Carotenoid

Carotenoids are yellow, orange, and red pigments that come from plants, algae, some bacteria, and fungi. They give color to many foods and animals we see every day, like pumpkins, carrots, corn, tomatoes, canaries, flamingos, salmon, lobster, shrimp, and daffodils. Scientists have found over 1,100 different kinds of carotenoids, which can be grouped into two types: xanthophylls, which contain oxygen, and carotenes, which are made only of hydrocarbons and have no oxygen.

All carotenoids are made from eight isoprene units and have 40 carbon atoms. They absorb light in the violet to green range, which is why they look yellow, orange, or red. In plants and algae, carotenoids help with two important jobs: they catch light energy for photosynthesis and protect the plant from too much sunlight. Some carotenoids, like β-carotene, α-carotene, β-cryptoxanthin, and γ-carotene, can be turned into vitamin A in our bodies. In our eyes, pigments like lutein, meso-zeaxanthin, and zeaxanthin help with vision, and scientists are still studying exactly how they work.

Structure and function

Main articles: carotenes and xanthophylls

Carotenoids are special pigments made by plants, algae, and some tiny living things. They give color to many foods like carrots, tomatoes, and corn, and they also help plants turn sunlight into energy. These pigments have many connected parts that let them soak up different colors of light.

Carotenoids come in two main types: carotenes, which have only carbon and hydrogen, and xanthophylls, which also have oxygen. They help plants in many ways, like protecting cells from damage and helping control how plants grow. Their bright colors — from yellow to red — come from their special structures.

Regulation

The production of carotenoids in plants is influenced by different factors. Genes that control carotenoid production can be activated by light, which helps plants make more carotenoids. Plant hormones, such as auxins and abscisic acid, also play a role by affecting how much carotenoid a plant produces, especially when the plant is under stress.

Environmental conditions, like drought or attacks from pathogens, can also cause plants to produce more carotenoids. This extra production helps the plant protect itself and stay strong in tough conditions.

Morphology

Carotenoids are found outside the cell nucleus in places like lipid droplets and granules inside cells. Scientists have used special tools to see and measure these pigments in cells, especially in tiny plants called algae. By creating special proteins, researchers have also been able to find a specific type of carotenoid called lycopene in both animal and human cells.

Foods

Beta-carotene, found in pumpkins, sweet potato, carrots, and winter squash, gives these foods their orange-yellow colors. Dried carrots have the most beta-carotene of any food. The Vietnamese gac fruit has lots of lycopene, a type of carotenoid that gives tomatoes their red color. Even green foods like kale, spinach, collard greens, and turnip greens contain beta-carotene.

Carotenoids are important for our health. They help us see better, support our immune system, keep our skin healthy, and may even help prevent some diseases. Animals, including flamingos, get their colorful feathers from carotenoids in their food. Humans need to get carotenoids from the foods we eat because our bodies cannot make them. Eating these foods with some fat, like oil, helps our bodies absorb the carotenoids better.

Plant colors

Carotenoids are pigments that give yellow, orange, and red colors to many plants. They are found in fruits like tomatoes and vegetables like carrots, as well as in leaves during autumn when the green chlorophyll fades away.

These pigments also color the leaves of many trees in the fall, such as hickories, ash, maple, and birch. While carotenoids create yellow and orange colors, red and purple hues in autumn leaves usually come from a different kind of pigment called anthocyanins.

Bird colors and sexual selection

Dietary carotenoids and their metabolic derivatives are responsible for bright yellow to red coloration in birds. Studies estimate that around 2,956 modern bird species display carotenoid coloration, and the ability to use these pigments for external coloration has evolved independently many times throughout avian history. Carotenoid coloration shows high levels of sexual dimorphism, with adult male birds generally displaying more vibrant colors than females of the same species.

These differences arise due to the selection of yellow and red coloration in males by female preference. In many bird species, females invest more time and resources into raising offspring than males, so they carefully choose high-quality mates. Bright carotenoid coloration is often seen as a sign of male quality, possibly because it affects immune function or cellular respiration. However, in some cases, such as with stickleback fish, more colorful males might not be the best choice, as they may not protect their sperm as well from damage.

Aroma chemicals

When carotenoids break down, they create special chemicals like ionones, damascones, and damascenones. These chemicals are used to make lovely smells in perfumes. Even though they are found in small amounts, β-damascenone and β-ionone give flowers, like the rose, their sweet scent. These same nice smells can also be found in black tea, aged tobacco, grape, and many fruits.

Disease

Some bacteria make carotenoids to protect themselves from harm. For example, a carotenoid called staphyloxanthin gives some strains of Staphylococcus aureus their golden color. This pigment acts like a shield, helping the bacteria avoid damage from substances the immune system uses to fight infections.

Biosynthesis

Carotenoids are built from small molecules called isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Plants use two pathways to make these building blocks. One pathway, found in the parts of the cell that aren’t chloroplasts, is used to make cholesterol in animals. The other pathway, used in chloroplasts, helps create carotenoids.

The process starts with two molecules of geranylgeranyl diphosphate (GGPP) joining together. This forms a colorless molecule called phytoene, which then changes into lycopene, a red molecule. Lycopene can change into different carotenoids like α-carotene and β-carotene. These can be further changed into xanthophylls, which add colors like yellow and orange to plants.

Naturally occurring carotenoids

Carotenoids are colorful pigments found in many plants and other organisms. They give bright yellow, orange, and red colors to foods like pumpkins, carrots, tomatoes, and corn, and also color animals such as flamingos and salmon.

Over 1,100 different carotenoids have been identified. They can be grouped into two main types: xanthophylls, which contain oxygen, and carotenes, which are made only of carbon and hydrogen without oxygen. These pigments play important roles in nature, such as protecting living things from harmful sunlight and helping some organisms make food.