatine, which is naturally found in muscles, to form heterocyclic amines. HCAs are a concern because they may increase your risk of cancer.
Beef, pork, fish and poultry can all form HCAs, but the biggest danger comes from red meat, according to a study in Nutrition and Cancer in October 2013. HCAs are more likely to develop when meat is in direct contact with a metal pan and cooked at 300 degrees Fahrenheit or higher.
Acrylamide is formed when a specific amino acid -- asparagine -- reacts with sugars, which happens at high temperatures reached during frying, roasting and baking. You don't have to worry about acrylamides developing in meat, fish or dairy. They only form in plant foods, especially carbohydrate-rich potatoes that are fried. Acrylamide increases the risk of cancer in lab animals, but its effect in people is still being studied.