Hard boiled eggs and well-done meat: What’s a protein to do?
By Sara Gannon, Behavioral Neuroscience, 2021
Most people are familiar with the concept of proteins, an essential nutrient that is found in foods like eggs and meat. But what are proteins and why do foods that are high in them change so drastically when cooked?
Proteins are complex molecules composed of a long chain of amino acids, which serve as building blocks. Each protein is distinct not only in the order of amino acids, but the unique formation created when you have hundreds, or thousands, of amino acids bonded together. The molecular interactions between these amino acids creates coiling and folding, giving proteins their unique structures. This structure is what allows a protein to have a specific function. For example, the shape of an enzyme’s active site must match the shape of its target substance, or substrate, in order to properly recognize the correct substance.
When a protein is exposed to a sufficient increase in temperature, it will unfold into just a single strand of amino acids.
It follows that the change in the structure of a protein would lead to the loss of that protein’s specific function. This process is called denaturation, and can be caused by external stress on the protein, such as a large shift in environmental acidity, salinity, radiation, or heat. For example, when a protein is exposed to a sufficient increase in temperature, it will unfold into just a single strand of amino acids. While heat causes the arrangement or structure of the protein to change, it allows the order of the amino acids to remain the same.
So why is this important? It’s believed that the denaturation of proteins is a mechanism that determines many biological laws that we take for granted. For example, it explains why a high fever is so dangerous. The explanation is in the proteins; temperatures above 105.8°F are sufficient to break molecular interactions between amino acids and denature proteins, leading to significant changes in protein shape and function, potentially rendering them unfunctional. A fever of 106°F has the potential to be deadly, considering proteins make up not only your skin and muscles, but also the digestive enzymes in your stomach and the antibodies that protect your body from viruses and disease.
Aside from the dangers, there are also interesting and useful interactions that can occur during protein denaturation. For example, think about how fresh pineapple tastes — it has a bit of bite, and sometimes you even experience a slight burning sensation on your tongue or in your mouth. This is because the fruit contains a protein called bromelain, which functions to break down other proteins. So when you’re eating pineapple, it actually tries to eat you back! Now think about how pineapple tastes once it’s been cooked — sweet and devoid of any burning sensation. This is because through the process of cooking, heat has denatured the proteins in the pineapple. The bromelain has been broken down and its function rendered useless.
The fruit contains a protein called bromelain, which functions to break down other proteins. So when you’re eating pineapple, it actually tries to eat you back!
Moreover, proteins and their denatured qualities can serve some very important roles in modern-day cooking. For one, they are an excellent binding substance. The reason that eggs are used in most baking recipes, such as cake or cookies, is because as the proteins denature, the unraveled strands bind and stick together to form a matrix-like network throughout the substance. This network of denatured proteins provides structure and uniformity throughout the baked good.
Another great example of the use of denatured proteins is when fish is cooked using acidity (and no heat)! The acidity alone functions as an environmental stressor strong enough to unravel the protein structures and sufficiently “cook” the fish. The proteins become denatured just as they do with exposure to heat.
Taken these examples, it’s quite evident that proteins, in their denatured form and otherwise, serve an important role not only in the lives of humans, but in all of biological life. And scientists agree — there are many groups studying and pushing the boundaries of natural protein law. When you think of a hard boiled egg or cooked meat, it seems quite obvious that a molecular change like that is irreversible. However, scientists have recently discovered evidence that it’s not. In 2015, researchers at the University of California Irvine discovered a way to un-boil an egg. One characteristic of denatured proteins is the tangling of long chain of amino acids, and this scientific group successfully reversed the protein tangling by using a vortex fluid device. A discovery such as this one might not mean much to cooks, but could serve to reinvent scientific strategies in the field of molecular biology.
Journal of Food Processing and Preservation (1994). DOI: 10.1111/j.1745–4549.1994.tb00240.x
Biochemistry (1994). DOI: 10.1021/bi00207a018
