Carotenoid Pigments: Definition & Structure

Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

From autumn foliage to summer fruits, vegetables, and flowers, discover how carotenoids help colorfully paint our world. Explore how carotenoids are important for the health of both plants and humans alike.

Carotenoids in Our World

If you had the pleasure of taking a scenic drive through New England in the fall, you would experience a dramatically colored display of foliage. The leaf colors change red, orange, and yellow during the season. These brightly colored leaves are the result of carotenoids, among other pigments.

What are Carotenoids?

Photosynthesis is the process by which plants convert light energy to chemical energy, thus giving the cells the compounds they need to survive. Both algae and plant cells contain chloroplasts, where photosynthesis takes place. Chloroplasts contain pigments, such as carotenoids and chlorophyll, in order to absorb light from across the color spectrum. Different colored pigments are able to absorb different wavelengths of light, such as the green color of leaves found in the pigment, chlorophyll.

Carotenoids are also found in cyanobacteria, or blue-green algae. While plants always receive light energy from the green pigment chlorophyll, they can also benefit from the additional light absorbing ranges of the carotenoid pigments. However, a plant cannot survive with carotenoid pigment alone. It must have chlorophyll to perform its vital energy-producing functions.

Beautiful autumn colors can be seen only because chlorophyll breaks down, rendering the carotenoid pigments more visible. It's not just fall foliage for which we can thank carotenoids. The emergence of red, orange, and yellow flowers in the warmer months is partially due to carotenoids, as are brilliant fruit and vegetable colors.

Carotenoid Structure

Carotenoids are oil-soluble molecules. Most are comprised of 40 branched carbon units bonded together. Structurally, they're composed of conjugated double bonds, meaning the carbon units are bonded together by alternating single and double bonds. The amount of conjugated double bonds a carotenoid contains changes the wavelength of light that it can absorb. As a result, carotenoids vary in color from red, orange, and yellow.

Carotenoid Structure
Carotenoid Structure

Carotenoid Properties

Carotenoids can be broken down into multiple categories, including carotenes and xanophylls. Carotenes are typically orange and yellow pigments, while xanophylls are yellow pigments. If you guessed that the term 'carotenes' originated with the carrot, you're correct! Carotenes were first discovered in the early 19th century in carrot roots. Carrots contain beta-carotene, a type of carotene that converts to vitamin A in our bodies. Lycopene causes the bright red color in tomatoes, and is known for its healthy anti-oxidant properties.

Carotenoid Color Diversity in Carrots
Carotenoid Color Diversity in Carrots

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