By Harold McGee
Carotenoids are so named because the first member of this large family to be chemically isolated came from carrots. These pigments absorb blue and green wavelengths and are responsible for most of the yellow and orange colors in fruits and vegetables (beta-carotene, xanthophylls, zeaxanthin), as well as the red of tomatoes, watermelons, and chillis (lycopene, capsanthin, and capsorubin; most red colors in plants are caused by anthocyanins). Carotenoids are zigzag chains of around 40 carbon atoms and thus resemble fat molecules. They’re generally soluble in fats and oils and are relatively stable, so they tend to stay bright and stay put when a food is cooked in water. Carotenoids are found in two different places in plant cells. One is in special pigment bodies, or chromoplasts, which signal animals that a flower is open for business or a fruit is ripe. Their other home is the photosynthetic membranes of chloroplasts, where there is one carotenoid molecule for every five or so chlorophylls. Their main role there is to protect chlorophyll and other parts of the photosynthetic system. They absorb potentially damaging wavelengths in the light spectrum, and act as antioxidants by soaking up the many high-energy chemical by-products generated in photosynthesis. They can do the same in the human body, particularly in the eye. Chloroplast carotenoids are usually invisible, their presence masked by green chlorophyll, but it’s a good rule of thumb that the darker green the vegetable, the more chloroplasts and chlorophyll it contains, and the more carotenoids as well.