|MadSci Network: General Biology|
Interestingly plants, animals and indeed all forms of life have color. Yes, these colors are predetermined genetically, whether they are red cabbage, green lobsters or the green leaves we see change color in the fall. Your purple beans are purple due to a pigment known as anthocyanins, responsible for that purple, reddish range of colors. When cooking, a chemical change did take place. What happened was the heat from the cooking broke apart the molecules on the surface of the bean and exposed the chlorophyll which is green. In my other examples cooking destroys the lobsters' greenish 'coat' and uncovers its carotene underlayer, thus orange lobsters. Nature plays similar tricks with leaves. As the weather changes due to cooler nights and shorter days, the sugars stop providing nutrients to their leaves and the different pigments that lay under the green show up. Such pigments as the anthocyanins that you noted in your purple beans. Hope that helps. Books that explain such chemical processes are: The Cookbook Decoder by Arthur Grosser; On Food and Cooking by Harold McGee.
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