Through the process of cooking, molecular transformations alter the macroscopic properties of our food. Consider what happens when you fry an egg: the transparent, liquid egg whites become an opaque white solid. These striking changes in the egg’s color and texture are a result of protein denaturation. A raw egg white is essentially a suspension of proteins in water. These proteins are made of long chains of amino acids that “fold” into specific and stable three-dimensional structures. Heating the proteins in an egg white causes them to “unfold” and no longer maintain their inherent structure. In this state, proteins are said to be denatured and will readily stick to one another to form an extensive protein network.
The formation of such denatured protein networks underlies many of the macroscopic changes we observe during the cooking of protein-rich foods such as eggs and meat. The extent of protein network formation affects the final texture of cooked meat and eggs. A steak cooked medium-well, for example, will have a denser protein network that gives rise to a tougher steak than one that is cooked medium-rare [1]. Denatured protein networks also affect the optical properties of protein-rich foods. Because a cooked protein network scatters light more effectively than a suspension of uncooked proteins, eggs and fish become more opaque as they are cooked [2]. We usually associate cooking with heat-related processes, but there are other ways to denature proteins. For example, you can “cook” an egg in acetic acid: http://www.youtube.com/watch?v=KJSwlVOt12w This form of chemical cooking relies on high salt concentrations or extreme pH conditions to denature proteins and “cook” food. Although an egg “cooked” in pure acetic acid may not have broad taste appeal, chemical cooking is used to prepare a variety of edible dishes including brined salmon (lox), pickled herring, and lutefisk. In this recipe for ceviche, we will use an acidic (low pH) marinade to “cook” fish without heat.