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6.3: The Role of Proteins in Foods- Cooking and Denaturation

  • Page ID
    40606
    • Contributed by Jennifer Draper, Marie Kainoa Fialkowski Revilla, & Alan Titchenal
    • Faculty (Food Science and Human Nutrition Program and Human Nutrition Program) at University of Hawai‘i at Mānoa

    In addition to having many vital functions within the body, proteins perform different roles in our foods by adding certain functional qualities to them. Protein provides food with structure and texture and enables water retention. For example, proteins foam when agitated. (Picture whisking egg whites to make angel food cake. The foam bubbles are what give the angel food cake its airy texture.) Yogurt is another good example of proteins providing texture. Milk proteins called caseins coagulate, increasing yogurt’s thickness. Cooked proteins add some color and flavor to foods as the amino group binds with carbohydrates and produces a brown pigment and aroma. Eggs are between 10 and 15 percent protein by weight. Most cake recipes use eggs because the egg proteins help bind all the other ingredients together into a uniform cake batter. The proteins aggregate into a network during mixing and baking that gives cake structure.

    Colorful birthday cake on a cake stand with a slice of cut out Figure \(\PageIndex{1}\): Image by Annie Spratt on unspash.com / CC0
     

    Protein Denaturation: Unraveling the Fold

    When a cake is baked, the proteins are denatured. Denaturation refers to the physical changes that take place in a protein exposed to abnormal conditions in the environment. Heat, acid, high salt concentrations, alcohol, and mechanical agitation can cause proteins to denature. When a protein denatures, its complicated folded structure unravels, and it becomes just a long strand of amino acids again. Weak chemical forces that hold tertiary and secondary protein structures together are broken when a protein is exposed to unnatural conditions. Because proteins’ function is dependent on their shape, denatured proteins are no longer functional. During cooking the applied heat causes proteins to vibrate. This destroys the weak bonds holding proteins in their complex shape (though this does not happen to the stronger peptide bonds). The unraveled protein strands then stick together, forming an aggregate (or network).

    Illustration of a normal protein which goes though denaturation (the lose of biological activity with the agents of pH, temp, ionic strength, and solubility) and leads to a denatured protein Figure \(\PageIndex{2}\): Protein Denaturation. When a protein is exposed to a different environment, such as increased temperature, it unfolds into a single strand of amino acids.

     

    Query \(\PageIndex{1}\)